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.

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.

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.

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

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.

A blob of glass applied to a glass object primarily as decoration, but also to afford a firm grip in the absence of a handle.

A defective object discarded during manufacture. Wasters are routinely recycled as cullet.

(1) Raw glass or pieces of broken glass from a cooled melt, intended for use as an ingredient of batch; (2) scrap glass intended for recycling.

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.

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.

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.”

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.

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 technique of decorating the surface of an object. Copper disks (wheels) of various sizes and rim profiles are rotated on a spindle. An abrasive such as Carborundum (in the past, emery was frequently used), mixed with oil, is applied to the edge of the wheel. The wheel presses the abrasive against the glass so that it removes the surface by grinding.

A process of decorating the surface of glass by the grinding action of a wheel, using disks of various sizes and materials (usually copper, but sometimes stone), and an abrasive in a grease or slurry applied to a wheel, as the engraver holds the object against the underside of the rotating wheel. See also Cutting and Copper-wheel engraving.

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.

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

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.

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.

The English term for an object made by a glassworker on his own time. Most friggers were made from the molten glass that remained in the pot at the end of the day. Such glass was considered to be a worker’s perquisite. American glassworkers referred to friggers as “end-of-day” objects. They are also known as whimsies.

The English term for an object made by a glassworker on his own time. Most friggers were made from the molten glass that remained in the pot at the end of the day. Such glass was considered to be a worker’s perquisite. American glassworkers referred to friggers as “end-of-day” objects. They are also known as whimsies.

The English term for an object made by a glassworker on his own time. Most friggers were made from the molten glass that remained in the pot at the end of the day. Such glass was considered to be a worker’s perquisite. American glassworkers referred to friggers as “end-of-day” objects. They are also known as whimsies.

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

A late 17th- and 18th-century English drinking vessel engraved with a toast, a symbol (an orange tree, for example), or a motto supporting William of Orange (King William III, r. 1689-1702), or with his portrait. William III was a Protestant, and his political opponents were the Roman Catholic Jacobites. Many Williamite glasses have been shown to be late 19th century fakes, some perhaps executed by the Bohemian glass engraver Franz Tieze (1842-1932).

A decorative bottle with a stopper, used for serving wines and spirits.

A type of goblet with the stem in the form of vertical, winglike flanges composed of trails arranged in a complex design that may include dragons, sea horses, and other creatures. The German term for a winged goblet is Flügelglas.

A type of goblet with the stem in the form of vertical, winglike flanges composed of trails arranged in a complex design that may include dragons, sea horses, and other creatures. The German term for a winged goblet is Flügelglas.

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

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

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

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.

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.