Glossary of Materials & Terms Used in Furnace Glassblowing

Rev. 2002-12-26, 2003-01-26, 02-05, 02-16
2004-03-08, -12-07, 2006-06-29, -10-03, 2009-02-25, -07-26, -09-24, 2011-07-23

A listing of materials used in making glass, building equipment, etc. for furnace glassblowing and notes on where to get them. Added: [2005] Alumna, Boric, [2006] Paper, Acid, Graphite 2009 Slag, Oxygen 2011 Glass Clay

For a remarkable online list of definitions of materials CI Materials Handbook with lots of details.  Search All Materials for the full, long, list or select a name from the list.

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A
Acetylene
A pure gas compound (HC2H) mostly made by man and supplied in tanks for use as fuel for a very high temperature (4000F) flame for welding and metal cutting. Dangerous in that it is explosive over a wide range of air/gas mixtures. 2009-07-26
Acid
Chemicals which have H in their designation.  Not a lot of use in glass work.  Weak acids are used for cleaning glass, most commonly vinegar containing citric acid. Strong acids include Hydrochloric (HCl), Sulfuric (H2SO4), Nitric (HNO3) and Hydrofluoric (HFl)  Hydrochloric acid is sold as pool shock in grocery stores.  Sulfuric acid is sold to charge car batteries and is used to clean metals..  Both are very strong and must be handled with care, damaging clothes and concrete.  Nitric acid is harder to get.  Hydrofluoric acid is incredibly dangerous because it penetrates the skin without pain and destroys the bone underneath. Fluorine gas given off in reactions is also dangerous.  It is one of the few acids that will dissolve glass and thus has been used to selectively remove parts of designs not protected by wax or asphalt. Requires great care and good ventilation for proper use. 2006-10-03.
Air
Air is a material for glass BLOWING, amazingly enough, but it is also used for cooling pieces as well as being supplied under pressure to burners and moved for ventilation. Burners  Ventilation
Alumina, aluminum oxide (Al2O3 )
"Makes glass stronger and blunts attack by acids and alkalis and increases elasticity of glass." AmGlPrac 2005-02-09
Antimony oxide (Sb2O3)
An ingredient in glass making when mixing batch. Further information at batch.htm
Asbestos
A fibrous mineral previously mined and much used for heat and electrical insulation. Unfortunately, it breaks down and produces long, thin, essentially invisible fibers that when breathed are taken into the lungs and encased with flesh, making them non-removable while they reduce the capacity of the lungs (asbestosis.) Ceramic fiber blanket is an alternative but reportedly has some of the same problems, especially once heated.
B
Barium carbonate (BaCO3)
An ingredient in glass making when mixing batch. Further information at batch.htm
Batch
Glass can melted from broken glass cullet or be made from a mixture of chemicals, mostly sand. Batch can be mixed by the worker or bought. Most commonly used bought batch is from Spruce Pine Batch Co. although several other companies have started offering batch.. Mixing batch requires care as many ingredients are poisonous or lung damaging. Sand, Lime, Limestone (Calcium Carbonate), Soda (Sodium Carbonate), Soda Ash, Potash (Potassium Carbonate), Lithium carbonate, Feldspar, Sodium nitrate, Zinc oxide, Barium carbonate, Fluorspar, Antimony oxide, Arsenic.  Further information at batch.htm
Bead Board
The white fluffy firm plastic insulation often called Styrofoam.  Bead board is made by steam heating hard little beads in a mold where they fluff up and bond together. Much easier to find.  Styrofoam is filled with bubbles and harder and is made with a chemical mixture.  Mostly used like lost wax in casting.
Bee's Wax Beeswax
Used to lubricate jacks and other tools. From fabric stores or use a candle. Carnauba wax is harder. Wax mixtures, especially on older steel (vs. stainless steel) jacks are a heartfelt topic among gaffers.
Blocks
Blocks are chunks of fruitwood, most commonly cherry but also pear and apple, which are carved to a shape useful in forming glass and then soaked in water until waterlogged. The steam from the water and the carbon that forms on the surface makes a durable tool. Usually will crack if allowed to dry out. Wooden rods and paddles are also used the same way. Walter Evans makes blocks for many studios. Blocks, Paper & Wood
Boric Acid, Borax (H3BO3, Na2B4O7 + 10H2O)
Ingredient in making glass.  Especially important in making borosilicate low expansion glasses such as Pyrex which withstand heat shock.  Makes glass stiffer to work.  2005-02-09
C
Castable
Shorthand name for high temperature refractory materials that are in powder form, mixed with water and poured in a mold for forming, as opposed to rammable, brick, and block. Materials may result in the equivalent of an insulating fire brick or solid high temp fire brick. Used for building high temp equipment.  Refracto.htm
Ceramic fiber blanket, board & paper
Modern industrial high temperature insulation to replace much more dangerous asbestos. Available in several forms and several temperature ranges. Refracto.htm
Cold Working
The general name for sandblasting, grinding and polishing the glass. While many artists use the procedures of cold working as part of their artistic creation, most would prefer to avoid the labor intensive process of grinding off punty marks and polishing the result.
