New update on Embedded Foil Glass, Stevens & Williams, Matsue Nokay, Aventurine & Silveria.
Basic glass, Glass color & Glass Types
The first step to understanding
the different "Types of Glass" is to know how clear "Basic
Glass" is made. Next, we will discuss what chemicals are
used to manufacture or improve clear basic glass. Addition will
cover the metals required to produce the various colors of glass.
Finally, we discuss each individual "Types of Glass", its associated
chemical formulation and or what manufacturing process is required to
produce that individual type of glass.
Some people will tell you that glass can be defined as a super cooled liquid and there is some justification for that statement. Glass is generally classed an amorphous solid below its glass transition temperature from a physics standpoint. Let talk about how glass is made. In real world English, glass (a solid material though quite fragile) is made by melting solid material with great heat. It can only be worked with, in a molten state. It can have both transparent and opaque properties. Transparent means you can see through it like clear glass or opaque you can see through it like Milk Glass.
The basic ingredients for clear glass are:
Silica, (SIO2) the major component in sand and has a melting point 1600 - 1800C. Sand has a melting point of approximately 2000C or 3632F depending upon the trace metals contained in the sand. Historical glass had higher melting points than modern glass due to modern improvements in the refining process of the raw materials.
Sodium Carbonate, (Na2CO3) by adding this ingredient it lowers the melting point of the Silica mix to 1000C or 1832F. Unfortunately the soda in glass makes it water soluble. Sodium unless stabilized or replace will dissolve in water.
Calcium oxide, (CaO) also known as lime obtained from limestone, some Magnesium oxide, (MgO) and Aluminum oxide are added to make the glass more chemically durable.
Heat, lots and lots of heat are required. The originally heat source was wood, historically followed by coal and more recently Natural gas. These ingredients when heated, produced what is known as Soda-lime glass which is 70% to 72% Silica by weight. Soda-lime glass amounts for 90% of all glass produced today.
Most common Soda-lime glass has other ingredients added to change its properties. Examples of the additives are Lead, Lead crystal or flint glass to make the glass more brilliant. Boron is used to change the electrical or thermal properties of the glass. Barium and Thorium oxide makes glass have a higher refractive quality required in high quality lenses. In modern glass lanthanum oxide has replaced Barium and Thorium oxide due to their radioactive.
The next step we add metals by formula to our molten glass to make different colors.
Iron oxide if added produces bluish-green glass.
Chromium if added produces a richer green color.
Sulfur, carbon together with Iron salts produces amber glass ranging from yellowish to almost black. In glass made from silica (sand) containing high levels of boron, adding sulfur will make blue glass. In the same boron rich silica adding calcium will make yellow glass.
Manganese is added in small amounts to remove a green tint caused by small amounts of iron contained in silica sand. If it is used in higher concentrations it will produced Amethyst color.
Manganese dioxide, is also used to remove the green color from the glass. This material when used will slowly turn glass from clear to violet over many years.
Selenium is used to decolorize glass, or in higher concentrations to impart a reddish color. If it is used together with cadmium sulfide it produces a brilliant red colored glass know a "Selenium Ruby". DO NOT CONFUSE THIS WITH TRUE RUBY GLASS WHICH IS MADE WITH GOLD. Selenium red has an orange tint to it.
Cobalt is used to make blue glass. It produces the best blue color when it is used in glass containing potash.
Tin oxide with antimony and arsenic will produce an opaque white glass. This glass is commonly known as Milk Glass.
Copper oxide when used in a 2% to 3% level will produce turquoise color.
Copper in its pure metallic form produces a very dark red, opaque glass which is sometimes used as a substitute for gold in the modern production of Ruby colored glass.
Nickel will produce blue to violet and even black glass depending upon the concentration used.
Chromium when used makes dark green or even black glass, in higher concentrations. If it is used with tin oxide and arsenic it produces dark green glass.
Cadmium and sulfur will produce deep yellow colors used in glazes.
Titanium when added produces a yellowish-brown glass.
Metallic Gold when added will produce cranberry to ruby color depending upon concentrations.
Uranium when added to glass will produce a yellowish to green color. It is typically used form 0.1% to 2.0% today. Antique glass normally contains from 1.0% to 2.0% is know in the US as Vaseline glass, or Canary Yellow or in the past just as Yellow glass. In Europe it is known as Uranium glass. This type of glass will be fluorescent in the present of a black light. Uranium glass is not typically radioactive enough to be dangerous.
Silver typically in the form of silver nitrate when used will produce a range of colors from orange-red to yellow. The way the glass is heated and cooled will significantly affect the colors produced.
There are three types of Glass listed in this section: one, “Glass Formulation” (G.F.) which means it is based on modification to a basic glass formula, Two, it is based on a “Manufacturing Technique” (Mfg. Tech.) which means it is dependent upon manipulation during manufacturing process rather that a specific glass formula and three a “(Glass Formulation which requires special Manufacturing Technique” (G.F. & Mfg. Tech,) which is a combination of a required special formula and special unique manufacturing technique;
Immediately after the Glass type name we have noted which of the three categories the glass falls into.
Agate Glass, (Mfg. Tech.): A striped-pattern glass created by mixing molten glass of different colors. The colored bands resemble those of natural agate.
Akro Agate Glass started operations in Akron, Ohio in 1911 to produce marbles. In 1914 they moved their operation to Clarksburg, West Virginia where they produced glass until 1951. Akro produced marbles until 1933. In 1930 they began to make press glass mainly due to the increased competition in the marble market. Akro's pressed glass was opaque and most often there were colored streaks in the glass. They called this "blended colors" or "multi- colors" but today's collectors would recognize it by the name "slag glass".
Examples of Akro Agate Glass
Amberina - heat sensitive, (G.F. heat reactive & Mfg. Tech.): Amberina glass is always red on the top to shades of amber to yellow on the bottom. If a piece of he glass is yellow on top to shades of amber colored to red on the bottom is called Reversed Amberina.
The first Amberina made by New England Glass Company was produced by adding gold chloride to amber-colored glass while it was still molten. After the glass cooled, it was reheated, and the gold compound caused those parts of the glass that reached high temperatures to turn red.
Heat sensitive Amberina has been made by Fenton who added selenium and cadmium sulphide rather than gold chloride to the molten glass. They felt that since selenium- based red glass was easier to press into molds. I suspect that cost of raw materials may have been more of a motivating factor. It must be noted that Gold Chloride gives glass a pinkish red to true deep ruby red, selenium and cadmium sulphide imparts an orange cast to the red glass. Some collectors feel that selenium based Amberina is not true Amberina.
Mr. Joseph Lock and Mr. Edward D. Libby first patented Amberina glass in the USA in 1883 for the New England Glass Company. Mr. Lock was the designer for the Cambridge works and W. L. Libby and sons was the owner of New England Company. Mt. Washington Glass Company of New Bedford, USA also produced Amberina in the 1880s for a few years. There was dispute between the two companies which resulted in Mt. Washington calling their amberina glass "Rose Amber". In 1886 and injunction was granted against Mt. Washington and they stop producing Amberina glass or Rose Amber.
License from Libby/New England Glass were obtained by Hobbs, Brockunier and Company of Wheeling, WV, USA to produce Amberina glass. European companies including the French company Baccarat also produced Amberina. Some of the European companies were not making true "heat sensitive" Amberina. They were producing the pseudo Amberina which included Harrach.
Example of a Amberian Vase
Amberina - pseudo amberina, (Mfg. Tech.): One form of pseudo Amberina developed after 1920 it is simply amber colored glass with a thin flash coating of ruby glass over part of the amber glass piece. This type of pseudo amberina glass shows a sharp shift from amber color to that of the ruby. It does not show the gradual blending from yellow through amber to ruby which is the characteristic true heat sensitive amberina.
Harrach pseudo amberina, definition forthcoming.
Amethyst Glass, (G.F.): See Manganese under glass colors. Amethyst glass is any of the many glass wares made in the dark purple color of the gemstone called amethyst. Included in this category are many pieces made in the nineteenth and twentieth centuries. Very dark pieces are called black amethyst.
An example of a Amethyst Glass Rose Bowl which was enameled by Theodor Rossler of Bohemia, ca. 1918 - 1939
Aventurine Glass, (G.F. & Mfg. Tech.): Aventurine historically, is a glass in which metallic copper particles are suspended by being incorporated in a flame reduction process to give the glass a shimmer. Aventurine is also called Goldstone or sometimes Monkstone. Today Aventurine or Goldstone is made in a low-oxygen reducing atmosphere. The modern process consists of melting soda-lime glass containing copper salts in a reducing (oxygen depleted) environment, causing the copper salts to decompose to metallic copper. A green variation of the formulation is the result of chromium salts being decomposed to form green glass with sliver metallic crystals.
