Corning Museum of Glass

Historically, the most common form of glass. It contains three major compounds in varying proportions, but usually silica (about 60-75 percent), soda (12-18 percent), and lime (5-12 percent). Soda-lime glasses are relatively light, and upon heating, they remain plastic and workable over a wide range of temperatures. They lend themselves, therefore, to elaborate manipulative techniques.

A mold with the same shape as the desired object, usually a vessel. Flat glass blanks are made into vessels by sagging them over or into former molds.

The process of reheating a blank until it becomes soft and gradually flows under its own weight over or into a former mold and eventually assumes the shape of the mold. Soda-lime glass becomes soft at about 1110°F (600°C). Slumping is also known as sagging.

The process of reheating a blank until it becomes soft and gradually flows under its own weight over or into a former mold and eventually assumes the shape of the mold. Soda-lime glass becomes soft at about 1110°F (600°C). Slumping is also known as sagging.

Any cooled glass object that requires further forming or decoration to be finished.

Sodium carbonate. Soda (or alternatively potash) is commonly used as the alkali ingredient of glass. It serves as a flux to reduce the fusion point of the silica when the batch is melted.

A form used for shaping and/ or decorating molten glass. Some molds (e.g., dip molds) impart a pattern to the parison, which is then withdrawn, and blown and tooled to the desired shape and size; other molds (sometimes known as full-size molds) are used to give the object its final form, with or without decoration. Dip molds consist of a single part and are usually shaped like beakers. Full-size molds usually have two or more parts and can be opened to extract the object. Nowadays, most molds are made of metal, but stone, wood, plaster, and earthenware molds were used in the past and are still occasionally employed today.

Calcined limestone, which, added to batch in small quantities, gives stability. Before the 17th century, when its beneficial effects became known, lime was introduced fortuitously as an impurity in the raw materials. The addition of insufficient lime can cause crizzling.

(1) A rounded, hollow vessel; (2) the uppermost part of a goblet, tazza, or wineglass.

(from French salière, “salt dish”) A small bowl used at the table for salt.

A tray for serving. At first, salvers were used primarily for presenting objects to rulers. More recently, the word is used to denote trays used for presenting letters or visiting cards, or for serving refreshments.

Silicon dioxide, a mineral that is the main ingredient of glass. The most common form of silica used in glassmaking has always been sand.

The mixture of raw materials (often silica, soda or potash, and lime) that is melted in a pot or tank to make glass. Cullet, as well as minor ingredients such as colorants, can be added to the batch to help the melting process.

The most common form of silica used in making glass. It is collected from the seashore or, preferably, from deposits that have fewer impurities. For most present-day glassmaking, sand must have a low iron content. Before being used in a batch, it is thoroughly washed, heated to remove carbonaceous matter, and screened to obtain uniformly small grains.

The technique of forming a vessel by winding or gathering molten glass around a core supported by a rod. After forming, the object is removed from the rod and annealed. After annealing, the core is removed by scraping.

A non-shiny finish made by grinding, sandblasting, or exposing the surface to fumes of hydrofluoric acid.

(from Italian, “engraving”) A method of wheel engraving whereby the ornamentation is cut into the object and lies below the surface plane. The German name for this technique is Tiefschnitt.

Changes on the surface of glass caused by chemical reaction with the environment. Weathering usually involves the leaching of alkali from the glass by water, leaving behind siliceous weathering products that are often laminar.

(1) The process of founding or melting the batch; (2) heating pieces of glass in a kiln or furnace until they bond (see Casting and Kiln forming); (3) heating enameled glasses until the enamel bonds with the surface of the object.

(Italian, “chalcedony”) Glass marbled with brown, blue, green, and yellow swirls in imitation of chalcedony and other banded semiprecious stones. Calcedonio was first made in Venice in the late 15th century.

(1) The application of a very thin layer of glass of one color over a layer of contrasting color. This is achieved by dipping a gather of hot glass into a crucible containing hot glass of the second color. The upper layer may be too thin to be worked in relief. “Flashing” is sometimes used (erroneously) as a synonym for casing. (2) The act of reheating a parison by inserting it into a glory hole and then withdrawing it rapidly.

A layer of glass that covers a layer of a different color, often as the result of casing or flashing.

A vitreous substance made of finely powdered glass colored with metallic oxide and suspended in an oily medium for ease of application with a brush. The medium burns away during firing in a low-temperature muffle kiln (about 965°-1300°F or 500°-700°C). Sometimes, several firings are required to fuse the different colors of an elaborately enameled object.

The generic name for decorative windows made of pieces of colored glass fitted into cames and set in iron frames. Strictly speaking, the term is inaccurate because, in addition to glass colored by staining, glaziers used, and continue to use, glass colored throughout by metallic oxide, glass colored by flashing, and glass decorated with enamel.

Susceptible to being modeled or shaped. When it is in a molten state, glass can be described as plastic.

