## Anneal: A process used to cool formed glass at controlled temperature rates to prevent thermal stresses. ### BTU: A British Thermal Unit (BTU) is the amount of heat energy needed to raise the temperature of one pound of water by one degree F. This is the standard measurement used to state the amount of energy that a fuel has as well as the amount of output of any heat generating device. You might be able to imagine it this way. Take one gallon (8 pounds) of water and put it on your stove. If the water is 60 degrees F. and you want to bring it to a boil (212 degrees F.) then you will need about 1,200 BTUs to do this. British Thermal Unit (BTU) is the measurement of heat created by burning any material. Combustible materials have a BTU rating. Propane has about 15,000 BTUs per pound. ### Borosilicate Glass: A glass whose main constituents are Silicon Dioxide (SiO2) and Boric Oxide (B2O3). Corning Laboratories developed borosilicate glasses in the early 1920s in response to a need for chemically resistant glassware for laboratory work. It is commonly found in the home today in the form of coffee pots and oven cookware. The properties that make this glass valuable are its extreme resistance to chemicals (even the harshest acids do little damage to the glass or its appearance) and the ability to undergo sudden temperature changes without fracturing. ### Chromophore: Coloring agents can be very powerful. 1 atom in 10,000 atoms of clear glass may be enough to produce the illusion that the glass is blue. This grouping is called a “chromophore.” ### COE (Coefficient Of Expansion): A measurement of how far the molecule within a given substance expands and contracts when the substance is heated and cooled. COE is one of the important factors (although, not the only factor) that determine compatibility between two glasses or substances. COE is also known as Coefficient of Thermal Expansion (CTE) and Liner Expansion Coefficient (LEC). ### Colloidal: Finely divided particles trapped in between other particles so they don’t sink. ### Colorant: Usually an insoluble powdered substance used to produce a desired color or hue. we ### Crystals: Formed by the solidification of a substance. Crystals have a regularly repeating internal structure, external plane faces, and can be 4, 5 or more sided. ### Dichroic: Dichroic means two colors, and this glass appears to be different colors when viewed from different angles or in varying degrees of illumination. Dichroic glass is created by adding a thin layer of metallic oxides which transmit certain light wavelengths while reflecting others, causing an iridescent effect. ### Devitrification: 1: To deprive, wholly or partly, of vitreous character or qualities; 2: to undergo a change in texture from glassy to crystalline. ### Fire Polish: A technique used to eliminate surface flaws and increase the overall strength of the glass, thus preventing future cracking. The glass is heated in a soft flame at temperatures just below softening point, around 1400°F. Only the surface is heated, so that the work piece does not lose its shape. At this temperature, the surface of the glass can move small distances to eliminate surface imperfections. ### Flashback: When a flashback (backfire) takes place in a mixing chamber, unless you shut off the oxygen valve, the flame burning in the torch head may ignite gases in the hoses and result in a flashback. A flashback is an explosion that progresses through the torch, hoses, regulators, and into the cylinders. ### Frit: Ground glass, ranging in particle size from gravel-like to a fine powder. Frit is sometimes used as a raw material in glass manufacture, and sometimes as a coloring agent or for decorative effect in hot glass crafts like lampworking, blowing and fusing. ### Fused Glass: When heated to the proper temperature, two pieces of glass will flow into each other so that upon cooling they form a single unit. The two pieces need to be compatible. ### Fusing: Glass-fusing is the process of using a kiln to join together pieces of glass. ### Garage Door: I door in the front of a kiln for the quick placement or removal of work from inside. Usually includes a rod rest on the outside for punty support. ### Hard Glass: These are glasses that are characterized by having a high softening point in the range of 1900°F to 2200°F and need a great deal more heat to manipulate. Borosilicate glasses generally fall into this category. ### Nucleate: In assembly reactions were the first steps are energetically less favored; the reaction is much faster if a pre formed seed is used to nucleate growth. ### Nuclei: A seed on which crystals