Aventurine is most often in the reddish-brown glass form containing atomic isolated precipitate crystals of metallic copper. The copper reflects light through the glass media making the fire or sparkle, i.e. the appearance of gold. Aventurine or Goldstone has also been produced in blue, violet, or more rarely green glass which has the appearance of having silver suspended in the glass.
Aventurine glass has also been called “Avventizio” roughly meaning adventitious and “Avventurato” meaning fortunate. It appears from the name that the first production of Aventurine glass was by accident or chance. History records the inventor to be Vincenzo Miotti, who was granted the exclusive right to make it by the Doge of Venice in 1677. The secret of its production was passed down through the family until they stopped making the glass in 1731. Other glassmakers tried to imitate it, especially the Bertolini brothers in the 18th century but their glass was inferior. In 1811, a Motti widow revealed the family secret to another glassmaker. By the mid 19th century several formulae for aventurine had been published with various improvements.
The collector will also find glass that contains pieces of Aventurine Glass within its body, without the total piece being made of Aventurine Glass. As an example of this, in 1888, the Old Roman design was introduced by Thomas Webb & Sons. The same year a complaint from James Couper & Sons of Glasgow alleged that T. Webb & Sons were deliberately copying and infringed their copyright of Clutha Glass. While the two glasses are similar, there are distinguishable differences. Clutha had speckles of Aventurine in the glass, while Webb’s did not.
Aventurine glass is one of the few man-made materials that supplied its name to a natural stone. The name Aventurine was later given to various forms of feldspar or quarts with mica inclusions.
Note: Embedded Foil Glass is not Aventurine Glass. They are totally two different glass manufacturing process. Remember, Aventurine will always appear to be nodular in structure due to how it is made. Glass which contains Aventurine, the Aventurine will always look nodular, gritty or sandy in structure and it will appear more 3 dimensional, unlike foil which looks flat.
It will be in bands or irregularly scatter throughout the glass or in only certain part of the glass body. If you encounter glass that has copper material that look flat and more or less regularly spread evenly through out the body of the glass, it is most likely embedded foil glass, NOT AVENTURINE. If it encased over a colored based with a clear top case there is a 99.9 % that is embedded foil NOT AVENTURINE.
Many knowledgeable auction houses, dealers and collectors, do not know the difference between Aventurine and embedded foil glass. They will mislabel glass frequently.
Below left is a modern Commercial available 9mm rod of Aventurine Glass. Right is close up embedded Foil in a burst foil technique.
Below is a rose bowl of unknown manufacture which contains Aventurine. I have magnified it significantly for reader's inspection.
(Future additional Aventurine / Foil Glass Photo Comparisons)
Blown-Out Glass, (Mfg. Tech.): and embossed pattern glass are interchangeable terms. Blown-out glass is a slang term, which is often used to describe glass that has been blown inside a mold which has a pattern machined into the surface of the mold. The molten glass takes the shape of the mold pattern and when properly cooled will maintain the mold pattern shape. In the case of Victorian glass most Blown-out glass is cased but not always.
Examples of different Blow-Out Rose Bowls
Brown Malachite Glass, (Mfg. Tech.): See Slag Glass.
Brown Marble Vitro - Porcelain, (Mfg. Tech.): See Slag Glass. The best way I know to describe this glass is it looks like a cross between Chocolate Glass and Slag Glass. Or maybe it looks like a chocolate marble.
Example of Brown Marble Vitro - Porcelain Glass. (Example of Rose Bowls unknown to writer)
Burmese, (G.F. heat reactive & Mfg. Tech.): Burmese is an opaque colored single layer glass shading from yellow on the bottom to pink on the top. Most often found in a satin finish due to an acid bath and rarely in the original shiny finish. The glass formula contains Uranium oxide with tincture of gold added. The Uranium oxide produced the soft yellow base color and adding gold produces the pink color part of the glass when the glass is re-heated in the furnace. The length of time in the furnace will determine the intensity of the pink color. If the piece of glass is again reheated it will return to the original yellow color.
Mr. Fredrick S. Shirley patented his Burmese glass formula in 1885 in agreement with the Mount Washington Glass Co. of New Bedford, MA. He found that adding certain minerals including calcium fluoride to a uranium oxide glass mix produced his Burmese. His formula was supposed to be not all that different from Joseph Lock’s amberina formula other than it had more uranium oxide.
Burmese glass was a favorite of Queen Victoria and in 1886 the British glass house of Thomas Webb & Sons received a license to produce not only the original form but their own version known as Queen’s Burmese Ware. Queen’s Burmese Ware was produced in tableware and decorative glass often with enameled decorations. (Link to a T. Webb Burmese Rose Bowl)
Example of Miniature Burmese Rose Bowl
Cameo Glass, (Mfg. Tech.): Dates back two thousand years to Rome. Cameo glass is a form of Case glass. On the multiple layers of glass, an image is cutout in relief, from the body of glass. The multi layers of glass form the contrasts for the image. The glass may be removed by manual hand cutting tools or by a cutting wheel.
The English were famous for their fabulous cameo glass pieces. The French produced cameo glass from 1850 until the Second World War. In French glass house such as Emile Galle, the Daums, and Muller Freres. In the USA small amounts of cameo was produced by others including Steuben and Tiffany. (Links to Cameo Glass Examples)
Carnival Glass, (Mfg. Tech. with Chemical treatment): Carnival glass is usually defined as pressed glass which has an iridized surface treatment. However, there was also glass blown into a mold which also received an iridized surface treatment but was not pressed. An example of this would be some of Northwood / Dugan glass line.
Hot glass, either out of the press or mold was exposed sprays, fumes, and vapors from heated metallic oxides. This treatment left a lustrous coating on the surface of the glass. It often produced a rainbow affect on the glass surface. Some times it is compared to oil sheen on the surface of water.
Carnival glass was not the original name for this type of glass it was called names like "Iridill" and "Rainbow Luster". Supposedly when the market for iridized glass slump in the 20s second quality iridized glass was given away as prizes at local carnivals, ergo the name Carnival Glass.
In 1908 the newly formed Fenton Art Glass Company was the first to make large scale volumes of Carnival glass. Carnival was also made by several US companies, including Northwood Glass Company in Wheeling, West Virginia, Imperial Glass in Ohio; Westmoreland from Pennsylvania; Dugan (later Diamond) in Indiana, Pennsylvania; and Millersburg, in Ohio. The bulk of US carnival production was between the years from 1908 to 1918. Dugan/Diamond Glass Company continued carnival production until 1931. In Europe carnival was produced through the 1920's and 1930's. In the 1950s due to interest form collector, Carnival began to be produced again.
Dugan Honeycomb left and Tri Fold right Rose Bowls are examples of Carnival Glass
Cased Glass, (Mfg. Tech.): Cased glass is sometime erroneously called Overlay Glass. Casing is a technique of putting successive layers of different colored glass over each other. Much of the time this is done to prepare the piece of glass for cutting to make Cameo Glass. However, in the case of Victorian Rose Bowls this is not the normal situation. The majority of Victorian Cased Glass Rose Bowls are not cut or engraved. A Rose Bowl when engraved normally has clear glass below Flash Glass (not Cased Glass) which on the surface. This process is sometime reversed and the Flash Glass is on the inside of the clear glass surface. Then they engrave through to the Flash Glass surface. The Flash Glass is thinner than the base clear glass so you most often find the engraving on the flash glass which is on the surface of the rose bowl.
Example of Case Glass Rose Bowl made by Stevens and Williams
Chocolate Glass, (G.F.): Chocolate glass was developed by Mr. Jacob Rosenthal. Mr. Rosenthal came to Greentown Indiana, to the Indiana Tumbler & Goblet Company in 1900. Greentown’s Chocolate glass was made from a formula known only to Jacob Rosenthal. The glass batch needed a source of carbon, and some of the men who worked with Rosenthal during 1900-1903 later revealed that oats or vine stalks were sometimes used to provide the chemical reducing agent so vital to this glass. In 1902, Rosenthal sold his formula for Chocolate glass to the National Glass Company the owners of Greentown plant. The Greentown factory was operated by a The National Glass Company a conglomerate of 19 plants which was formed in 1899.
