Definitions of: pigeon blood glass - polished glass - pontil - pressed glass - pulled glass - purpled glass - Pyrex
GLOSSARY OF GLASS TERMS
Pi - Pz
The purpose of this guide is to help buyers understand terms
commonly used by E-Bay sellers to describe old American glass (1850-1925).
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Many thanks to all the E-Bayers who
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A Victorian pigeon blood tankard pitcher
with enamel decoration and an applied handle
photos courtesy of nickadaemous
Pigeon blood: a color of glass. "Pigeon blood" is defined in John Shuman's The Collector's Encyclopedia of American Art Glass, 4th ed., as "a brilliant ruby glass with brown highlights". Although it is correct to use "pigeon blood" interchangeably with the term "oxblood," you will see the term "pigeon blood" used most commonly to describe old pressed glass that has a solid deep red color, such as the pitcher shown above. When held to light, the deep red of such pigeon blood glass has an orange cast. Pressed pigeon-blood glass was especially popular in the United States during the 1880's and 1890's. Pieces were made with both shiny and satin finishes, and were issued in a variety of forms -- in silverplated frames with mold-pressed patterns; with plain, scalloped and beaded edges; and, as shown above, with enamel decoration. According to Shuman, commonly seen patterns in pressed pigeon blood glass are Hobnail, Bulging Loop, Torquay, Diamond Quilt, Fine Rib and Vertical Rib. Among the most prominent makers of pressed Victorian pigeon glass was Consolidated Lamp & Glass Co. of Coraopolis, Pennsylvania. The name "pigeon glass" borrows from the old lapidary term used to describe the highest quality of color in rubies -- the intense, dark red jewelers call pigeon blood. Compare "ox blood" in this glossary.
Polished glass. Polishing is a glass finishing technique. Polishing, according to An Illustrated Dictionary of Glass, is "The process of giving glass pieces a smooth brilliant surface after an object has been cut or engraved. The first step is with a fine-grained stone rotating wheel, then with a finer wheel of lead, wood or cork and the use of putty powder on a brush." Fire-polishing is a distinct process. Fire polish, according to the same source, is "the brilliant surface condition given to glass by heating at the mouth of the furnace after the manufacture of a glass object." Fire polishing is used to to smooth irregularities in the glass surface; to polish mold seams as a finishing effect; to polish pontils; or to remove the dull surface sometimes imparted to pressed glass from the iron in molds.
Detail photos of a rough pontil on an Art Nouveau vase forgery (left)
and a smooth pontil on Victorian cranberry glass (right)
photos courtesy of curculiosglass
Pontil: an attribute of blown glass. When blown glass pieces are made, they are attached to a rod held by the glassmaker called a "pontil rod". The pontil rod is usually four or five feet long, with a dab of molten glass on the end; this sticks to the bottom of a hot glass piece as it is formed, allowing the glassmaker to manipulate the glass. When the finished glass is snapped off the pontil rod, this leaves a rough spot, usually on the base of the glass, called a pontil (or a punty or pontil mark). A rough pontil is the term used for the unfinished spot before it is polished (shown above, left). A rough pontil also may be called an open pontil. A smooth pontil is the term applied to the rough area after it is ground, leaving a circular depression (above, right). A smooth pontil is sometimes referred to as a ground pontil. Smooth pontils also may be polished: this means that a rough pontil was ground and the pontil area then highly polished to neaten the original pontil mark . Smooth, polished pontils are often found on expensive glassware. The presence of a pontil of a particular kind sometimes helps establish the age or authenticity of an antique glass piece. For example, rough pontils on signed Tiffany's Favrile vases and on signed Steuben glass are usually an indication that the signatures are forged and that the glassware is fake. Similarly, forgeries of Burmese and Peachblow glass often have rough or only partially ground pontils (below right). Genuine Victorian Burmese and Peach Blow pieces should bear smooth polished pontils; on satinized pieces, the pontil may be polished first and then satinized with the rest of the piece, so that the remaining pontil mark is subtley visible (see below, left). (See also, "Burmese" and "Peachblow" in this glossary. And see "Steuben glass" and "Tiffany glass"). Special note on bottles: Pontils are especially important in the dating and authentication of old bottles -- and old bottles feature a broad array of pontil types. An excellent resource on bottle pontils is the Historic Glass Bottle Identification and Information Website (sha.org/bottle/pontil_scars.htm#Top).
A satinized smooth polished pontil on genuine Mt. Washington Burmese (left):
and a Burmese knockoff whose pontil is only partially ground (right).
photos by gljacobsct (left) and curculiosglass
Pressed Glass: pressing is a glass-making technique. According to An Illustrated Dictionary of Glass, pressing is the making of glassware by shaping it, while molten, in a metal mold. The mold forms the shape and outside pattern of the piece, which is then pressed inside with a metal plunger that forms the inner shape and pattern. "Pressed glass" is also called "mold-pressed glass". American carnival glass and EAPG are both varieties of pressed-glass. The Victorian opalescent vases shown below are also examples of pressed glass. For wonderful photographs of what a metal glass mold and plunger look like, visit the website of the renown carnival glass authority, David Doty (see "How Carnival Glass Was Made," at this url: ddoty.com/howmade.html). For further information, see "mold-pressed" in this glossary.
