The Hot Shop Glossary was compiled by docents under the guidance of the Hot Shop team of artists and is available in the Docent Room files as a part of the docent training curriculum. Go ahead an quiz yourself. Could you explain these terms to a visitor?

Annealer: an oven, made of high temperature insulating ceramics that is used for cooling the glass at a controlled rate. A piece of glass that has just come off of the pipe has many different temperatures throughout the piece. These different temperatures cause stress which in turn can crack the glass. Annealing homogenizes the temperature of the glass thus relieving the stress and then slowly brings the glass down to room temp over a period of time. How long a piece stays in the annealer is directly related to how thick it is. The average annealing cycle is 8-12 hours for blown work. A thick paperweight may stay in for 2 days. The Hubble telescope lens was annealed for three years.

Avolio: hourglass shaped connecting piece commonly seen in venetian style goblets. The avolio serves as not only a visual element, but also provides a thin spot which makes it easier to use the fork to load the goblet into the annealer.

Batch: term used to describe the glass in its raw state. The museum’s glass is a soda-lime glass (beer bottles, windows), as opposed to a borosilicate glass (pyrex). The main three ingredients in a soda-lime glass are silica, soda ash and lime. Silica melts at about 3000%, soda ash is added as flux to allow the sand to melt at a lower temperature and lime is used to stabilize the silica and soda ash mixture. The museum’s batch is brought from the Philips Co. in Holland. The sand comes from Belgium, pure sand is important to good glass making.

Cased : glass object covered with a layer of colorless glass or with glass of a different color. Sometimes this is referred to as flashing.

Cathedral Glass: Glass sheets for manufacturing leaded glass windows and mosaics. Louis Comfort Tiffany maintained at least one cathedral glass shop in his glass-works, in which a dazzling variety of colors, textures and degrees of translucency was developed. In 1897 Cecilia Waern reported in The Studio that Tiffany maintained an available stock of 200 to 300.

Cire Perdue: The French term for Lost Wax. This is a process in which a model is carved in wax then has a mold built up around it. When this is heated, the wax melts and runs out through small holes in the base of the mold, which is thus left with the exact contours of the original wax model. The mold can them be filled with molten glass or bronze which, on cooling, appears as an exact replica of its original model. Some molds are re-usable, others are destroyed when opened.

Cold Work: Finishing work after the piece is annealed. It may involve grinding , cutting, sandblasting, etching, polishing, and engraving to manipulate glass in its cold, solid state. Typical tools include: Flat Grinding Wheel—machine consisting of a large flat spinning wheel used to flatten the base of glass pieces; Pumice and Cerium Wheels—the two final polishing stages invove felt lined wheels used in conjunction with a pumice and cerium oxide slurry to bring the glass to a smooth polish; Lathe (Punty Grinder)—used to grind away the Punty Mark or remove excess material; and Diamond-blade Chop Saw—Large chop saw armed with a water-fed diamond tipped circular blade used to cut glass.

Color Bars: Bars of concentrated colored glass about 1” in diameter and a foot long. The glassblower cuts these in smaller chunks to melt, crush or overlay the softened bar over a bubble. MoG purchases color bars from Kuegler (Germany) and Gaffer (New Zealand). The glass is colored with different metal oxides, which are the same elements used to pigment paint. Cobalt makes blue, iron for green and sometimes brown, selenium for yellow, cadmium for red. Gold is also used for certain shades of red.

Color Oven: any small kiln (or corner of the annealer) used for preheating chunks of color bars to about 1000˚ F to allow pickup without cracking. There is usually a blackboard near the Color Oven to plot the layout of the various colors it contains.

Crystal: glass with 20 – 30% lead oxide added is called crystal. This makes a soft, clear glass that reflects and refracts light brilliantly, making cut crystal sparkle. It is a softer glass than soda-lime glass.

Enamel: 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 kiln.

Engraving: the process of cutting into the surface of the glass using rotating copper wheels of varying sized coated with an abrasive powder in oil. Relief engraving produces a raised decoration (cameo).

Etching: a surface treatment using hydrofluoric acid. Different effects art possible depending on the concentration and temperature of the acid and additives. Needle etching is used for signatures or interior details.

Factory Glass: Stueben, Blenko and Fenton are examples of factory glass in the U.S. In the 19th century, all glass was made in factories, a team of workers producing the same piece repeatedly.

Favrile: the Trade Mark registered by Louis Comfort Tiffany in 1894 referring not only to the iridescent glass he manufactured, but also to his other creations, including ceramics, lamps and leaded glass windows. It is derived from “febrile”, an Old English work indicating the product of a craftsman.

Flamework, Lampwork: a process which involves using a torch to heat rods of tubes of glass that will be manipulated into different shapes. Welding parts together is the most complicated form of artistic glass design using this technique. It creates efects that are not possible at the furnice.

Float Glass the process for making modern high quality window glass by floating molten glass on a bath of molten tin (under nitrogen to keep frim oxidizing the tin) and pulling a continuous sheet of flat glass off the other end. Before float glass, plate glass was cast and ground and polished and window glass was made by hand either by spinning roundels or by blowing cylinders (then flattened) from which panes/ lights were cut.

Frit: is made by crushing up large chunks of colored glass. The frit is sorted by size, starting at zero and going to four. Zero being like fine grains of sand, and for being the size of small pebbles. Again, this is bought from the same manufacturer as the color bar. Creates a spotted or modeled look.