Chocolate glass varies considerably in color and appearance, it ranges from light coffee with cream hue to a deep rich brown. Some items have a pronounced red-brown tone on the edges and are often called “red agate” by collectors today. Variegated streaks of color are sometimes present in the chocolate glass and collectors starting calling this “Caramel Slag” however there is no evidences any of this glass being called anything other the “chocolate glass” by the maker. Virtually all of the Greentown Chocolate Glass made was as pressed ware.
Chocolate Glass was made by the Indiana Tumbler and Goblet Company of Greentown, Indiana from 1900 until 1903. It was also made at other National Glass Company factories. At least two of the National plants - the Royal Glass Works in Marietta, Ohio, and the McKee & Brothers Works in Jeannette, Pa. - made Chocolate glass in 1902-03. Fenton Art Glass Company also made chocolate glass from 1907 to 1915. Imperial Glass Company also mad a similar type of glass which they called caramel slag.
Below is an example of Greentown Chocolate Glass. (We are unaware of Chocolate Glass Rose Bowls)
Cobalt Glass, (G.F.): See Glass colors Cobalt. Cobalt is a deep rich blue glass.
Example of two Cobalt Blue Rose Bowls a Modern Pilgrims on the left and A. H. Heisey Glass on right. Note, Older Cobalt typically has a deeper blue color probable due to the amount of cobalt used in the glass formulation. The older glass is usually thicker also.
Coralene Glass, (Mfg. Tech.): A Victorian form of decoration on glass. An image was painted onto a piece of glass with a thick syrupy enamel paint tiny glass balls were then applied to this surface. The piece of glass was then re-heated so the glass balls would partially melt into the surface of the glass piece. The finish surface looked like rough coral ergo the name.
Coralene was first patented in Germany in 1883 by Schierholz. It was soon after produced and exported from Bohemia. It was also made in the USA by MT. Washington Glass Company. Mt. Washington designs as well as those from Bohemia often imitated strands of coral in the patterns over the glass.
Crackle and Overshot Glass, (Mfg. Tech.): Crackle Glass is a process for making glass that supposedly was developed by Venetian glass makers of the 16th Century. This process requires molten hot glass to be immersed in cold water, which causes the piece of glass to crack. The glass is then reheated and either molded or hand blown into shape. The reheating of the glass seals the cracks in the glass. If you run your hand over the crackle glass outside you will feel the cracks but it will be smooth to the touch on the inside.
Some of the companies that have made Crackle glass include: Blenko Glass Company, Pilgrim Glass Company, Mt. Washington Glass Company, H.C. Fry Glass Company, Boston & Sandwich Glass Company, Hobbs, Bruckunier & Company, Cambridge Glass Company
Overshot Glass is a subset of Crackle glass. There are several ways to make Overshot Glass: one way was that the gather of hot glass, which was rolled over a steel plate (marver) that was covered with thousands of small pieces of glass. The bits of glass would adhere to the molten glass. The treated gather was returned to the furnace and reheated. This melted the small bits of glass causing them lose their sharpness. The gather was reheated and then blown into the desired object. Glass made this manner is usually smooth on the surface. A second way required the glass after being blown while still hot was rolled in glass fragments called “Frit”. After rolling in Frit the piece was usually returned to the furnace entrance soften the surface but not melt it. These surfaces are somewhat sharp to the touch.
Companies that produced Overshot Glass were: The Boston and Sandwich Glass Company, Hobbs, Brockunier & Company, Falcon Glass Works, as well as abroad, such as France, England and Bohemian factories.
Example of Overshot Glass Rose Bowl.
Custard Glass, (G.F.): Custard Glass is a slightly yellow opaque glass whose formula contains Uranium oxides. It will fluoresce under black light.
Custard Glass was first produced in England in about 1880. Northwood Company of Indiana, PA was the first company to produce a complete table setting from Custard glass prior to 1900. (See Vaseline Glass)
Example of Custard Glass Rose Bowl (Uranium Glass)
Cut Velvet Glass, (Mfg. Tech.): is a special type of art glass, that is a subset of MOP (see Mother of Pearl) also known as air trapped MOP. Cut Velvet Glass, as compared to the normal MOP, always has raised mold patterns on the exterior surface of the glass. It is always found with an acid finish or texture like velvet. The acid finish or technique is the same as Satin Glass (see Satin Glass); however the acid exposure may have been longer causing a bit smother surface.
This type of glass was made by many glasshouses during the Victorian period in the U.S., England and possibly Bohemia. Mt. Washington was one of the more notable U.S. producers of this type of glass.
Example of Cut Velvet Glass Rose Bowl.
Early American Pattern Glass (EAPG), (Mfg. Tech., set time span and specific types of glass): EAPG is a clear or colored pressed glass made from around 1850 until about 1914 in matched sets. It can also include some pattern glass that is blown into mold but not pressed.
Example of EAPG Glass.
This is from the 2012 annual GLDGC. Below is a great cross section of Early American Pattern Glass from several prominent Glasshouse assembled by Debi Raitz.
Embedded Foil Work, Glass: Burst Foil Glass (Mfg. Tech.) is often confused with Aventurine Glass (see Aventurine Glass for details) and Stevens and Williams Silveria and they are totally different techniques. Below you will find an excerpt from an email written by Mr. Stu Horn to the Rose Bowl Collectors Group explaining the Burst Foil Glass manufacturing technique:
“A GATHER OF MOLTEN COLORED GLASS (IN THIS CASE RUBY) IS COVERED WITH A THIN METALLIC FOIL AND THEN A LAYER OF CLEAR GLASS. THE PIECE IS EXPANDED ON THE BLOWPIPE - - THE THIN FOIL BURSTS INTO MANY PIECES IN A RANDOM SORT OF PATTERN.”
“FURTHER TO THIS - - APPARENTLY TO ASSURE A REASONABLY EVEN AND ATTRACTIVE BREAKAGE AND DISTRIBUTION OF THE FOIL- - - A SERIES OF RADIAL *RIBS* ARE APPARENTLY INCISED ON THE OUTSIDE OF THE MOLTEN GLASS BEFORE IT IS BLOWN. THESE INCISIONS ARE RATHER DISTINCT IN THE BOTTOM OF THE PIECE BUT BEGIN TO MEANDER AS THE *BRANCHING* OCCURS ON THE SIDES OF THE PIECE. LOOK CLOSELY AND YOU WILL SEE THE REMAINS OF THE RADIAL INCISIONS (LIKE CLEAR RIVERS) ON THE SIDES OF THE BOWL.” Stu Horn.
In most pieces of Burst Foil glass there are separation lines either of a regular or irregular pattern separating the different foil areas from each other on the piece of glass, see below.
The Burst Foil glass technique was produced by Edward Webb and Joseph Webb both producing their own versions in 1883, long before S&W produced Silveria in 1900.
Stevens and Williams' Silveria differed from Webb's foil work since their silver foil remained intact rather than breaking into fragments. Broken fragments of foil which are sandwiched between layers of glass constitutes the “Burst Foil Technique”, not Silveria which has intact foil.
There are many different types of embedded foil work, of which Burst Foil is the most common and there are famous examples of it by Edward Webb’s 1883, “Oroide and Agrentine”. He advertised the use of gold or silver foil between two layers of glass, respectively. Arthur John Nash was responsible for both designs.
Feathered Glass, (Mfg. Tech.): Feathering is done by applying threads of opaque glass to a layer of molten glass. The threads are rolled into the glass until level, and the hot surface is combed to produce a decorative feathery, wavy or zigzag effect. Feathered designs figured prominently in American Art Nouveau glass, and were a hallmark decorative feature of Quezal and Durand glass vases and lampshades. Feathering is also called "combing".
Flash Glass, (Mfg. Tech.): Flash glass is also called Plating. I am not sure why and I feel that it is an incorrect term usage, since plating refers to electro deposition of metals normally on metal. Flash glass is made through the process of applying a thing coating of molten glass normally over another glass object. Flash glass is about a thick as single sheet of paper and can be scratched. Occasionally flash glass can be applied within (inside) thicker glass object. Flashed glass can be and often is ground through to the thicker layer beneath to produce an effect somewhat similar to Cameo Glass. However, true Cameo Glass is Cased Glass not Flash Glass.
Flashing was used in medieval ruby windows. It consisted of a thin flashing of red glass over colorless base glass. We understand that some Sandwich and New England Glass pieces were made with this process. Much of the European cut-to-crystal uses flash glass process.