Opalescent Heatherbloom vases made by Jefferson, circa 1905:
the vase on the left has been swung, or pulled into a taller shape.
photos courtesy of curculiosglass
Pulled glass, or swung glass: pulling is a glass-making technique. You may read descriptions on E-Bay that say that a piece of glass such as a vase was "pulled" to make it taller than the original mold. Another term for this is "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. The blue Heatherbloom vase shown above was swung or "pulled" from the same mold as the white vase to its right; both have the same size base. Swinging often distorts a pattern -- in Heatherbloom vases, for example, swinging may so distort the pattern that it is difficult to identify.
Two examples of purpled glass: the compote at left is the gentle lavender hue
that old colorless glass may take on if exposed for prolonged periods to sunlight.
The insulator at right has been "nuked"-- that is, its deep purple coloring was induced
through exposure to artificial irradiation from a germicidal ultraviolet light.
left photo courtesy of kevincrespi9911
Purpled glass: colorless glass that has turned purple. Purpled glass also goes by the names sun-purpled glass, solarized glass and desert glass. Purpled glass is transparent, colorless glass that has turned lavender or purple as a result of prolonged exposure to the sun's ultraviolet rays or to an artificial source of ultraviolet radiation. The Corning Museum of Glass explains this process as follows. An essential ingredient of glass is silica, which glassworks generally derive from the mineral quartz in sand deposits. Although silica is colorless, mineral impurities can impart color to raw glass; iron, for example, which is usually present in silica sand, tints glass green. Glassworks add decolorizers to molten glass that neutralize the colorizing effects of such mineral impurities. The most common decolorizer is manganese dioxide, which oxidizes iron impurities in glass, turning the glass colorless while simultaneously undergoing a chemical reaction that renders manganese colorless. After a glass piece is finished, however, the glass's manganese content can react over time to sunlight. If a decolorized glass piece is exposed to the sun's ultraviolet radiation for long periods, the manganese becomes "photo-oxidized," and is converted back into an oxidized form that imparts a pink or lavender color to the glass. The compote in the photograph above left is an example of old glass that has taken on the gentle lavender associated with exposure of decolorized glass to sunlight. The Corning Museum of Glass notes that common examples of purpled glass are bottles, insulators and "the famous purplish windows on Beacon Street in Boston and the little circular glass disks sometimes found in sidewalks of older parts of cities." The name "desert glass" comes from a practice once in vogue in desert states, which entailed leaving old glass in the sun in order to produce lavender coloring in the glass. Purpling also may be produced artificially. Dealers wishing to make clear glass "look antique" have been known to place it under a germicidal black light, which produces intense ultraviolet radiation that can turn glass fairly quickly to a shade anywhere from lavender to the deep purple exemplified by the insulator shown above right. Such artificially irradiated glass is sometimes referred to pejoratively as "nuked glass," and is generally viewed dimly by collectors of 19th Century glass. EAPG groups such as patternglass.com ask dealers not to engage in intentional purpling, because it damages scarce old glass. According to some glass experts, the process of purpling is irreversible. This is not strictly true, however. Exposure to high levels of heat will reverse purpling effects on glass. Glass insulator collectors frown on this procedure and refer to it as "cooking". According to the National Insulator Association, "During the thermal reversal or 'cooking' process, the manganese is once again the key stimulant. In most cases, when a sun 'purpled' insulator is heated to high temperatures, generally a step below melting, it will revert back to a shade in close proximity to its original manufactured color" (see nia.org/altered/). Presumably, insulators are likely to withstand "cooking" better than fragile old EAPG ware might. Buyers should note that old glass such as EAPG is considered more valuable when colorless than when purpled. Thus, colorless EAPG glass should not be kept in a sunny place. Recommended Resources: For an interesting article on artificial purpling, visit patternglass.com (patternglass.com/this_color_purple_99.htm). If you would like to read more about how purpling works, visit the websites of the National Insulator Association (nia.org/altered/) and the Corning Museum of glass (cmog.org/index.asp?pageId=747).
A 1916 Corning Glass advertisement for Pyrex
announcing "A new material has come into the world."
Pyrex: a kind of glass. According to An Illustrated Dictionary of Glass, Pyrex is "the well-known trade name for heat-resistant oven-glass made by the Corning Glass Works and its world-wide licensees. It is made with borax and technically called 'borosilicate glass'." Pyrex was perfected in 1915 by W.C. Taylor and Eugene Sullivan (of Corning Glass), in their effort to produce glass that could resist the heat-shock that caused railway brakemen's lanterns to crack when exposed to rain or snow. As early as 1916, Pyrex was used to make a variety of baking dishes. The above Corning Glass advertisement from a 1916 Literary Digest proclaims: "By means of this modern discovery food is now baked in transparent glass dishes so durable that the hottest oven will not break them". Pyrex was issued in a dazzling array of patterns and shapes and is now widely collected. A stupendous website resource for identifying Pyrex patterns is The Pyrex Files (dragonfire1.50megs.com/Pyrex/Pyrex.htm).
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Many thanks to E-Bayers gljacobsct, kevincrespi9911 and nickadaemous, for generously contributing their expertise and photographs to this page of the glossary. Rights to all photos belong to the photographers, and pictures should not be used without their permission. Text is (c) 2007 curculiosglass, all rights reserved. To locate any E-Bay seller mentioned here, just click on "Site Map" at the bottom of your E-Bay screen, and then click on "Feedback Forum" at the right top corner of the large menu that pops up. Type or copy the seller's name into the Feedback Forum's search blank.
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