Colloidal silica
used as a rigidizer for frax and for making molds. "micro-fine particles of silicon dioxide(SiO2 ) dispersed in water. 30%-40% SiO2 is common. If the particles are smaller than about 7nm [0.000000007m 0.00000027"] the sol is almost as clear as water. From 10 to 30nm there is a characteristic opalescence or translucency when seen it, and above about 50nm the appearance is white and milky." colloidal silica site
Color bars
Glassblowers using moderate amounts of color in their glass buy bars of concentrated colored glass about 1" in diameter and a foot long. This is cut in smaller chunks and melted, crushed or pulled. Sold by the kilo for a full bar, cost is effectively $1-3 per inch ($17-48 per kilo.) Those using more color tend to melt their own to reduce cost. Color
Crystal
When being precise by modern definition, glass with approximately 20-35% lead oxide added.  This makes a soft clear glass that reflects and refracts light brilliantly, making cut crystal sparkle.  The glass also, when thin, has a distinctive bell-like ring when gently struck and will "sing", as in a glass harmonica when rubbed on the rim with a wet finger.  Less precisely, any clear uncolored glass that resembles rock crystal (clear quartz, the original crystal balls) so fine clear glassware is referred to as crystal and the original crystallo (sp) from Murano Italy was made with very pure (no iron) flint but had no lead which was added in England.
Cullet
Broken glass, which melts with less energy than batch. Can be remains of previous work, bottle or window glass, or purchased. The latter two may need chemical additions to make more workable. Available from Gabbert Cullet from pressed glass factory operations and in both cutoffs and custom pellets from Spectrum's stained glass operations.  Slag
D
E
Enamel

Glass color ground up and mixed with other chemicals to lower the melting point to apply to metal or glass surfaces to melt it onto the surface without melting the glass below.  Frit is just ground glass, melting at the same point.

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F
Feldspar
An ingredient in glass making when mixing batch. "a silicate of alumina and either potash or soda (or both)", so is a natural glass of a not exact formula, roughly 65% silica, 20% alumina, 10% soda or 12% potash. Further information at batch.htm
Fire brick
A brick made to withstand high temperatures, costing more the higher the temperature, from $1.50 to $20 a brick. Usually very hard and heavy, a poor insulator. Available in many shapes. Used for furnaces mostly. See also Fire brick, Insulating. From A.P.Green, Mexico MO and local offices, National Refractory, see Refractory in Yellow Pages..
Fire brick, Insulating
A very light, soft, easily cut, high temperature material than can form structural walls and backup hard fire brick.
Fluorspar (CaF)
An ingredient in glass making when mixing batch. Further information at batch.htm
Frit
Chunks of broken glass the size of raisins to grape nuts, bigger than powder. Can be bought, for smaller quantities, usually made with crusher if color bar is on hand.
Fuel
Glass melting takes a lot of fuel, most often propane and natural gas in modern studios, and natural gas in factories, but originally wood until it came into short supply then coal which requires special covered pots.
G
Gather
Both the name for going to the furnace to get glass (to gather, gathering) and for the glass gotten (first gather, second gather). The end of the pipe or punty is lowered into the glass and turned to drag the glass evenly around the pipe or previous gather. The analogy most often used for the process is turning a spoon or old fashioned wooden pickup in honey, keeping it turning to get to the plate. However, gathering glass involves stuff that is over 2000F that will melt and deform the previous gather if done too slowly (not to mention set clothes smoking.)