Flint Glass, (G.F.): Is a name for leaded glass produced in the USA and United Kingdom up to the 1860s. Flint glass name is applied to pressed pattern glass made from 1820s through the 1860s. In 1670 a better quality of glassware was perfected that contained powder flint in its formula, ergo the name Flint Glass. At a later date lead was added to the mix which produced even a greater clarity of glass. Powder flint was then dropped from the glass formula but the name stuck. Flint glass was fine glassware of its day. The term flint is sometime use synonymously with the term clear or white as descriptors of clear glass. When the "Flint" is use as a color term the glass may not contain lead.
Most Flint Glass formulas called for 33% lead which is about the same percentage as used in Waterford Crystal today. Most Modern crystal today contain between 24% to 28% lead. Pressed Flint glass pieces are typically having superior light refraction (brilliance) a resonance when struck (bell sound) and are heavy as compared to standard glass.
Example of modern Flint Glass Rose Bowl made by Waterford.
Frit Glass, (Mfg. Tech.): Frit Glass is a fine crushed glass that is applied to piece of glass either as and accent to original base glass or as an over all decorative coating. On Rose Bowls, Frit Glass accenting was used by Northwood Glass Company, Northwood/Dugan usually as a lip and crimp area accenting normally in conjunction with an Opalescent glass coating. The Dugan glass company used it as an over all decorations. Jefferson Glass Works was also known to use Frit Glass on the edges of some of their glass.
Frit glass application as an accent is as follows; molten glass after being blow into mold or free blown, next a limited application of Opalescent Glass would be applied certain areas, usually the soon to be crimp area, then the edges of the glass are rolled in “frit”. The frit then becomes embedded in the molten glass. The piece of glass is then returned to the “Glory Hole” to melt in the frit and active the Opalescent glass coating. Next we assume the glass rose bowl is crimped and annealed.
The second method is how Dugan made his Venetian glass rose bowls: it is similar to the first method except his entire rose bowl was rolled in the “Frit”. After the Frit was embedded in the molten glass, then the piece was hand shaped and “warmed in,” the frit oxidized, resulting in a silver-gold iridescence on the Dugan rose bowls.
A third method is also possible used on some rose bowls, is the glass was collected on the gathering rod then rolled in frit and then blown into shape.
Frit glass can also be ground into a fine powder then mixed with oil and chemicals to make enamel. The frit added to this combination aids in fusing color onto to a piece of glass.
Frit glass being worked into molten glass using a marver.
Photographic courtesy of Dave Fry.
Examples of Frit Glass Rose Bowls (National or Dugan)
Goofus Glass, (Mfg. Tech.): It is pressed glass which has been “cold painted”. The paint is applied but not fired like enameling. The paint is much less permanent than fired enamel. Goofus Glass is not usually encountered in rose bowls.
Most Goofus Glass was made from 1897 to 1911 though it was produced into the 1920s. It was produced in large volumes in the USA by Imperial Glass Company and Dugan Glass Company. Carnival glass forced it out of fashion from 1908 onward.
Examples of Goofus Glass
Hobnail Glass, (Mfg. Tech.): this type of glass is also sometime called "Dewdrop". Hobnail glass has a reoccurring pattern of raised knobs like the hobnail studs once used on boots. The hobnail pattern can be made by blowing glass into a mold or by pressing glass into a mold.
Hobnail glass was very popular during Victorian times, it was usually hand blown of translucent colored glass sometime called “Dew Drop Glass”.
Examples Hobnail Glass Rose Bowls
Stuart & Sons Rose Bowl, Photo courtesy of Stu Horn
Non attributed Rose Bowl, Photo Courtesy of Norma Nabers's Collection
Iridescent Glass, External Treatment, (G.F. and Mfg. Tech.) or (Mfg. Tech. with Chemical treatment): see Carnival Glass. There are two type of Iridescent glass the most common is when a chemical treatment is applied to hot glass as in the case of Carnival Glass. Please see Carnival Glass for detail description. This is a vapor or fume technique (see Photos Below). This type of finish is often referred to as having an Oil film on Water look.
The second form is when the Iridescent
Glass is created in batch or in-the-mix by means of formula and
manufacturing Technique. Examples of this type of glass is
Example of Iridescent Glass Rose Bowls (Dugan)
Example of Iridescent Glass Rose Bowls (In Batch).
This rose bowl was made by Pallme-Konig. We are refereeing to the gold sheen on the bottom in the 10:00 and 3:00 o'clock position. This appears to be in batch rather than fumed iridescent.
Latticino Glass, (Mfg. Tech.): Also know a Lace Glass, dates to 16th century Venice, where it was developed. The word Latticion is from the Italian for milk. The technique is also known as Filigrana (thread-grained). It can best be described as normally a white (sometimes it can be found in other colors) thread like pattern either spiraling within or producing a net like pattern with a secondary clear or colored transparent glass. Latticion Glass is often found used in high quality paper weights. It can also be found in modern Murrano Glass.
The finished glass object as in a paperweight may have the Latticino Glass as a base with the other Millefiori canes on top. Which appear like flowers atop lace. With other glass objects such as in a vase there may be only one Latticion Glass cane used or several with other types of glass separating them.
Marble Glass, (Mfg. Tech.): see Slag Glass.
Mary Gregory Glass, (Mfg. Tech.): Is a name applied to specific decorative style of glass enameling. The name Mary Gregory is of a decorator who work for the Boston and Sandwich Glass Company, she had absolutely nothing to do with this type of decorations.
Mary Gregory glass can be divided into early manufacture made between 1879 and 1939. Late production made after the Second World War to present day. Mary Gregory glass is a stylized fired, white enamel painting of a child usually outside, playing with such things as butterfly nets, bubbles, fishing rods, or hoops. The trees in the background often have a feathered style. The figures are oddly old-fashioned in it proportions.
This type of decoration developed from Painted Cameo glass which was a cheaper alternative to true cameo glass.
The predecessor to what is known as Mary Gregory glass was probably the “Quarkman” or “White People”. This was a decorative technique developed in Bohemia. According the Truitt’s book on Mary Gregory “Credit for originating high quality all-white enamel painting must be given to Friedrich Egermann (1777-1864) of Bohemia. As a young man, Egermann was fascinated by the quality of decorating being done on porcelain at Meissen. Posing as a deaf-mute, he secured employment there and was able to learn the process for mixing and firing enamel. Upon his return to Bohemia, he developed new methods of staining glass and elevated painting to the superior quality that became his trademark."
"Around 1815, Egermann began using small white dots, called "bisque pearls," to surround the cartouches and accent his decorations. The popularity of the pearls spread rapidly and soon other decorators incorporated them into their designs." *2
Early Mary Gregory glass is often found on Victorian colors of cranberry or bottle green. The quality of the painting is often of a high quality than modern versions. The highlights on key features and around the edges of the clothing may be double fired. The glass quality may be thinner or of a poor quality than modern blown glass. Rarely any other color than white is use on early pieces.
Example of Mary Gregory Glass, Pillow Vase
Example of Mary Gregory Satin Glass Rose Bowl, thought to by Muhlhaus. Circa 1920 - 1930
Mat-Su-No-Ke, (Mfg. Tech.): Is a decorating motif or style not a glass formula or manufacturing technique. However the proper identification of this decoration style is of importance to rose bowl collectors. Please follow the link listed, Mat-Su-No-Ke Details for more detail information. Also please see Stevens and Williams rose bowl section.
Milk Glass, (G.F.): Is an opaque white glass. True Milk Glass has the look of white porcelain. It was first made in Venice during the 14th or 15th century.
Milk glass with an opaque white appearance is usually made with tin oxide. Milk Glass with a semi-opaque white appearance is made with ashes of calcined bones. This kind of glass is sometime called; Opal glass, Opaline glass, and Milk-and-Water glass.
In the 20 century "Milk Glass" was formulated in blues (see below) and pinks yet still called Milk Glass even though it is a oxymoron. I never saw a cow give pink or blue milk!
Examples of Milk Glass
Left Fostoria Lincoln Drape, right Westmoreland and below, yes it is blue.
