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 Term used to describe art glass produced by the mouth-blown cylinder which is first blown, then annealed and colled. The cylinder is then scored lengthwise, separated and re-heated and shaped into a flat sheet. The finished sheet is premier art glass with linear striations and a very smooth surface and often is one-of-a-kind in appearance.
- Baroque™ A machine made "reamy" glass, created by combining glasses of mis-matched compositions. The different glasses "oppose" each other when they are stirred together, creating artistic 3-D swirls. A Spectrum Glass Company trademarked glass.
- Bent (or Slumped) Glass Glass which has been heated in a kiln from room temperature to a temperature high enough to cause it to soften and slump (sag) into or over a mold. The finished item takes the shape of the mold.
- Bevel Cold glass (usually clear, thick plate) with edges that have been ground and polished to an angle other than 90 degrees. Transmitted light is refracted and a prism-like effect results. Bevels are available in a variety of sizes, shapes and geometric configurations (called "clusters") for incorporation into leaded glass work.
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.
COE Coefficient of Expansion The ratio of the change in length or volume of a glass to its original length or volume per unit change in temperature. Used to help determine compatibility of different glasses for the fusing process.
Cold shop A glassworking studio that does not have a furnace or glory hole.
Combing A process in which a rake-like tool is drawn across molten glass and the results are artistic patterns in the glass.
- Compatible Glasses are said to be compatible if, after being fused together by blowing or kiln forming and properly annealed, they remain relatively free from internal stress.
- Copper Foil Thin, narrow strips of adhesive-backed copper tape used to wrap the edges of glass pieces that have been cut to fit a pattern. Once wrapped, solder is applied, bonding the glass pieces together. Assembling a stained glass project in this manner is called the "copper foil technique."
Cut glass Glass that is decorated by using grinding stones that are worked wet to cut designs onto the glass.
Dalles Thick slabs of cathedral glass approximately 1" in thickness
- Dalle de Verre An art glass medium in which dalles are broken into pieces with a hammer and set in an epoxy base to adhere them in a decorative design. Dependent on large scale for best appearance, they are primarily used in church architectural applications and are recommended due to their security.
- Dichroic A glass that has been coated with one or more ultra-thin layers of transparent metal oxides designed to enhance reflections at specific wavelengths of light. The process occurs in a vacuum chamber at elevated temperatures. The resulting effects are striking and brilliant color reflections which often change at varying angles.
Direct carving Glass chunks that are carved, ground, chiseled or otherwise shaped like other sculpture materials.
Drapery Glass Glass sheets with multiple folds and used for petals and scultpured objects.
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.
Flashed Glass of one color with a very thin layer of another color on one side. Flashed glass is often used for etched or sandblasted glass art. When sections of the thin color layer are removed, the base color shows through.
- Flux Chemical agent (liquid or paste) used to facilitate the flow of solder and prevent formation of oxides during soldering.
- Frit Ground glass, ranging in a variety of sizes from fine powder to gravel-like size. Frit is sometimes used for painterly effects and can be fused or cast.
- Fused Glass Glass that has been fired in a kiln at a temperature high enough to melt different peices together.
- 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.
Glue-Chip A texture created on the surface of cold glass by applying hot animal glue and allowing it to dry under controlled conditions. As the glue dries and contracts, it chips the glass surface in a natural and attractive pattern, likened to frost on a window pane.
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 Surface treatment in which a layer of metallic oxide is bonded to the hot glass surface just after sheet-forming, resulting in a colorful, shimmering effect.
Jewel A piece of glass that has been cut and faceted or press-molded into a geometric shape. Jewels are often incorporated into leaded glass artwork.
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 Glass pieces joined with metal strips (lead came). Solder is applied to the joints of the came to hold the pieces together.
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 A design or picture made by setting small colored pieces of glass or ceramic material into a surface using cement or grout as a bonding agent.
Murrini A thin slice of pre-worked glass cane that can be used as a component in another glass object.
- Nugget A small, irregularly shaped "glob" of glass, flat on the bottom, rounded across the top. Nuggets can be foiled or incorporated into leaded glass artwork.
- Opalescent Glass that has opacity depending upon the composition and temperatures used in the manufacturing process.
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.
Painted Glass Glass on which special paints (containing fine frit) have been applied and then heated in a kiln to a temperature high enough to fuse the pigments permanently to the glass surface. Referred to in medieval times as "stained glass."
- Pate de Verre Glass frits spread in a decorative design sometimes in a mold, then fired in a kiln.
Punty rod A solid metal rod used to transfer and hold glass when working with a glory hole.
Ripple A surface texture of glass that has irregular ripples.
- Rods Cylindrical, pencil-thick sticks of glass used primarily in flameworking and glass bead making. They are available in a wide color range and many expansion coefficients.
- Rondel A mouth-blown piece of glass with a circular shape. These are incorporated into art glass and leaded glass artworks. Machine-made facsimiles are common, called "pressed rondels."
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.
Seedy Glass Glass in which air bubbles are entrapped and visible.
Slump A technique used to form glass using a mold, heat, and gravity.
Solder Alloy, usually tin and lead, used to join metallic parts, or the term used as the act of applying metals in both the leaded and copper foil techniques of stained glass work.
- Stained Glass Colored flat glass or any object made of such glass joined by lead came or coppper foil. Once the medieval term for painted glass, it is now used as a general term to define the art, the craft, and the industry.
- Streaky Glass Two or more cathedral glasses mixed together to create a multi-colored glass sheet. Some use this term also to describe Mixed Opalescent glass as defined above.
- Stringer A spaghetti-like glass shape used as a decorative element in the hot glass arts.
- Tested Compatible Descriptive of glasses which have been tested and identified as compatibility with each other when combined in a hot glass process like blowing, fusing, or casting.
- Thermal Shock Glass breakage caused by rapid or uneven heating or cooling.
- Wispy Mixed opalescent glass with only thin wisps of white, like lazy cloud trails.