Wednesday, 25 April 2012

Separators for Steel

Steel moulds, whether stainless or other steel, require separators as glass will stick to hot metal.

The preparation of steel is a little different from ceramic or fibre moulds. First the steel has to have the oil coating removed. This can be done by sanding, sandblasting or by heating to about 550C.

The separators can be just normal kiln wash, boron nitride, or fibre. When using kiln wash or boron nitride, the steel needs to be heated – about 200C should be enough. Too hot and the water will boil leaving gaps in the coating. If the metal is too cool, the kiln wash will drip. A little experimentation will be needed to find the right temperature for your purposes. Remove the mould from the kiln and brush or spray on the separator. Return to the kiln to heat up again and apply the separator again. Continue this until an even complete covering of the metal has been achieved. It does not have to be thick.

Fibre paper works best on cylinder or wave moulds with curves in one plane only.  Bowl shapes lead to wrinkling of the fibre papers and marking of the glass with wrinkles.  This applies to the Bullseye Thinfire too.

Just as on shelves and ceramic moulds and as long as you fire below 700C, you can use the coated mould over and over with no problems. Once you fire hotter than 700C, it is best to remove the old kiln wash and put a fresh coating on before firing again.