Millefiori Glass, (Mfg. Tech.): is an Italian word meaning thousand flowers. Millefiori Glass is manufactured by fusing many different colored and shaped glass rods called canes into one glass mass then shaping or manipulating this glass mass. You start by making each individual glass canes. The glassmaker starts by taking a gather of glass from the pot. The gather is then worked into shape on the marver. It can be clear or colored glass. Most often colored. The gather of glass can be rolled in powders then it is pressed into a mold of a different shape. This process can be repeated many times building several layers of color and design within the cane. At this point the rod may be three inches in diameter and six inches long.
The glass rod is reheated and a second pontil rod is attached to the other end of the glass rod. A second glassworker takes the second pontil working quickly the two of them, stretching and heating the glass rod until it is pencil thin and up to 30 feet long. The design within the rod is miniaturized accurately by this stretching process. Unfortunately only a small portion of the rod is even or consistent, so it can be cut into cross sections and used in the glass.
Many canes must be made of different color and pattern repeating the process above. After all of the canes have been made, they are arranged on a pattern metal template.
There are simple canes of a single pattern and there are complex canes which are made by bundling simple canes together then heating and stretching them again.
More complex patterns are made by again placing simple and complex canes on a pattern metal template. Finally in the case of a paperweight when all the canes are arranged in the desired pattern they are normally fused on the bottom with a single color darker glass and then encased around that and the top with clear glass.
The Millefiori canes below were manufactured by Whitefriars Glass Company that were sold by Fieldings Auctioneers Ltd. Whitefriars glass house was founded in 1815. In 1834 it was purchased by James Powel and run under the name of James Powel & Sons. The factory was relocated in 1923 to Middlesex and operated until its final closing in 1980.
Photos Courtesy of Fieldings Auctioneers
In the case of a bowl or vase below, the canes are in cased in clear glass. Then this assembly of canes and clear glass are worked into what ever shape that is to be made.
Modern Italian low quality
Millefiori Glass due to the complex manufacturing process, it is labor intensive and has a large glass waste associated, does not lend itself to large glass objects manufacturer.
The most common use of Millefiori Glass is in paperweights from the 18th century on. There are rare antique French examples of Millefiori glass objects in a non paperweight form. From the 20th century on most often of modern Millefiori glass vases, bowls and etc. are of Italian manufacture. They are not normally of a high quality and do not command high prices. Again the most common antique Millefiori Glass uses will be in paperweights from England or France.
Millefiori Glass History can be traced back to ancient Egypt about 1400 BC. This is about the time that Mosaic glass came into being. However ancient Mosaic is not truly Millefiori Glass. Production of molded and cast glass vessels dated back to the late Bronze Age in Mesopotamia and Egypt. Mosaic glass, in which slices of colored glass used to produce a decorative pattern was made in Egypt during the Ptolemaic period of Egypt. Blown glass was invented during the 1st Century by glassmakers of Syria.
The Persians were known to make and use glass mosaic beads in ornate jewelry around the first century B.C.E. Around 850 C.E., thick mosaic glass in Iraq had a bull’s-eye design and was used as floor tiles in the rooms of palaces. Mosaic beads were also found in tombs northern Iran, dating from the first to third century C.E.
Mosaic glass disappear with the fall of the Roman Empire and did not make a reappearance until the Middle ages. In Venice millefioris rods or canes were made and use to make vases and dishware. The modern glass that now carries the Millefiori name appeared during the 18th century in France and England in decorative paperweights. French companies such Clichy and Baccarat produced many Millefiori designs.
European glassmakers brought the Millefiori glass to the United States in the 19th century.
Mother of Pearl or MOP, (Mfg. Tech.): Mother of Pearl glass most often simple known as MOP it is more properly known as Air Trap Glass. It was first patented in England in 1857-58 by Benjamin Richardson. Joseph Webb of the Phoenix Glass works was granted a patented in the USA in 1886.
The method for manufacturing MOP requires molten glass being blown into a mold which has a designed pattern of projections built into the mold. This piece of glass when removed from the mold is then cased thus trapping air internally in the voids between the base glass and the case glass. This manufacturing technique creates the pattern. This type of MOP is sometime called “air trap MOP”. MOP is also normally found in satin glass which means it has been dipped in acid to create a satin finish.
Common patterns for MOP are Diamond Quilted and Herringbone also called "Ribbonette" or "Zig Zag". If you would like to learn more about MOP patterns see our links and follow the link to “Mother of Pearl, Common Patterns by Stu Horn.
Glass houses known to produce MOP include T. Webb & Sons in England, Phoenix and Mt. Washington in the USA and others including various Bohemia glasshouses. (Link to T. Webb Air Trap Glass), (Link to Air Trap Rose Bowl).
Nailsea Glass, (G.F. & Mfg. Tech. & ): Nailsea Glass is a type of glass which is both glass formula and manufacturing technique. It was also a village and a glass works in England in the from the 1700 until about 1874 when the coal supply ran out. After 1874 the term Nailsea Glass became a generic term for a specific type or style of glass. It was know to have been produced in Birmingham and Stourbridge. (Link to Nailsea Glass History)
Example of Nailsea Rose Bowl
Opalescent Glass, (G.F. heat reactive & Mfg. Tech.): There are three kinds of glass called Opalescent. The first type most common found on rose bowls is made when a base glass (clear, blue, green, cranberry, red, & yellow or Vaseline) is blown into a mold or some time free formed, it is then partially covered with a heat reactive glass. Next the rose bowl after receiving its coating is re-heated usually by returning the piece back into the "glory hole" furnace entrance and the coated area turns white. This heat reactive glass formula most often contained bone ash in the formula.
Rose bowls frequently only receives the opalescent glass coating on the crimp area or upper area of the rose bowl, other times a pattern coating is placed over the entire rose bowl.
Northwood, Dugan, Jefferson and other including Louis Comfort Tiffany were some of the manufacturers that made this type of Opalescent glass.
The second type of Opalescent glass is most often associated with press glass. It has a milky white edges or a white raised pattern decorating the piece of glass. This effect is produced when an entire piece of colored glass is made with a heat reactive formula. After the pressing process the glass as it starts to cool, is returned to the "glory hole" furnace entrance and the coated area nearest the heat turns white.
Many factories in the USA made this kind of opalescent glass during the period 1880 to 1920 including: Hobbs, Brockunier; American Glass; Northwood; Fenton; and others.
The third type of Opalescent glass is a blue tinged, semi-opaque glass or sometime clear with milky opalescence in its center, is made by both glass formulation and control cooling (slower cooling) certain parts of the glass object. This causes a structure difference, crystallization to occur in that part of the glass. Due to the structural difference it refracts the light causing a subtle golden color to appear when light is behind the object and shines through it. When light is in the front of the object it appears very different the golden color does not appear.
This type of glass has been manufactured by such famous maker such as: Lalique, Sabino, and Jobling's.
Examples of Opalescent Glass
Type 1 (Mixed: Northwood, Coudersport & Jefferson Rose Bowls)
Optics in glass Internal and External, (Mfg. Tech.) Optics is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. Optics in glass making terms are changes made to normally Brilliant Glass to enhance the light reflecting and or refracting nature of a piece of glass. However, Internal Optics are at times used on colored glass. By slight manipulations of the glass during manufacturing process Internal Optics are produced within the glass which create more sparkle or even a shading effect, (as an example internal ribs or bands). Internal Optics can be in the form of ribs, waves or grooves that are formed into molted surface of glass then reheated or covered so as to become a structure within the glass. One type of this is overshot glass. External Optics, is a structure on the external surface of the glass, to create light play these include glass such as Coin Spot, Hobnail, Bull’s Eye, Swirl and etc. Some external optics become more design pattern that optic.
Example of Internal Optic (left Dugan, right unknown Mfg. & below Jefferson)
Example of External Optic (Dugan)
Example of a combination of Internal & External Optic in one Rose Bowl (Model Flint - Reverse Swirl)
Peachblow, (G.F.): As per Johanna Billings, there are three distinct types of Peachblow. One, “Wheeling Peachblow” originally called Coral which was produced by Hobbs, Brockunier of Wheeling, WV. It ranges from a deep red brick color at the top and shades to golden yellow at the bottom. Wheeling Peachblow was made in both gloss and matte finish and always has a creamy white lining. Wheeling Peachblow is the only one of the three to be lined.
The second Peachblow was manufactured by Mt. Washington Glass Company and was called “Peach Blow” or “Peach Skin”. Mt. Washington’s Peachblow colors range from rose pink at the top and shades to blue-gray at the bottom. It was also made in both gloss and matte finish. However, it is never lined.