Its many meanings include an emblem impressed on wax or some other plastic substance as evidence of ownership or authenticity. Since the 17th century, many bottles have borne stamped glass seals that identify the producer of the contents, the tavern in which they were used, or the individual for whom the contents were bottled.

(1) In the hotshop, the reintroduction of a vessel into the glory hole to melt the surface and eliminate superficial irregularities; (2) in kiln working, exposing the object to significant heat so that it assumes a smooth surface.

A slight, narrow ridge on a glass object, which indicates that it has been made in a mold. The seams appear where gaps in the joins between parts of the mold have permitted molten glass to seep during formation. On well-made pieces, the seam marks are usually smoothed away by grinding or fire polishing.

Smoothing the surface of an object when it is cold by holding it against a rotating wheel fed with a fine abrasive such as pumice or cerium oxide. Glass can also be polished with hand-held tools.

The technique of removing the surface of an object with a rotating wheel fed with an abrasive, or by some other means.

A pocket of gas trapped in glass during manufacture. The term is used both for bubbles introduced intentionally (known as air traps or beads) and for unwanted bubbles created during the melting process. Very small bubbles are known as seeds.

A tool used to trim excess hot glass from an object in the course of production. Many modern shears are embedded with chips of industrial diamonds.

Any instrument used by glassworkers to develop and shape an object. Glassworkers’ tools include the blowpipe, pontil, gathering iron, jacks, shears, clapper, pallet, block, pincers, battledore, lipper, and crimper.

The result of chemical instability in glass caused by an imbalance in the ingredients of the batch, particularly an excess of alkali or a deficiency of stabilizer (usually lime). The instability of the glass results in an attack by atmospheric moisture, which produces a network of cracks in the surface that may feel damp or oily. Crizzling can be slowed or perhaps even halted, but it cannot at present be reversed. Crizzled glass is sometimes described as “sick” or “weeping.”

In glassmaking, a soluble salt consisting mainly of potassium carbonate or sodium carbonate. It is one of the essential ingredients of glass, generally accounting for about 15-20 percent of the batch. The alkali is a flux, which reduces the melting point of the major constituent of glass, silica.

Inflating a parison of hot glass in a mold. The glass is forced against the inner surfaces of the mold and assumes its shape, together with any decoration that it bears.

The technique of forming an object by inflating a gather or gob of molten glass on the end of a blowpipe. Traditionally and in modern furnace working, the gaffer blows through the tube, slightly inflating the gob, which is then manipulated into the required form by swinging it, rolling it on a marver, or shaping it with tools or in a mold. It is then inflated to the desired size. In flameworking, one end of the glass tube is heated and closed immediately, after which the worker blows into the other end and manipulates the hot glass.

The process of (1) heating the batch in order to fuse it into glass by exposing it to the required temperature in a crucible or pot, (2) reheating unfinished glassware while it is being worked, or (3) reheating glassware in a muffle to fuse enamel or gilding. The melting of the batch may require a temperature of about 2400°-2750°F (1300°-1500°C), whereas the muffle kiln may require a temperature of only about 950°- 1300°F (500°-700°C).

A type of 19th-century glassware with an allover silver appearance, made by applying a solution of silver nitrate between the walls of a double-walled vessel. The solution was introduced through a hole in the base, which was then sealed to prevent the silver from oxidizing. Silvered glass is sometimes known, mistakenly, as “mercury glass.” The technique was patented in England by Edward Varnish and F. H. Thompson in 1849, and in America by William Leighton in 1855.

(German, “gold between glass”) A type of decoration, produced in Bohemia and Austria in the 18th century, in which a design in gold or silver leaf is incorporated between two vessels that fit together precisely. Unlike Hellenistic and Roman gold glass, which is fused, Zwischengoldglas is bonded with cement.

Glass decorated with streaks of two or more colors, resembling marble. Marbled glass was a Venetian specialty from the 15th to 17th centuries, but it was also made in other times and places. Venetian marbled glass is known as calcedonio.

Glass that is colored by (1) impurities in the basic ingredients in the batch or (2) techniques of coloring glass by one of three main processes: (a) using a dissolved metallic oxide to impart a color throughout, (b) forming a dispersion of some substance in a colloidal state, and (c) suspending particles of pigments to form opaque colors.

Colored glass, often deep blue glass colored with cobalt oxide. Smalts are finely ground to use as colorants for glass and enamel.

A strand of glass, roughly circular in section, drawn out from a gather.

A metal rod with a spring clip that grips the foot of a vessel and so avoids the use of a pontil. Gadgets were first used in the late 18th century.

The pontil, or punty, is a solid metal rod that is usually tipped with a wad of hot glass, then applied to the base of a vessel to hold it during manufacture. It often leaves an irregular or ring-shaped scar on the base when removed. This is called the “pontil mark.”

A monochrome segment of glass cut from a trail.

Potassium carbonate. It is an alternative to soda as a source of alkali in the manufacture of glass.