Furnace: a container built of several types of high temperature insulating ceramics that is used to melt and hold glass at high temperatures (working temp: 2125 degrees, melting temp: 2300 degrees). The glass is corrosive and will break down the interior liner of the tank over a period of time. There are many different furnace designs, with the average life of a furnace being 5 to 8 years. The furnace is fired with natural gas.

Glass-painting colors: subdivided into cold and firing colors. Cold painting entails applying the paint (watercolor, tempera, oil, lacquer paints, etc.) and letting it dry, which is not very durable. Colors for firing are subdivided into four groups: 1) enamel (opaque enamel, transparent enamel and flat colors); 2) precious metals (bright or gilt painting, silver or platinum); 3) Stain 4) Luster pigments. Firing colors are applied, dried and then fired in a muffle kiln at temperatures between 965˚ F to 1300˚ F. They are of highly variable durability, depending on how they bond with the surface of the glass. Stain is the most durable form, and luster is the least durable form.

Glory Hole: a round chamber made of high temperature (working temp: 2200 degrees) insulating ceramics used for reheating the glass. Glass must be kept at a working temperature of 1200 – 2000 F until the piece is finished. Glory holes often have two or three sets of doors that can be opened and closed to accommodate the size of the piece being made.

High Fire Enamel Paint and Decals : a decal is a water slide transfer of a printed image that is fused onto glass or ceramics. High fire enamels – such as Paradise prints, initially created for coating steel and modified for hot glass techniques – are screen printed onto a decal. The enamel melts onto the blown object rather than burning off at high temperatures.

Hot Shop: a workshop where molten glass is blown, cast or manipulated.

Incalmo: a technique that usually results in two distinct sections of color in a vase-like object. It is done by opening out two blown pieces so the lips are identical in diameter, heating and bringing the edges together. The joined piece is then freed from one pipe/punty and further worked. Most commonly a bowl is created and puntied for one piece while the other is still on the pipe and is opened for joining without having to be freed from the pipe. When it is freed, the opening at the pipe becomes the mouth of the piece.

Irridescent Glass : a shimmering layer on the surface of the glass created by vaporizing glass in a glory hole with mixtures of metallic compounds (zinc, chloride, arsenic, barium, strontium, nitrate). It can also be created with a de-vitrifying agent applied to change the properties of the surface glass, causing light to reflect and bend.

Kevlar Mitts: are used when loading work into the annealer. The assistant typically wears the mitts, preheats them with heat from the glory hole or furnace. Then the piece is broken off the end of the punty into the mitts and loaded into the annealer.

Light Screens—Frank Lloyd Wright : from 1885 – 1923, Wright designed more than 4500 windows for 160 buildings. He used predominantly clear glass and abstract geometric shapes to create transparent glass screens between inside and outside environments. He used the term “light screens” to describe the shoji screen effect.

Lustered glass: finishes achieved by mixing one or more metal resonates (gold, silver, platinum, copper, lead, iron) with volatile olds (lavender, rosemary, peppermint) and brushed onto the surface. It is then dried and fired at 550 – 600 degrees. It can be colorless or colored, and has limited durability because of it cannot bong with the surface of the glass.

Marver: is a metal table used to shape, chill and center the piece. Marvering at different angles is a tricky but necessary skill for glassblowers to master.

Opalescent Glass : semi-opaque, with a milky appearance. It can be one solid color but generally is a mixture of two or more colors with streaks and swirls.

Overlay: an overlay is a way of using the color bar. After being preheated in the color box to around 1000 degrees, the bar is then picked up on a punty rod. It is then heated in the glory hole until it is in a molten state. While this is happening, a small clear bubble will be blown and cooled on a separate pipe. When the color is hot enough, it is cut off onto the end of the clear bubble, and smoothed over the clear glass, creating an overlay of color. An overlay creates an even layer of color sandwiched between two or more layers of clear glass.

Pipe Warmer : a small box made of high temperature insulating ceramics and a burner that is used to heat the end of a blowpipe or punty. Hot glass will not stick to cold metal.

Powder: is similar to frit, yet even finer. It is comparable to flour. Powder is created by further crushing the colored glass into powder. This form of color is especially hazardous to work with, because of its ability to become air born. It is usually sifted onto the surface of the glass in a powder booth.

Punty: most often a solid tipped rod, with a hollow or solid shaft. The vessel on the blowpipe is transferred to the punty so the lip/mouth of the glass can be worked. Also, used for gathering glass for hot bits of various shapes. Usually 54” long like blowpipes, ½” tip is the most common.

Rolling Yoke: is a necessity when making larger scale or heavier pieces. The gaffer can move the yoke towards the glory hole as needed to help manage the weight of the piece

Rondel: a mouth-blown piece of glass that has been spun into a circular shape, often irregular. They were sometimes incorporated into leaded glass artworks. Machine-made facsimiles are called “pressed rondels”.

Sofietta: a hollow tube with a cone on the end used to blow up the glass vessel while it is on the punty.

Stained Glass: term used to describe any colored flat glass or any object made of such glass joined by metal strips. Originally, colored or clear flat glass cut to fit an artist’s design on which details were painted in pigment with a brush. The glass pieces were then heated in a kiln or oven to bond the pigment ot the glass surface. Most religiouos windows from medieval times to the 20th century were made in this way.

Tazza: the tazza is one of the hardest shapes to make well. It is a low bowl form and is used for champagne or possibly desert. It is extremely difficult to get smoothly contoured sides.

Tweezers: are made long for glass working, widespread and have bent in tips used for grabbing, picking and opening up the end of bubbles.