The third form of Peachblow is New England Peachblow it ranges from rose pink at the top and shades to white at the bottom. It was produced in gloss and matte finish and also was never lined. It was sold under the name “Wild Rose” the internal factory name was simply “Peach Blow”.
Peloton Glass, (Mfg. Tech.): is it is an ornamental glass which was made in Bohemia in the late 19th century. It also appears to have been made in England as well and latter in Czechoslovakia and the USA in the 20th century.
It is distinctive due to having glass threads, filaments or fine rods over a pastel based glass. We struggle to describe the rod like pieces of glass because they are larger than the glass threads or filaments used by Stevens and Williams and smaller the glass rods. They are most similar to the smallest glass rods, such as used in Milliefolori. These small thin rods are normally called canes. Glass canes of different colors are applied to the piece. They may or may not then be over cased in clear glass.
There are two possible manufacturing techniques available for the cane application. The first, most efficient and most likely used technique is similar to frit glass. Molten glass is gathered, blown and rolled into a rough cylinder shape. The molten glass cylinder is then rolled in the glass canes on a marver, in the same manner as the Frit Glass. Except with Frit Glass, the glass is crushed and / or powdered rather than being the canes. (See Frit Glass Above)
After the glass canes are rolled on the molten glass cylinder, the work is returned to the Glory Hole and reheated. The glass canes are then melted in. After the reheat it would be removed from the Glory Hole, if it was not to be clear cased, it would be blown into a mold, then it would be crimped and placed into the annealing oven.
If the piece was to be cleared cased, it would dipped in clear glass then blown, crimped and annealed.
A reported alternative method of applying the glass canes to the molten glass cylinder was to throw the canes on the glass then reheated. This would not be a very effective method and it would waste glass canes. Glass canes were made by hand by pulling glass. This method was probable not widely use, if at all. (Future Links to Peloton Glass examples)
In regards to the history of Peloton Glass there has been much misinformation published about its invention. As an example, it was supposedly patented by Wilhelm Kralik of Neauwelt, Bohemia on October 25, 1880. In has also been falsely reported that he was working for Count Harrach, the owner of one of the largest Glass Houses in Bohemia at the time.
Records indicate that Count Harrach ceased from managing the glass works in 1778 while still maintaining ownership. As per Ms. Truitt, Antonin Erben managed the works until his death in 1795. At which time Martin Kaiser took over and managed the works until 1808.
One other slight problem is that Wilhelm Kralik died in 1877. Josef Meyer acquired four glass houses: Adolfshutte, Kaltnebach, Idathal and Volynka between (1816 – 1829). Jan Meyr, Josef Meyr son worked in the business and improved operations by adding cutting and engraving shops. Jan, inherited the business upon his father’s death. Then Jan died childless in 1841 at the age of 61.
In 1841 his father’s company’s ownership, passed to Jan’s nephews Josef Taschek and Wilhelm Kralik. In 1854 they acquired two more glass works: Ernsbrunn and Franzenthal. The firm’s name was then changed to J. Meyr’s Neffen (the nephews of J. Meyr). In 1851 Wilhelm Kralik married Louise Lobmeyr the sister to Josef Lobmeyr the founder of J. & L. Lobmeyr a glass retail store in Vienna
Josef Taschek died in 1862, leaving Kralik in total charge of his own firm. He changed the company name to Meyr’s Neffe at that time. Kralik was a glasshouse owner from 1841 until his death in 1877. Thus he was not working for Harrach.
Upon Kralik death his four sons inherited the Kralik firm of Meyr’s Neffe. The firm consisted of six glasshouses which was divided between his four sons. As per Ms. Truitt, Karl and Hugo inherited; Adolfshutte, Idahutte, Luisenhutte and Franzhutte. Karl and Hugo ran their business under the name “Meyr’s Neffe” which was Kralik’s company name from 1862 on.
Kralik sons Heinrich and Johann inherited two glasshouses being Eleonorahutte and Ernsthutte. They operated their business under the name “Wilhelm Kralik Shone” (sons)
Hugo died in 1883, Karl died in 1899. Karl’s sons Alfrons (1885-1962) and Siegfried (1891-1974) inherited the firm of Meyr’s Neffe which operated until 1922 when it merged with Ludwig Moser and was renamed A. G. Ludwig Moser & Sohn und Meyr’s Neff A.G.
The firm of Wilhelm Kralik Shone remained in business up until the beginning of WWII.
We can safely assume that Wilhelm Kralik did not patent the glass in 1880 while working for Harrach. If a patented was issued in 1880 it would have most likely been to firm of Wilhelm Kralik Shone. Thus far we have not seen a patent. We are searching for a copy of said Patent.
Pulled Glass, (Mfg. Tech.): Pulling is a glass manufacturing technique some times also called “swung”. To swing glass, the glassmaker retrieves a piece such as a short vase from the mold; he then places it in a "snap," which is a metal rod with jaws that hold the piece's base. He reheats the glass and then swings the rod back and forth or twirls it, causing the glass to twist or increase in length. Many varieties of old glass were subject to swinging: swung vases, for example, may be found in carnival, EAPG, opalescent and even stretch glass.
An example of machine Pull Glass made be Stevens and Williams.
Photo Courtesy of Fielding Auctioneers Ltd.
Rose Amber Glass, (G.F. heat reactive & Mfg. Tech.): See Amberina - heat sensitive.
Rubena Verde, (Mfg. Tech.): Rubena Verde in Italian means “ruby green”. In terms of glass it describes glass that shades from red on the top to green on the bottom. According to the Collector's Encyclopedia of American Art Glass, 2nd ed., “the red of Rubena Verde ranges from dark ruby-red to pinkish-red cranberry; the green may be a dark, almost aqua green to yellowish green”.
American Rubena Verde was both press and mold blown. In the 1880's, United States glassmakers such as Hobbs, Brockunier & Co., used uranium oxide as a colorant in Rubena Verde, producing mold-pressed glass that faded from ruby to the yellow-green color now known as "canary" or "Vaseline". Rubena Verde coloring was often produced in blown glass through a casing technique: a gather of molten red glass was placed on a larger green or Vaseline gather. As the two colors were blown together, the red glass remained near the rim of the glass piece formed. Rubena-Verde pieces made with uranium-content glass fluoresce brightly under black light.
An example of Rubena Verde Rose Bowl
Photo courtesy of Stu Horn
Ruby Glass, (G.F.): Ruby Glass is a deep red glass made with gold chloride. See glass colors gold chloride and Selenium.
Ruby glass has ancient roots in ancient Roman. Whose craftsmen made a bright, blood-red glass by mixing molten glass with minute spheres of gold. The process for making what was called "gold ruby" glass was rediscovered by Johann Kunckel of Berlin in the mid-1600. He dissolved gold in Aqua Regia (nitric acid and hydrochloric acid), producing gold chloride. He then added the gold compound to molten glass; when the glass was reheated, the gold chloride caused it to turn a deep ruby color. By the 1800's, such glass was referred to in Victorian England as "ruby glass".
This second form of ruby glass is sometimes called "selenium ruby". Although produced by Steuben, selenium ruby's discovery is credited to Nicholas Kopp, the Chief Scientist for the Pittsburgh Lamp, Brass and Glass Co., who developed the selenium glass process in the 1890's; one of selenium ruby's first uses was in railroad signal lights.
Ruby Amber, (Mfg. Tech.): See Rubena Verde. Ruby is plated over Amber glass.
Satin Glass, Mfg. Tech.): is the name for any glass that has been chemically treated to give it a satin finish. The term "satin glass" is frequently used to refer to certain types of acid treated glass, historically in the case of art glass either pressed, blown into a mold and free blown glass.
The satin finish typically is produced by treating the glass by immersion in hydrofluoric acid or exposure to hydrofluoric acid fumes.
In the 19th century the process was synonymous with "frosting" and was a technique associated especially with the fancy art glass of the Victorian period. Satin glass was supposedly made first in England as decorative glass and latter in the U.S. during the late 1880s. Satin glass during the Victorian period was made by almost all the American glass companies which produced colored glass, in addition to the English glasshouses and also numerous glasshouses on the European continent.
During the Victorian period the translucent quality of Satin Glass lent itself to its use in the production of kerosene lamp shades as well as art glass. Satin glass continues to be produced today in art glass forms as well as commercial use as frosted electric light bulbs.
