Glossary of Glass Terms

Acid Etching This process for the decoration of glass involves the application of hydrofluoric acid to the glass surface. Hydrofluoric acid or a similar chemical may be used to give glass a matte, frosted appearance (similar to that obtained by surface sandblasting). Glass designs can be produced by covering the glass with stencil material and then cutting the desired pattern through the stencil layer. When applied, the acid will corrode the glass but not affect the covered areas.

Ancient Glass Generally refers to glass made before the Venetian era of glassmaking.

Anneal To cool glass by reintroducing a completed object into an auxiliary part of the glass furnace and slowly cooling the object so that any strain created in the glass during the forming process may be released. The critical area for cooling is 1000-800 degrees Fahrenheit. Under natural conditions, the surface of molten glass will cool more rapidly than the center. This results in internal stresses that may cause the glass sheet or object to crack, shatter, or even explode at a later time. The annealing process is designed to eliminate or limit such stresses by submitting the glass to strictly controlled cooling in a special oven known as a "lehr." Inside the lehr, the glass is allowed to cool to a temperature known as the "annealing point." When the glass reaches this point, the lehr temperature is stabilized for a specific length of time (depending on the glass type, its thickness, its coefficient of expansion, and the amount of residual stress required) to allow stresses present in the glass to relax. This phase is followed by a period of cooling with a predefined temperature gradient.

Antique glass A trade term for glass more than twenty-five years old.

Blown glass The shaping of glass by blowing air through a hollow rod into the center of a molten glass gather.

Cane Any string or rod of glass.

Cold shop A glassworking studio that does not have a furnace or glory hole.

Cut glass Glass that is decorated by using grinding stones that are worked wet to cut designs onto the glass.

Direct carving Glass chunks that are carved, ground, chiseled or otherwise shaped like other sculpture materials.

Enameled glass Opaque glass colors, which are actually glass powders, that are melted onto a glass surface.

Engraving Design that is cut into or scratched onto glass with a diamond point, stone, metal, or copper wheel. Usually more complex and flexible than cut glasswork.

Etching Adding designs to glass by etching with hydroflouric acid or similar product.

Fire polish The reintroduction of an object into the furnace in order to smooth an irregularity. A technique used to retain a shiny surface to glass after it has been ground on a grinder or sandblasted.

Flashing Very thin layer of colored glass fired or vaporized on base glass often of another color.

Gather A ball of molten glass taken from a pot or furnace on the end of a hollow blow rod.

Gilded or Guilding Firing metals such as gold onto glass.

Glory Hole A high-temperature chamber used for reshaping glass either on a punty rod or blowpipe.

Hot shop A glassworking studio containing a furnace and glory hole, sometimes referred to as a glassblowing studio.

Incalmo Joining two or more blown sections while hot.

Iridescence Thin laminated flakes of glass showing decomposition with age. Technique perfected by Tiffany.

Iridized glass Glass with a surface that is chemically treated to have a rainbow or iridescent appearance.

Kiln Insulated chamber for heating and cooling glass or ceramics.

Kiln-formed Glass that is altered, fused, shaped, slumped, or textured by the heat of a kiln.

Latticino Threads of white or colored glass within clear glass, sometimes lacelike in pattern.

Lampwork Any glassworking technique done with the direct flame of a torch; glasswork done with preformed glass rods and tubes.

Leaded glass Stained glass window held in place by lead came.

Lost wax casting Modeling an object in wax and cased it in a ceramic or plaster mold. The mold is heated and the wax flows out, after which powdered or molten glass is poured into the mold.

Millefiori The Italian term, which means "a thousand flowers," used to describe mosaic glass objects created using slices of glass canes.

Mosaic Glass vessels or objects built up of preformed elements of glass placed around or in a mold and slowly heated until the glasses fuse together.

Overlay Blowing a bubble with color on the inside, the bottom is attached to a solid core and then the bubble is turned inside out, leaving a thin color "flash" on the outside.

Punty rod A solid metal rod used to transfer and hold glass when working with a glory hole.

Sandblasting Creating designs on the surface of glass by using high-pressure air mixed with sand applied to the surface of glass to carve texture.

Slump A technique used to form glass using a mold, heat, and gravity.

Thermal Shock Glass breakage caused by rapid or uneven heating or cooling.