Glass
Well, golly gee whilikers, really? Glass. A material used in glassblowing?  Well yes.  Common glass is made from sand, limestone, and soda ash with other chemicals to make it easier to melt, remove bubbles, de-color it to clear or give it color, and so forth.  Common window, bottle, and glassware glass is soda-lime.  If borax is substituted for the soda-lime the result is borosilicate, sold as Pyrex, which melts at a higher temperature, expands and contracts less, and is less likely to break with abrupt temperature changes, so it is used with cookware, scientific lab ware and telescope lenses.  There are many specialty glasses for optical clarity, toughness, unique light transmission, and so forth. Batch, Cullet, Crystal
Glass Clay
Glass clay is a relatively new product that performs somewhat like pate de verre and precious metal clay while allowing making of forms by modeling rather than having a high temperature mold to hold the glass. http://www.glassclay.com/ pate de verre 1 2 2011-07-23
Graphite
A form of carbon that takes the form of flat plates that slip easily over each other, thus making a lubricant.  In glass work graphite is used for blocks and paddles because it makes a smooth surface.  It conducts heat very well, so it does not chill the glass as much as marble or metal might.  It also conducts electricity.  It can be used for molds, with care, because if held at too high a temperature it will sublimate or burn.  2006-10-03
H
Hydrofluoric Acid
VERY DANGEROUS "A volatile, colorless and highly corrosive acid used as an agent to etch glass.  Pure acid dissolves glass leaving a bright surface [used for cutting back a design]  Mixed with sulphuric acid it produces a high gloss on lead glass; mixed with ammonia, the neutralized acid leaves a frosted finish." Collectors Encycl.of Am.Art.Glass p.226  MF: DANGER: HFl silently penetrates exposed skin and begins attacking the bones, only causing pain when too late and requiring extreme measures of calcium ingestion to save life.  Fluorine gas is a lung damaging toxic material. 2008-05-21
I
Ingredients
Among the ingredients of glass are Sand, Limestone, Potash, Soda Ash which are also discussed the mixed product batch
Insulating Castable
Castable Refractory with insulating values similar to insulating fire brick
Insulating Fire Brick IFB
A lightweight fragile fire brick that insulates against high heat. Will withstand various max. temps up to about 2500F, while non-insulating firebrick can be had up to 3500F Refractory
Investment
A white powder mixed with water to make high temperature molds for metals (and glass). After heating it washes off the piece. Metal Molding 2003-02-05
J
K
L
Latex
A white thick liquid containing natural rubber in unvulcanized form that can be brushed on in thin layers to build up a mold around an original, the mold then can be used to make copies.  The dried latex is amber in color, is flexible and reasonably tough.  Used for plaster copies, sulphides, and silica/plaster molds. 2003-02-05
Lead Oxide, Lead (PbO, Pb
When added to glass, most often clear crystal, gives a weight to the glass which makes for a clear ringing tone when struck and a brilliant reflection when cut. Also extends the working range of glass, so colors often have a considerable percentage of lead so they will work with a wider range of COE. Lead is considered a health hazard and must be tested for on food surfaces in California in particular. Lead in glass is less risky than lead paint which is less risky than exposed lead in stained glass came and some solder.  "the U.S. safe limit of 0.06% for paint. Lead is a neurotoxin.  It causes damage by mimicking helpful metals found naturally in the body, such as calcium, iron and zinc.  Lead displaces those and distupts brain circuits. ... New research suggests there is no safe level of lead exposure." Wall Street Journal, Aug.3 2007 p A5. Litharge  Red Lead
Lime, Limestone (Calcium Carbonate)
An basic ingredient in glass making when mixing batch. Counter-balances soda ash or potash which lowers melting point but increases ease of attack on the glass by water.  Further information at batch.htm
Litharge (PbO)
Lead monoxide.  Lead oxide
Lithium carbonate (LiCO3)
An ingredient in glass making when mixing batch. Further information at batch.htm
M
Metal
In the jargon of the craft in the glass factory the stuff worked which avoids any confusion with "get me a glass" and "put up the glass we blew this morning", thus "we had good metal by 8 am today"  White metal is clear glass; opal is opaque white glass.  2008-05-21
Metal Oxides Metallic Oxides
When a list refers to the color supplied by selenium or cobalt or the qualities of adding lead, it should be understood that always a salt or oxide of the metal is referred to not the pure metal (with the odd exception of gold).  Cobalt may be added as cobalt oxide or cobalt carbonate.  These mix with the silicon oxide (sand) that forms the bulk of glass mix. 2008-05-21
Mud
The name for the strange mixtures of wax, oil and solvents to coat jacks, especially the old iron ones (modern ones are stainless steel) to reduce chatter and chill marks and make for smoother working.  Plain beeswax or carnauba usually works fine.
N
Natural Gas
One of two common fuels, with propane, used in glass blowing studios. Glass factories have often located to take advantage of local availability of natural gas, thus northern Ohio and West Virginia.  Natural gas is delivered at low pressure in most urban areas and at higher pressure in industrial areas.
Newspaper
Used for shaping glass when formed, wetted and held in the hand, to replace a mold or block. More
Nitre
Sodium Nitrate, used in making glass.  Forms small bubbles into large to fine the glass.