Silveria, Made by Stevens and Williams only (Mfg. Tech.) is an embedded foil technique but not Burst Foil:
There appears to be confusion in properly identifying Stevens & Williams “Silveria” vs. Kralik’s “pseudo Silveria” and differentiating both from the Bust Foil Technique glass. “Silveria” was only produced by Stevens & Williams and no other glasshouse.
Let’s first look at the appearance differences below:
Stevens & Williams' Silveria vs. Kralik’s pseudo Silveria and Burst Foil
S & W Kralik
The invention of Silveria was due to John Northwood II, continuing the pioneering work of his father. He developed Silveria in 1900. Silveria glass is a colorful but abstract design in various physical shapes, made by sandwiching silver foil between two layers of glass. The glass may be clear or colored or with trails of color. Silveria is usually marked with “S&W” and “England.”
John Northwood’s health began to fail in 1901. Frederick Carder was then appointed chief designer for S&W. This marked the end of what is known as Stevens and Williams “Fancy Period.” John Northwood died in 1902 at the age of 65.
In regards to Burst Foil technique, Edward Webb and Joseph Webb both had produced their own versions in 1883, long before S&W produced Silveria in 1900. Stevens and Williams' Silveria differed from Webb's foil work since the silver foil remained intact, rather than breaking into fragments. Broken fragments of foil which are sandwiched between layers of glass are known as the “Burst Foil Technique”, not Silveria.
There are many different types of embedded foil work of which Burst Foil is the most common and there are famous examples of it by Edward Webb’s 1883, “Oroide and Agrentine”. He advertised the use of gold or silver foil between two layers of glass, respectively. Arthur John Nash was responsible for both designs.
Kralik also made a glass to compete with Stevens and Williams’ Silveria. Kralik’s version appears similar to the eye, but to my understanding it was produced in a frit glass and marver technique with a white powder in place of the normal crushed glass. No foil was ever used.
Below you will find some information which may be helpful to the reader to properly identify S&W’s Silveria, from Kralik pseudo Silveria and Burst Foil glass. I don’t mean to over state the obvious but look at the three examples above, to visually see the differences in S&W’s Silveria, Kralik’s pseudo Silveria and Burst Foil glass. Once you have visual compared the examples, they are easily identified. At the end of this section the reader will find a several documented examples of S&W’s Silveria and a detailed side by side visual comparison of S&W Silveria and Kralik’s pseudo Silveria for your reference.
The first thing you should note is the S&W Silveria, is an Embedded solid foil technique sandwiched between two pieces of glass, NOT a powder glass or other coating applied using the Frit Glass technique, nor is it a Burst Foil technique. The Kralik pseudo Silveria is powder coating which used the Frit Glass technique. For those of you not familiar with Frit Glass or Burst Foil technique, please see Frit Glass or Embedded Foil Glass.
The second point is the glass (threading, trailing, or random glass rods) which s are a glass overlay on the outside surface of the piece glass, runs predominantly VERTICLE on Stevens and Williams pieces of glass and HORIZONTAL on Kralik glass.
Third, you will almost always see some burn through on all of the real S&W Silveria glass but not the Kralik because there was no foil used. It is common to find burn through on the bottom but it is also found on the side of the Silveria glass too. (See the detailed side by side visual comparison of S&W Silveria and Kralik’s pseudo Silveria below.)
Fourth, S&W Silveria is usually marked with “S&W” and “England.”
Click on the (Silveria Photo Link) to be take to Know examples of Stevens and Williams Silveria Glass and examples of a side by side visual comparison of S&W Silveria and Kralik’s pseudo Silveria.
Slag Glass, (Mfg. Tech.): Is a collectors name for an opaque pressed glass which contains streaks of other colors. The streaks are usually white and or cream colored. This name was not used by glass makers until recent times. When this type of glass was originally produced it was called "Marble Glass", "Brown Malachite" or "Brown Marble Vitro- Porcelain". Slag glass in commonly found in purple, less common in blue, brown and green.
In the North East of England during 1880 through the 1890 large amounts of this kind of glass was manufactured by all of the pressed glass manufacturers. These included companies like Sowerby, Greeners and Davidson's.
In the USA in addition to Akro Agate, slag glass was made by Imperial Glass and by Westmoreland Glass as well as several other companies. It is still popular today and still made in the US and in Europe. It is made in a wide range of colors today including red and orange.
Example of Slag Glass
Spangled Glass, (G.F. & Mfg. Tech.): A US Patent #292,663, was received on January 28, 1883, by William Leighton, Jr. of Hobbs, Brockunier & Co. for “having invented or discovered “new and useful Improvements In Manufacture of Spangled Glassware”. Hobbs neither invented nor discovered Spangled Glass; he only claimed to have improved the manufacturing of it.
Under his patent for Spangled Glass: it was produced by being “Ornamented by spangles or flakes of high crystalline material covered by a superimposed lay or layers of glass”. It continues by stating “I incorporate into the substance of the glass, while the same is a plastic condition [molten] a series of spangles, flakes or fragments of infusible crystalline material, and thereafter blow the glass in the usually manner. I have in practice effectively and conveniently conducted the operation by gathering from the melting-pot a ball of glass, and rolling it , while still hot upon a marver, over the surface of which are spread, in such relative arrangement as may be desired, flakes of colorless infusible crystalline material—such as mica—which I have found most desirable for the purpose. These flakes, which, to produce the best effect in the finished article, should be very thin and of irregular size shape and disposition, (although they may be uniform in those particulars, if preferred,) will in the rolling, adhere to the hot glass. The ball with the adhering flakes is then returned to the pot, and an additional layer of glass, of any desired color, is gathered upon it. The ball of glass thus formed is then blown in the usually manner, into any desired shape and the flakes, being destitute of color, and acquiring, by the action of the heat considerable opacity, assume, by their reflective power, the tint of tints of the superimposed glass.” “The ball, after being flecked with crystalline material, may be coated more than once with glass, if desired or may receive platings of different colors.”Upon review of William Leighton, Jr. Patent #292,663, it would appear he received a patent for an already known Frit Glass and Marver techniques and was infringing upon parts of William Boulton’s of Boulton and Mills, early English Patent dated 1879 for Vasa Murrhina Glass.
Spatter Glass, (Mfg. Tech.): Spatter Glass is probably best described as a collection of different colored, larger glass pieces, which can be regular or irregular in shape that are melted together then worked into a desired shape. Spatter Glass was produced in transparent, opaque and cased glass forms. Well-known examples of Spatter Glass included H. Northwood’s Royal Ivy #287, Aurora #285 (latter called Hobbs Optic) Leaf Mold #333 and Mt. Washington’s Lava Glass. Note: Northwood’s Aurora and Leaf Mold can be found containing gold or silver flecks, in which they become Spangle Glass, not Spatter Glass.
Peloton Glass can be considered a subset of Spatter Glass. Peloton Glass is normally cased glass where the pieces of glass attached to the opaque case core are thin rod shaped pieces, which are coated with a clear glass. The thin rods may be transparent, opaque or a combination.
Tortoiseshell Glass can also be considered a subset of Spatter Glass since it consists of two transparent layers of glass encapsulating core pieces of brown glass.
Aventurine Glass, Vasa Murrhina Glass, Spangle Glass and various forms of English foil contained glass are not forms of Spatter Glass. While they may share similar frit glass and marver techniques, they contain metals that do not melt at glass temperatures and flow or homogenize into the surrounding glass. In the case of Vasa Murrhina Glass, it must also be cracked and over coated with clear glass and this differs from Spatter Glass.
Spatter Glass Manufacturing: there are several methods for the incorporation of the glass bits and the re-melting of glass pieces. The most common form of Spatter Glass has irregular colored glass shapes (bits of glass) applied to a clear or colored, usually opaque white core (a gather), which is rolled over a hot marver, then reheated thoroughly in the glory hole and re-rolled. At this point, the molten gather is either blown into a spot mold or reintroduced into the glass tank for an overcoat of clear or colored glass. The glass is then blown into the desired shape.
The intention of Spatter Glass is for the larger bits of glass to melt and distribute an overall irregular colored pattern to the overall glass piece.
History of Spatter Glass: as indicated above, there are various methods to produce Spatter Glass. Spatter Glass has been produced off and on since Roman times. It was widely produced in the 18th and 19th centuries in England, Spain and France. Spatter glass has been made in Bohemia since the 1880s, and it reached a peak of popularity and output volume in the 1930s. There were many new designs in the 1920s which continued to be produced through the 1930s until the war with Germany caused massive disruption to the Czechoslovakian glass industry.