A substance that lowers the melting temperature of another substance. For example, a flux is added to the batch in order to facilitate the fusing of the silica. Fluxes are also added to enamels in order to lower their fusion point to below that of the glass body to which they are to be applied. Potash and soda are fluxes.

An iron or steel tube, usually four to five feet long, for blowing glass. Blowpipes have a mouthpiece at one end and are usually fitted at the other end with a metal ring that helps to retain the gather.

Glass in which the flux is boric oxide instead of alkali. The first %%borosilicate glass%% was created by Otto Schott in 1882. It has a low coefficient of expansion and therefore withstands sudden changes of temperature.

A generic name for glass (e.g., borosilicate glass) with a relatively low coefficient of expansion. Soft glass (e.g., soda-lime glass), by contrast, has a relatively high coefficient of expansion.

(German, “pole glass”) A tall, narrow cylindrical drinking vessel (hence the name “pole glass”), usually with a pedestal foot.

A tall, narrow container for spoons. Spoon holders were used at the table from the mid-19th century to World War I.

The oxide of a metal. Oxides can be used to color glass and enamel, or to produce lustered or iridized surfaces. The resultant color depends primarily on the oxide used, but it can be affected by the composition of the glass itself and the presence or absence of oxygen in the furnace.

In glassworking, the process of coloring the surface of glass by the application of silver sulfide or silver chloride, which is then fired at a relatively low temperature. The silver imparts a yellow, brownish yellow, or ruby-colored stain, which can be painted, engraved, or etched.

A craftsman who paints and/or assembles glass windows.

The process of cutting into the surface of an annealed glass object either by holding it against a rotating copper wheel fed with an abrasive or by scratching it, usually with a diamond.

A drinking vessel with a bowl that rests on a stemmed foot.

(from Italian, “cup”) An ornamental dish or cup on a stemmed foot. Tazzas were generally made for drinking, for displaying fruit or sweetmeats, and as purely decorative objects.

The narrow part of a goblet or tazza that separates the bowl and the foot.

Nineteenth-century pressed glass whose patterns include extensive stippling to produce a bright, lacelike effect that conceals wrinkles caused when the cold plunger of the pressing machine came into contact with the hot glass.

(1) The technique of tapping the surface of a glass object with a pointed tool, often with a diamond or tungsten-carbide tip. Each tap produces a mark, and the decoration is composed of many hundreds or thousands of marks. (2) On lacy-pattern glass, the stippling is part of the decoration of the mold.

(1) The process whereby glass becomes partly crystallized as it cools (usually too slowly) from the molten state; (2) the crystals formed by this process. Devitrification can also occur on the surface as a result of unsuccessful annealing or accidental heating to a high temperature. It is not caused by chemical reaction between glass and its environment, which is known as weathering.

A substance, usually clay with a high silica content, capable of resisting high temperatures. Furnaces and pots are made from refractory materials.

Any crystalline inclusion present in glass. Stones consist of unmelted particles of batch, fragments of refractory material from the pot, or devitrification crystals. Stones of the first two varieties are generally irregular but rounded; those of the third variety are angular and well formed.

A fire-clay container in which batch is fused and kept molten. The glassworker gathers glass directly from the pot.

The process of slowly cooling a completed object in an auxiliary part of the glass furnace, or in a separate furnace. This is an integral part of glassmaking because if a hot glass object is allowed to cool too quickly, it will be highly strained by the time it reaches room temperature; indeed, it may break, either as it cools or at some later date. Highly strained glasses break easily if subjected to mechanical or thermal shock.

(from Latin strigilis, “scraper”) A scraper used by the ancient Romans to remove impurities from the skin after bathing. Although strigils were usually made of metal, a few glass examples are known to exist.

The fluid glass produced by melting batch.

An enclosed structure for the production and application of heat. In glassmaking, furnaces are used for melting the batch, maintaining pots of glass in a molten state, and reheating partly formed objects at the glory hole.

A drinking vessel in the form of an inverted cone. Cone beakers were used in several cultures, including ancient Rome, Sasanian Iran, and early medieval Europe.

A small ornamental object of white porcelainlike material, made to be encased in glass. The term is also applied to objects that are decorated with sulphides. They were popular in Europe and America throughout the 19th century. The term “sulphide” is probably connected with the use of sulfur by 18th- and 19th-century moldmakers.

A vessel for serving sweetmeats, sweet food such as preserved or candied fruit and sugared cakes or nuts.

A cylindrical or truncated conical one-piece mold with a patterned interior. The mold is open at the top so that a parison can be dipped into it and then inflated. It is also known as an optic mold.

A pattern of spiraling vertical ribs made by inflating the parison in a dip mold with vertical ribs, withdrawing it, and twisting it before continuing to inflate. The pattern is also described as wrythen.

(from French paraison) A gather, on the end of a blowpipe, that is already partly inflated.