O
Obsidian
A glass made in volcanic flows under proper conditions. As a glass, it has no preferred cleavage and thus flakes off in conchoidal form, forming very sharp edges with a thick center for weapons and tools used by natives. A mixture of about 75% Silicon Dioxide with Iron and Magnesium oxides.  Deteriorates in presences of water to form perlite. WikiRef  Because content varies, so does melting point, but behavior and temperatures reported suggest it behaves like borosilicate glass, not melted at 940C (1724F) and melted and deformed but not flattened at 1080C (1976F) Src, copy on file  2009-09-24
Oxygen
A gas found in the air and an element found in many compounds. Necessary for life.  Used to make flames burn more intensely than with air which is 80% nitrogen that does not assist burning.  Commonly used in torches with acetylene for welding and with propane or natural gas for glass, required for working borosilicate. Occasionally used to boost heat in furnaces. Supplied in dewars, in high pressure tanks, and by generators. 2009-07-26
P
Paper
Paper is used in the form newspaper for blocking, in rolled up rods for pacioffis and of course in support good old reading material and pictures of glass. 2006-06-29
Parison
name for shaped blob at end of pipe in early working stages.
Perlite
Used as a refractory insulator by glass workers. A fluffy white volcanic glass product which is expanded by heat and sold cheaply at garden supply places as an aerator for potting soils and also used as a lightweight aggregate for concrete and plaster. "A lightweight material prepared from volcanic lava,..."  Perlite Institute - Basic Facts about perlite
Plaster of Paris
A white heavy powder that, when carefully mixed with water, produces a creamy thick pourable mixture that can be used to make molds which can be used to make copies of the original.  Once set, plaster of Paris is insoluble in water.  For more information see Metal Casting. Do not buy more than can be used in a few months as the powder absorbs moisture from the air and loses its ability to set. Other materials called plaster exist.  2003-02-05
Potash, Potassium Carbonate (K2CO3)
An ingredient in glass making when mixing batch, an alternative to soda ash. Further information at batch.htm
Propane
One of two common fuels, with natural gas, used in glass blowing studios. More commonly used in rural areas where natural gas is not available, may be okay (as in Dallas) in a large tank where natural gas delivery is inadequate for glassblowing.  A mixture of petroleum compounds that liquefy under slight pressure and become gas at room temperatures.  Supplied in thin wall metal tanks or delivered and stored in larger tanks.  About 250 psi in storage, reduced by regulators for use. 2009-07-26
Q
Quartz
The crystalline form of silicon dioxide found in rocks from which sand comes by erosion.  Melts at a very high temperature and can be worked like glass to give vessels for processing semiconductor material.  Requires special torches and eye protection to work. 2004-12-07

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R
Rammable Refractory
A product delivered in a heavy paste form that is applied and hammered (rammed) into place by hand or jack hammer. Glass workers usually use it for lips of furnaces and bottoms and use a 3# sledge or similar hammer to mold/merge it solid. In industry it is used for repairing and building up high abrasion locations and some can be applied while the location is relatively hot (several hundred degrees, not a couple of thousand.) 2001
Red lead (Pb3O4)
Form of lead used to make flint glass. "bright red to orange-red powder, also called minimum, that is used in the manufacture of storage batteries, lead glass, and red pigments; a paint made with red lead is commonly used to protect iron and steel from rusting. Chemically, red lead is lead tetroxide, Pb3O4 , a water-insoluble compound that is prepared by the oxidation of metallic lead or of litharge (lead monoxide); the commercial product sometimes contains litharge as an impurity."  Lead
Refractory
Any material that withstands the high heat needed for melting glass (also steel, etc.), the two most common being clay and ceramic fiber substances. Special clays fire up to form bricks that do not deform in the heat. If previously fired clay (grog) and organic material is added to the mix, insulating firebrick is created by the empty spaces in the fired clay. Ceramic fiber is a result of space research and insulates. Two other refractories, known to gardeners, and sometimes used as insulation are vermiculite, which is expanded mica, and perlite, from lava.  Refracto.htm
S
Sand
Mostly silicon dioxide in the form of quartz. An ingredient in glass making when mixing batch. Further information at batch.htm  Pure white sand has very low iron content which is desirable for making glass without color. 2004-12-07
Silica (SiO2 melt:3133F)
The pure form of silicon dioxide, also referred to as silica flour.  Usually a fine white powder, it is used in foundry work for making thin shell metal casting molds with colloidal silica, a liquid suspension in water. Silica is damaging to the lungs.