Several Patents have been issued in Europe and the US from 1880 onward. John Samuel Irwin received a US Patent #502,461 on August 1, 1893 for a “method and to means for making articles of glassware ornamented with variegated colors and to the article made.” Irwin’s method was considerably different than the more common frit/marver technique. Irwin placed pieces of “ornamental material” on the bottom of a heated metal pan or cup-like mold. He then poured molten transparent glass on top of the ornamental material, which was then pressed the together with a plunger. This colored piece was next removed and placed so the clear glass side was down, then a bottle top was attached to the bottom disk. Irwin’s technique leads us to the possibility of a simple re-melt of pieces of glass to make Spatter Glass.Spatter Glass has also been called Splashed Glass, End-Of-Day Glass, and Mottled Overlay Glass.
Example of Spatter Glass Rose Bowls
Stained Glass, (Mfg. Tech. with Chemical treatment): Staining as it name implies is nothing more that a chemical coating that is applied to glass which develops its color during a heat process. Annealed (cooled) glass has the chemicals painted on it, then it is re-fired to fix the color. Stained glass can be scratched rather easily.
This should not be confused with Stained Glass Windows which are normally made of pieces different colored glass in a lead glass frame, of which the color is formed during the glass formulation process and is consistent throughout the piece of glass. The read should be aware that some Stained Glass Windows are a mixture of color glass and stained glass as described above.
Stretch Glass - Iridized, (Mfg. Tech. with Chemical treatment): Iridized stretch glass is glass which has been re-heated after the Iridizing process. This causes the glass surface bonded to the iridescence to expand less than the glass beneath it thus the splitting the surface producing fine striations on the surface of the glass. These causes a shine matte appearance various standard shinny surface of normal iridized surface. This effect is sometime emphasized by re-working the glass with flaring, crimping or pulling on the edges.
This process was introduced in the USA about 1916. I was popular in the 20s and was made until the mid 1030s. The name Stretch Glass was not applied to this glass until much latter. This form of glass was produced by several companies including: Central Glass Works, Wheeling WV, Diamond Glassware Company, Indiana, PA., Imperial Glass, in Bellaire, Jeannette Glass, King Glass, Pittsburg, PA., Lancaster Glass, Northwood Glass, Wheeling WV, Tiffin Glass and Vineland Flint Glass Works.
Stretch Glass is typically produced from plain pressed glass, normally without surface decorations or patterns. Stitch glass is sometimes mold blown.
Stretch Glass sometime mistaken for art glass produced by Steuben or Tiffany.
Threading Glass, (Mfg. Tech.): The Corning Museum of Glass, defines threading as "the process of winding a thin trail of glass around an object to create the appearance of parallel lines". A "trail" is a strand of glass. In 1876, W. J. Hodgetts of Stourbridge, England, patented a machine that produced closely-spaced glass threading; such threading is shown in the photographic detail of the nineteenth century threaded vase immediately above. An Illustrated Dictionary of Glass notes that the term "threading" may be used in two ways: (1) to describe glass threads applied as independent decoration onto a glass object, (rather than being incorporated into its surface); and (2) to refer to the process of drawing glass threads through molten glass as a means of decorating it. The term "trailing" is sometimes used interchangeably with "threading".
Example of Thread Glass Rose Bowl (Northwood) (Direct Link)
Tortoiseshell Glass, (Mfg. Tech.): Tortoiseshell Glass is an art glass in which two layers of blown glass have pieces of brown glass trapped between them. The brown glass is usually in two colors, light and dark brown and shaped in blotches to resemble the marking on a tortoise shell ergo the name.
Tortoiseshell Glass can also be considered a subset of Spatter Glass since it consists of two transparent layer of glass encapsulating the core of irregular pieces of brown glass.
The original patent for this glass was registered in London by Francis Pohl and S. A. Wittman on October, 25, 1880. Pohl and Wittman were from Europe where they most likely learned how to make Tortoiseshell Glass. Prior to their English Patent Tortoiseshell glass was made in Germany.
Their patent described the process of first blowing bulbs of brown glass, one dark and one lighter, and after cooling they were broken into fragments. The light and dark fragments were placed onto a hot marver (a heated steel or iron plate). A clear transparent gather was collected from the glass pot and blown to increase its size; then it was rolled over the light and dark brown fragments on the hot marver. The infused gather was most likely reheated in the Glory Hole. After reheating the pieces could be further shaped, then dipped into a clear tank of molten glass for the overcoat. This is the simplest method.
A second method (reported by other authors and not historically supported thus far) could also have been employed as follows: after a second bulb of clear glass was blown, the top was then removed to allow the first bulb with the brown pieces of glass attached to it to be inserted inside the second bulb. The two bulbs were joined and then blown into the required shape. The final product was then coated with a yellow stain before firing and annealing. This is the most complicated method but it produced a beautiful type of art glass. Many improvements were made as an example, the yellow staining was not needed if second re-coat of glass was of a pale honey gold color.Tortoiseshell Glass was known to have been made in Europe. As per John A. Shuman III, in his book American Art Glass second Edition; Tortoiseshell Glass was also produced by the Boston and Sandwich Glass Co. in Massachusetts. We are also aware the “Tortoiseshell” was also a name sometimes used for pressed glass with an amber background and darker brown streaks.
An Example of Tortoiseshell Glass and not the best example.
Uranium Glass, (G.F.): See Vaseline Glass.
Vasa Murrhina Glass, (G.F. & Mfg. Tech.): Vasa Murrhina Glass is a type of glass with a transparent overlay of glass in which pieces of colored glass and mica flakes are embedded. The process was submitted for patent in England in 1879 by William Webb Boulton and his partner Fredrick James Mills of Boulton and Mills - Audnam Glassworks.
This process is very similar to frit glass in which colored glasses or enamels, powdered or crushed, are spread on a marver. Then a gather of glass is rolled in this powder while in a semi-molten state and may be plunged into water and cracked. Next it is reheated, blown into a mold, pressed or cut as normal. Finally, a thin layer of flint is placed on the surface of the glass object.
Vasa Murrhina glass is sometime incorrectly confused with Aventurine glass. Vasa Murrhina has mica flakes and colored glass embedded in a frit glass technique, while Aventurine has metallic copper particles which are suspended or incorporated in a flame reduction process.
There is also the English embedded foil techniques used by Edward Webb and Joseph Webb as well as Steven Williams, both differ from Vasa Murrhina and Aventurine glass.
Arthur John Nash was the Works Manager for Edward Webb, Jr. Nash was responsible for many of the new designs created at White House Glassworks. In 1882, Nash patented Vasa Murrhina glassware. However, William Webb Boulton’s patent, of Boulton & Mills, predates Nash’s 1882 patent. In 1883, the firm of Edward Webb advertised the use of gold or silver foil between two layers of glass called Oroide and Argentine, respectively. Nash was responsible for both designs.John Northwood II continued the pioneering work of his father by developing Silveria in 1900. Silveria glass is a colorful but abstract design. It was made by sandwiching silver foil between two layers of glass. The glass may be clear or colored or with trails of color. Silveria is usually marked with “S&W” and “England.” Edward Webb and Joseph Webb both had produced their own versions in 1883. Stevens and Williams' Silveria differed from Webb's foil work in that the silver foil remained intact rather than breaking into fragments.
Example of Vasa Murrhina Glass Rose Bowl
Vaseline Glass, (G.F.): Vaseline glass is not a historically correct name. The originally name for this type of glass was called Canary or simple Yellow glass. The term Vaseline was coined by antique dealers to describe their wares. Many times today the term Vaseline Glass is indiscriminately used to reference any glass that glows under black light. True Vaseline Glass (American Term will be Yellow (Canary) to Green or any shade in between, it must be transparent and made with about 2% Uranium oxides. It must also fluoresce under black light. True Vaseline Glass must meet all of the above conditions because color alone is not proof. We can make yellow green glass from traces of iron impurities in the sand used to make the glass. There are other metals that glow under black light. As an example clear glass containing Manganese will fluoresces.
The term used in England is “Uranium glass” which includes everything defined under the American Term “Vaseline” plus things like Custard and Burmese glass that also contains uranium sulfite and or other uranium sulfides as coloring agents. These types of glass are opaque.
Examples of Traditional Vaseline Glass Rose Bowls
Example of Custard Glass Rose Bowl (Uranium Glass)
*2 Truitt, Robert & Deborah, Mary Gregory glassware, 1880-1980, Kensington, MD: B&D Glass, 1992
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