can grow. ### Opal or Opalescent Glass/Opaque: Any glass into which a material has been introduced at the raw materials stage, causing a degree of crystallization to occur and creating opacity in the glass. The degree of opacity is variable, depending upon composition and temperatures used in the manufacturing process. ### Parking: Placing an in-progress work in an annealing kiln. This can be done to stabilize the temperature within the piece or just hold it until it is needed. ### Polychromatic: Term used by GA to indicate that a cane can develop many different colors or even multicolored metallic sheens on the surface of the glass. ### Powder: Glass that has been crushed to a size that resembles wheat flour. ### Pre-Mix Torch: A torch in which oxygen and fuel are combined within the body of the torch before being expelled and ignited. These torches can produce very hot, sharp, and high velocity flames. ### Pyrex™: The brand name for a class of borosilicate glasses developed by Corning Laboratories. ### Pyrosols: The precursors to chromophores; colorless. ### Redox (Reduction-Oxidation Reactions): An oxidation-reduction reaction is a reaction where electrons are transferred between two reactants. The substance that is oxidized is called the reducing agent. The substance that is reduced is called the oxidizing agent. Historically, oxidations were first defined as the combination of oxygen with some other element or compound; reductions were defined as the loss of oxygen from a compound. This simple definition works fine for the loss of oxygen from a metal oxide in the smelting process, which is very similar to what happens during lampworking. ### Reduce: Some artists enjoy this effect, others don’t. For example cobalt colors can go gray, while copper greens and blues can develop brick red streaks. To mitigate this, adjust the propane in your flame (decrease it) and use an oxygen rich flame. ### Soda-lime Glass: A glass whose main constituents are Silicon Dioxide (SiO2), Sodium Oxide (Na2O) and Calcium Oxide (CaO). Sodium Oxide is called Soda Ash in its raw form and Calcium Oxide is likewise called lime, hence the name “Soda-Lime.” This type of glass formula is as old as glassmaking and lends itself to broad industrial uses due to its inexpensive material costs and ease of working in its molten form. Most decorative art glasses are made from this general formula and can be found around the household in the forms of drinking glasses and plate glass windows. Soda-lime glasses are not very chemically durable and are subject to fracturing from quick thermal changes. ### Soft Glass: These are glasses that are characterized by having a low softening point in the range of 1200°F to 1500°F. Soda-lime glasses generally fall into this category. ### Stone: A general term used to indicate an inclusion that is a different composition from the surrounding glass. Typical stones come from furnace ceramics and under melted chemicals used in glass making. ### Stringer: Thin glass strings, most commonly used for inside/out or trail and rake applications. ### Striking: Indicates that a second “heat” brings out the color. The final color is affected by the duration and environment (oxidizing/reducing) of the second heat. Oven striking is usually at 1075°F. Rubies generally require more time than silver colors. If striking a piece that has both colors, you can pre-strike the rubies in the flame or work the silver colors very hot, so that there is no color development prior to placing in the kiln. ### Sublime: To pass off in vapor, to volatilize from the solid state without apparent melting, said of Cadmium, which does not exhibit a liquid form on heating. ### Surface Mix Torch: A torch which mixes oxygen and fuel at the surface of the torch face. These torches produce softer and larger flames. ### Thermal Expansion: Change of material size as a result of temperature change. ### Tinted Glass: Transparent glass with a consistent color throughout. ### Transmittance: Ratio of light or heat that can pass through the glazing surface. ### Valance (Valance State): This is a somewhat outdated concept in chemistry. It is a number that tries to predict with how many neighboring atoms a certain atom can form a chemical bond with. For redox reactions, it has been superseded by the concept of oxidation number. ### Viscosity: The property of a fluid that resists the force tending to cause the fluid to flow. The lower the viscosity, the runnier a fluid is. Water has a very low viscosity, honey a higher viscosity and a cooled glass a very, very high viscosity. ### Vitreous: Of the nature of, or resembling, glass.