Corning Museum of Glass

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 tool shaped like a pair of pliers, with flat jaws containing molds. Hand presses were used extensively in Europe for making chandelier parts. Later, they were introduced in the United States for pressing stoppers and bases.

(from French, “candlestick”) A lighting fixture suspended from the ceiling, with two or more arms bearing lights (originally, candles) or two or more pendent lights. Many chandeliers have faceted lead glass arms, candle cups, shafts, and prisms, which reflect the light and sparkle like tiny mirrors.

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 Some molds (e.g., dip molds) impart a pattern to the parison, which is then withdrawn, and blown and tooled to the desired shape and size; other molds (sometimes known as full-size molds) are used to give the object its final form, with or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.

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.

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.

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 generic name for glass (e.g., soda-lime glass) with a relatively high coefficient of expansion. The term hard glass (e.g., borosilicate glass) refers to glass with a relatively low coefficient of expansion.

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.

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.

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.

A mold-blown flask with the body in the form of a human head. Head flasks were popular in the Roman Empire, and examples were made from the first to fourth centuries A.D. Vessels decorated with two faces placed back to back are sometimes known as “janiform” head flasks (from Janus, the spirit of doorways, who was represented as a double-faced head).

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.

A type of borosilicate glass perfected in 1915 by W. C. Taylor and Eugene Sullivan of Corning Glass Works in Corning, New York. Pyrex rods can be used in flameworking.

A type of translucent yellow-shading-to-pink Art Glass made by the Mt. Washington Glass Company in New Bedford, Massachusetts, between 1885 and about 1895.

A very rare type of thick-walled glass beaker with relief-cut decoration of lions, griffins, eagles, and other motifs. Hedwig beakers date from about the 12th century, but their place of manufacture is unknown. They are so called because one of the surviving examples is said to have belonged to Saint Hedwig of Silesia (d. 1243).

A type of cut glass with decoration in high relief, made by removing the background.

The technique whereby glass is removed from the surface of an object by grinding it with rotating wheels made of stone, wood, and cork. The first stage of the process employs a stone wheel under a continuous stream of water. Later, wheels of fine-grained stone and wood, fed with various abrasives, are used to grind and polish the surface.

A highly corrosive acid that attacks silicates such as glass. Pure hydrofluoric acid dissolves glass, leaving a brilliant, acid-polished surface.

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.