Anneal – A process used to cool formed glass at controlled temperature rates to prevent thermal stresses.
Annealing Range – Determines the limits of temperature within which glass may be annealed.
ASTM – An acronym for American Society for Testing Materials. ASTM is a not-for-profit organization that defines the physical properties of materials and testing methods so manufacturers and consumers share a common standard of material behavior. Their efforts are not limited to materials but also define common standards for services, systems and products.
Aventurine – A super-saturated chrome solution (>1%), slow cooled so that the chrome precipitates out as platelets. These platelets provide the sparkle and are called aventurine. 1) If using a green chrome color and you anneal it at too high of a temperature, or slow cool it, you can cause aventurine to form. In almost all cases, this will lead to cracking of the piece. 2) In the GA Sparkle series, the chrome has been fully precipitated to provide you with an extremely stable sparkle-containing glass for your working convenience. 3) Precipitates of other metals, such as copper, are not called aventurines.
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.
Batch – A quantity of raw materials (colorant, silica sand, calcium, and various oxides) properly weighted and mixed to be introduced into the glass furnace where they are melted at 1500°C.
Blister – A cavity in glass filled with gas
Borosilicate Glass – A glass whose main constituents are Silicon Dioxide (SiO2) and Boric Oxide (B2O3). Borosilicate glasses were developed in the early 1920s by Corning Laboratories 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.
COE – An acronym for Coefficient of Expansion. Also known as Coefficient of Thermal Expansion (CTE) and Liner Expansion Coefficient (LEC).
Carnival – A base color that is designed to develop a full spectrum (ROYGBIV) of color in the torch. The base color affects the overall appearance.
Celsius – Temperatures expressed with the Celsius scale are based on a division of one hundred degrees between the freezing point and boiling point of water.
Chemical Saturation – The colorants range from 0.05% to 7%. The more colorant added to create the color, the less likely the rod will behave like clear glass. Since the compatibility of the glasses is dependent on factors – such as, the glasses having similar cool-down rates, from high to low temperatures, and the viscosities in two (or more) glasses at the same temperatures be the same—it stands that the higher the saturation of colorant, the greater the possibility of developing internal stress in the work piece. Knowing that a color has a high saturation of colorant helps decision-making regarding order of application, annealing cycles, and much more.
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.”
Clear Glass – A colorless glass.
COE or 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.
Colorless – A property glass exhibits in the absence of coloring pigments and light is transmitted through the mass unchanged. Also known as crystal or clear glass.
Compound – A substance formed from two or more elements that are chemically united in fixed proportions.
Crusher – A device that uses hammers or rotating drums to pulverize a material into smaller fragments. This is used in glass manufacturing to produce cullet, frit and powder.
Crystals – Formed by the solidification of a substance. It has a regularly-repeating internal structure, external plane faces, and can be 4, 5 or more sided.
Cullet – Recycled glass used in the manufacture of new glass.
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.
Divitrification – 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.
Flux – A substance that aids, induces, or otherwise actively participates in fusing or flowing. A chemical additive that lowers the required melting temperature during the manufacture of glass or improves the flow during fabrication.
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.
Glass – Any substance having a non-ordered, non-crystalline molecular structure when cooled to a point below transformation temperature (Tg). Most common glasses are silica-based and melted with soda, lime and sometimes other components (boron, alumina and potassium). Most glasses are also hard, shiny and transparent or translucent.
Glassworker – An individual who forms glass into various shapes and objects. This term generally applies to the working glass in its hot, liquid form.
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.
Ionic Colorant – These elements are found in the transitional area of the periodic chart and include such metals as cobalt, chrome, manganese, nickel, copper and iron. The ionic colors can exist in several oxidation (or valance) states and provide the lampworkers with several different colors. This is why your copper-green rod can give you red streaks when your flame is reducing in nature.
Lampworker – A glassworker that manipulates glass rods, tubes, frits, and powders by heating them in a high temperature bench torch (a high powered Bunsen burner) to produce objects. This is in contrast to other glassworkers who produce objects by gathering or ladling molten glass out of a melting furnace.
Lehr – Pronounced “Leer,” is an oven of various designs that slowly cools glass objects from forming temperature to room temperature. Glass's property of low heat conductivity makes it very vulnerable to quick temperature changes and produces stresses that fracture the object. Slow cooling allows the heat to be dissipated evenly throughout the entire mass and avoids producing stress. Lehrs vary in design between a simple box that is cooled by a digital controller, to massive devices where the glass travels on a steel mesh belt through zones of decreasing temperature.
Luster – A base color that is designed to develop a partial spectrum (YGBIV) of color in the torch. The base color affects the overall appearance of the multicolored sheen.
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, which causes a degree of crystallization to occur, creating opacity in the glass. The degree of opacity is variable, depending upon composition and temperatures used in the manufacturing process.
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.
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 the cobalts 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.
Refractory – A dense ceramic material commonly used for high temperature applications.
Rod – Glass that is in the form of a thin cylinder that resembles a long pencil. The dimensions of this shape are 3/16" in diameter by 10" long.
Seed – A term used by glassworkers to identify tiny air bubbles in a glassy body. Small air inclusions are very undesirable by glassmakers and consumers.
Skystals – With silver colors, this is the purposeful development of crystals on the surface of the glass only. Unplanned or uncontrolled growth on the surface is referred to as haze or scum.
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.
Softening Point – The temperature at which a glass loses enough viscosity that it stops acting like a brittle solid and begins to flow like a liquid.
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.
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.
Stringer – Thin glass strings, most commonly used for inside/out or trail and rake applications.
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.
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.
Tube – In this document, glass that is in the form of a thin pipe that resembles a long drinking straw. The dimensions of this shape are between 1/2" to 3/4" outside diameter with a wall thickness of 1/32" and 20" long.
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.
Wipe On/Wipe Off – Sometimes called “double wipe” is a method where glass is first applied to a surface and while still soft the application rod is pulled back through the glass and pulled away from the surface. The technique is used to create fish fins, bird wings or similar structures.
WYSIWYG – What You See Is What You Get. Used to indicate a color that is stable and not influenced by the flame adjustment (oxidizing or reducing).