Silicon (Si  sg:2.33  melt:2605F)
The element, one of the most common on earth, that makes glass as the oxide and in very pure form (99.999999999%) forms the basis for the modern semiconductor industry.  As much as you ever wanted to know 2004-12-07 Not silicone
Silver Leaf, Foil, Metal  (Ag  sp:10.49)
Pure metal, used for inclusions and decorations on glass as well as being worked with jewelers methods and formed around the glass.  Leaf is very thin, foil is thin, the latter being more common in glass work because discoloration near the melting point of silver (1761F) which is lower than molten glass. 2004-12-07
Silver Nitrate, Chloride, & Bromide (AgNO3, AgCl, AgBr)
Chemicals used to color glass, especially to provide a silver sheen to the surface when the salt is reduced to the metal after application.
Slag
Slag is broken chunks of glass which are usually the result of dumping or breaking up a furnace or pot.  Because of odd thicknesses and harsh edges which catch the light, it has been used for decorative purposes for centuries.  Could be used like cullet but normally is not as it is the remains of a large mass of glass and is not consistent or easy to handle. Sold by Gabbert Cullet and through rock/lapidary outlets.  2009-02-25
Soda (Sodium Carbonate, NaCO3), Soda Ash
An basic ingredient in glass making when mixing batch. Further information at batch.htm
Sodium nitrate (NaNO3)
An ingredient in glass making when mixing batch. Further information at batch.htm  Forms small bubbles into large to fine the glass.
Sodium Silicate, Water Glass
A thick clear liquid (as used) available from pottery supply places, used as glue and rigidizer for frax and in making sand casting molds. It gets hard on exposure to CO2 in air or directly. A mixture of silicates with the general chemical formula xNa2O.ySiO2, forming a clear viscous solution in water. xrefer - water glass (or sodium silicate) [NaO2 3.22 SiO2 Initial acidification of a water-glass (sodium silicate) solution yields Si(OH)4" Colloidal Silica]
Steel
Ordinary steel angle and tubing is used to construct equipment while stainless steel is used for pipes and punties and for containers.
Styrofoam
Used to make cores for casting furnace domes and for casting glass.  Styrofoam is a (usually) white puffy plastic that comes in two forms - bead board and cellular foam.  Bead board is far more common these days because it can be made in a simple mold (cardboard box if need be) by adding steam to hard pellets which expand and stick together. It can be recognized by the small balls of plastic that are shed and the circles showing on the surface.  Cellular foam has lots of "air" spaces and is less available because to make it requires a leak proof box that will contain the expanding foam to restrict the bubble size.  The bubbles are made chemically or can be done with a large air mix.  Requires a central installation.  Both types are usually scrounged by glass workers.  The board is used as insulation in flat pieces and furniture and computers come packed with the stuff - it can be glued with white glue into bigger blocks. 2003-02-16
T
Tin Chloride (SnCl)
One of the chemicals sprayed or blown on hot glass to iridize the glass, producing the sheen like glass long buried in mineral rich soil.
Tin Oxide
When added to glass batch produces opaque white glass. Further information at batch.htm
U
V
Vermiculite
Used as a pourable refractory insulator and component of insulating castable. A fluffy dark gray product made by heating a variety of micacaous minerals and sold cheaply at garden supply places as an aerator for potting soils; also used as insulation and as a passive annealer for lampworking. Rumored to contain fine asbestos particles but true only in distant past of one mine..
Viscosity
A measure of the thickness or pourability of liquids.  An important factor in working and annealing glass Discussed here
W
Wax
A category of material mostly characterized by a melting point below the boiling point of water with a glossy surface and a "waxy" appearance. Most are water repellent and are used for protective coatings, shiny appearance, and slippery movement. Waxes used in glassblowing include beeswax and carnauba for tool edges, and casting wax for lost wax molding. 2003-02-05
Water Glass
See sodium silicate
White Glue
Usually means common woodworkers glue, like Elmer's Brand that is not particularly waterproof.  Besides wood, it can be used to glue Styrofoam and is used to hold glass pieces in place for fusing. glues.htm
Wood
Used to make tools which stand the heat because the wood is soaked in water until water logged and further lifted from water just before use, so coated with water. Blocks, Paper & Wood
X
Y
Yellow Glue
A woodworking glue that is more water resistant and stronger than older white glue.  It is not water proof and joints will come apart if soaked in water.  Can be used to glue Styrofoam, but leaves a tougher joint to attack when shaping.  glues.htm
Z
Zinc oxide
An ingredient in glass making when mixing batch. Further information at batch.htm
Zircon
A refractory material used to seal surfaces of other refractories, to repair cracks in burner heads, and for lost wax casting of glass and bronze.  Zirconium  oxide is available as a slurry for coating models and painting on surfaces and as a powder to add thickness to casting shells.

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