Cooking Glass Glossary

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 'Glass'

Compounds of silica (sand) and other materials. As silica is always the major ingredient, the type of glass is often defined by the other ingredients, thus soda lime.

 Acid etching

Surface treatment for glass using hydrofluoric acid or ammonium bifluoride to remove areas of the glass. A potentially hazardous process.

 Air volume expansion ratio

Ratio of the volume of air heated to a given temperature to the same mass of air at standard temperature pressure. (20C at sea level)

 Alumina

Aluminium oxide (Al2O3), Fine white powder. Refractory material. Can be used as battwash ingredient and as a bedding powder.

 Alumina hydrate

(Al2O33H2O) A fine white powder used as a major ingredient in batt wash and as a bedding or texturing agent. Shrinks on the first firing when water of hydration is lost.

 Ambient temperature

Prevailing external or room temperature.

 Ammonium bi-fluoride

Glass etching material. Toxic by inhalation. Declared as a potentially hazardous material in concentrations 10% and above.
Active ingredient in 'Etch-all', a proprietary product. As the concentration in that product is 20% there are restrictions on its storage or sale. See Etch-all.

 Amorphous

Without order. The glassy state.

 Analogue pyrometer

A combination thermocouple and analogue indicating (pointer moving over a scale) meter for measuring temperature. Self powered. Meter is calibrated to a connecting lead of a specified length. Any other length will produce calibration error.

 Anneal cool

Second stage of the annealing process in which glass is cooled from anneal soak temperature to below the strain point; at a rate proportionate to its thickness and mass.

 Anneal soak

Process of holding glass at a uniform temperature so that the temperature will equalise throughout the piece before cooling proceeds.

 Anneal soak point

Upper limit of annealing zone (range). (Assumed to be 5 to 10 degrees C above theoretical annealing point, which is an arbitrary temperature that corresponds to a viscosity of 1013 poises for the particular glass and where stress in glass is relieved in a matter of minutes.)

 Anneal soak time

A period proportionate to the thickness mass and type of glass. Should be of sufficient duration to allow near equalisation of temperature throughout the glass.

 Annealing

The process of controlled cooling of glass to prevent the building-in or retention of residual stress.

 Annealing kiln

Kiln for annealing out-of-kiln formed objects such as beads or mouth blown pieces.

 Annealing point (theoretical)

An arbitrary temperature in the annealing range that corresponds to a viscosity of 1013 poises and where stress in glass is relieved in a matter of minutes.

 Annealing temperature

Temperature at which stress in a glass is relieved in the shortest time: generally 5C to 10C above theoretical annealing point.

 Annealing zone (range)

A zone through which the glass is cooled at rates appropriate to its thickness mass and type. It comprises of two steps; anneal soak and anneal cool.

 Antique glass

Mouth blown glass cylinders slit and flattened into sheet form. An original method of sheet glass making. Now used only for highest quality stained glass.

 Battwash

Term used to describe a wet coating for kiln shelves and moulds to prevent glass sticking to them.

 Bead making

A torch or lamp working process in which glass is heated in a flame and then wound onto a coated wire rod. Can be a single layer of colour or multiple layers of numerous colours. Finished beads must be annealed in a kiln.

 Bedding powder

Fine refractory powder placed on kiln shelves or flat surfaces to impart texture or pattern to fired glass.

 Bending glass

Heating glass to a temperature high enough to cause it to conform to a mould or pattern, but low enough that surface texture and clarity will not be affected.

 Bentonite

Dense clay of volcanic origin which swells when wetted. Thixotropic. Takes time to swell. Improves brushability of battwash.

 Bisque (biscuit) firing

First firing of clay to remove moisture and achieve solid but porous form.

 Borosilicate glass

Type of glass containing boric oxide which enables it to withstand extreme thermal shock. Used for cookware and scientific equipment.

 Bubbles

1. Gaseous inclusions in glass: can be minute and widely dispersed or larger due to agglomeritisation (joining together).
2. Eruptions in sheet glass during a fuse firing, due to expansion of air trapped between the sheets.
3. Eruptions in sheet glass during a slump firing, due to expansion of air trapped between the sheet and the bedding powder or to gasification of bedding material.

 Burst firing

Applying power to elements in short bursts. Usually done with Solid State Relay (SSR), rather than with contactors or power relays which require longer cycle times.

 Calcining

The process of removing organic matter and chemically combined water by heating.

 Came

Extruded lead or zinc strips, usually H shape, for assembling leadlight or stained glass panels.