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Words beginning with G
Glass
A glass is actually a "super-cooled liquid", it is the opposite of a "crystal" in which molecules have opportunity to orient themselves in the preferred pattern during freezing. In a glass the random orientation of molecules is frozen into the solid.
"Ceramics for the Potter "University of Toronto Press" 1952 called it "silica and two or more bases, which are combined under heat to form a molten solution. On cooling, the solution becomes so viscous that the molecules cannot move about freely enough to form crystals before the state of rigidity is reached. If glass were allowed to cool slowly, it would be as crystallized and as opaque as granite - it is the fast cooling, with the viscosity, that makes glass transparent. Glass is, in short, a solid solution."
In 1945 the American Society for Testing Materials suggested the following definition if glass: "Glass is an inorganic product of fusion which has cooled to a rigid condition without crystallizing."
In 1962 the British Standards Institution adopted the same phraseology.
Later more complex methods of producing this state led to revisions such as:
"Glass is a non-crystalline solid" and....."glass is and x-ray amorphous material which exhibits the glass transition.."
See "Ceramics Glaze Technology" for more information.Glaze
A thin glassy layer formed on the surface of fired ceramic. Glazes are a finely ground mixture of mineral and man-made powders tuned to melt and flow at a specific temperature. Many clays will melt well at higher temperatures and thus qualify as 'slip' glazes. Glazes are normally mixed with water, suspenders, and hardeners to make them harden on drying and produce a suitable consistency for application by painting, dipping, or spraying.
Glazes are often classified (e.g. unleaded, raw, fritted) to designate type within a specific industry or type of ceramic ware.Glaze fit, glaze body fit
The relationship between the thermal expansion of body and glaze. Ideally a glaze should have an expansion that is slightly lower than the body so that contraction during cooling puts the glaze under compression and thus prevents crazing.Glossy
'Gloss' refers to how shiny and light-reflective a glaze is. Glazes high in glass former (SiO2, B2O3) are glossy. Those high in Al2O3 tend to be matte. Fluid glazes can crystallize to a matte surface if cooled slowly or a glossy surface if cooled quickly. The SiO2:Al2O3 ratio is taken as a general indicator of glaze gloss, ratios of more than 8:1 are likely to be glossy.Grog
A granular material made from crushed brick, refractory rock, or other pre-fired ceramic product. It is added to bodies to reduce drying and firing shrinkage and thermal expansion, increase stability during firing, and to add texture.
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