Warm glass
Fusing is the use of heat to join the glass by fusion welding, either with or without an associated change in shape, depending on the temperature.
These moulds are usually commercially made and are offered in a range of standard shapes and sizes: bowls, trays etc.
The hot glass otherwise forms a good seal with the lip of the mould and an air bubble is trapped.
Such a trapped bubble often causes problems - when cooling this air may contract to form a partial vacuum that is enough to break the glass.
Kiln wash or ZYP Coatings' Boron Nitride Aerosol Lubricoat is used beforehand, to prevent the glass sticking to the mould.
If a kiln shelf is placed beneath the ring mould, this catches the falling glass and gives a vessel with a flat base.
Draping is a variety of free-fall slumping, where the mould former is placed in the centre of the piece and the outer edge falls under the heat.
Variations in the glass are thus preserved in the final piece, so colours and inclusions present beforehand may still remain in the cast item.
Pâte de verre (literally glass paste) is cast from powdered frit, mixed with a glue binder.
[1] Warm glass working is similar to that for ceramics, in that a piece is assembled, placed into a cold kiln and then heated through a pre-defined cycle, including a slow cooling phase afterwards.
The reason for this is the extra control accuracy and programmability available with electric heating,[6] as well as their lower capital cost and convenient installation.
As firing cycles extend over several hours, potentially days for large architectural pieces, automatic unattended control is obviously important.
[6] Controllers dedicated for glass kiln use have their entire heating cycles defined before use with multiple set temperatures, hold times and ramps between them.
The most sophisticated controllers of all are dedicated to glass use and allow pre-defined cycles such as "Fuse" or "Slump" to be selected from a simple menu, without their operator needing to be aware of the precise temperatures required.
