Corning Museum of Glass

Glass made in the rural glasshouses of central and northern Europe in the late Middle Ages and the early modern period. Most forest glass was fluxed with potash derived from the wood with which the furnaces were fueled. It is green because of iron impurities in the sand from which it was made. The German term for forest glass is Waldglas.

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.

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

(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.

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.

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.

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.

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.

(Noun) A mass of molten glass (sometimes called a gob) collected on the end of a blowpipe, pontil, or gathering iron; (verb) to collect molten glass on the end of a tool.

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.

The technique of decorating glass by scratching the surface with a diamond. Diamond-tipped tools may have been used by the ancient Romans and in the medieval Islamic world, but they were popularized by the Venetians in the 16th century. Diamond-point engraving was carried to some of its greatest artistic heights in the Netherlands during the 17th century. Today, other hard materials, such as tungsten carbide, are used instead of diamonds.

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.

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.

A technique adapted from metalworking. The object to be fashioned in glass is modeled in wax and encased in clay or plaster that is heated. The wax melts and is released through vents or “gates,” also made of wax, which have been attached to the object before heating. The clay or plaster dries and becomes rigid. This then serves as a mold, into which molten or powdered glass is introduced through the gates. If powdered glass is used, the mold is heated in order to fuse the contents. After annealing, the mold is removed from the object, which is then finished by grinding, fire polishing, or acid etching.

Work that is perforated. Openwork in glass objects can be made by creating a network of trails, by casting (see Diatreta), or by cutting (see Cage cup).

The generic name for a wide variety of techniques used to form glass in a mold.

An ancient Roman vessel decorated by undercutting so that the surface decoration stands free of the body of the glass, supported by struts. The vessel appears, therefore, to be enclosed in an openwork cage. Cage cups are sometimes known as diatreta or vasa diatreta.

vas diatretum (Latin, “openwork vessel”) A term frequently used to refer to a cage cup. The plural form is vasa diatreta.

A term used by Frederick Carder (1863-1963) to describe openwork objects that he made by lost wax casting.

An ancient Roman vessel decorated by undercutting so that the surface decoration stands free of the body of the glass, supported by struts. The vessel appears, therefore, to be enclosed in an openwork cage. Cage cups are sometimes known as diatreta or vasa diatreta.

A mold made of two or more parts.

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.

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

Glassware formed by placing a blob of molten glass in a metal mold and pressing it with a metal plunger or “follower” to form the inside shape. The resultant piece, termed “mold-pressed,” has an interior form independent of the exterior, in contrast to mold-blown glass, whose interior corresponds to the outer form. The process of pressing glass was first mechanized in the United States between 1820 and 1830.

A stand with a socket or spike for one candle.

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

(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.

(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.

The term applied to several types of Hellenistic and ancient Roman glass objects decorated with designs cut and/or engraved in gold leaf, which is sandwiched between two fused layers of glass. Hellenistic gold glass was made by sandwiching the decoration between two closely fitting cast, ground, and polished vessels, which were then fused. Many Roman gold glasses apparently were made by applying the gold leaf to the surface of an object, reheating it, and inflating a parison against the decorated surface.

A type of goblet with the stem in the form of a dragon with a convoluted body, outspread wings, open jaws, and a crest. Known in Italian as vetri a serpenti (serpent glasses), dragon-stem goblets were first made in Venice in the 17th century. They were imitated in the Netherlands by producers of façon de Venise glass.

(French, “manner, or style, of Venice”) Glass made in imitation of Venetian products, at centers other than Venice itself. Façon de Venise glass was popular in many parts of Europe in the 16th and 17th centuries.

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

The process of pulling semimolten glass to elongate it. It is used, for example, in the production of canes.

The process of using a rotating drill to make a hole.

The reservoir for oil in a lamp.

A small container consisting of a blown glass flask adorned with trails that may form an openwork “cage” and fused to the back of a camel-like animal, made by manipulating hot glass. Dromedary flasks were made in Syria between about the sixth and eighth centuries A.D.

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

The part of a lamp where the flame is produced.