The
object of this technique is to make a shaped piece without use of a
refractory mould. It is applicable to small items.
You
can use jelly, soap, candle, etc. moulds. They can be rigid or
flexible. They should be without undercuts and have a draft, which is
why jelly, soap, and candle moulds are so suitable. Be careful of
the size, as a large amount of frit can be required even for a small
mould.
Some
people use only powder for this process. I use a 50/50 combination of
powder and fine frit. You can use clear frit with powder. If you do
so, you need to measure out the appropriate amounts. Then put the
frit and some water into a container with a closure. Close and shake
to wet the frit. Then add the powder and shake again to ensure the
powder adheres to the frit. Once thoroughly mixed, add more water to
make a thick slurry.
Pack
the mould with the mixture. Then using absorbent paper towels firmly
pat the contents of the mould as dry as you can. Place the mould in
the freezer for at least a couple of hours, or for large ones
overnight.
When
frozen, remove from the mould and place on the kiln shelf. The shelf
needs a separator which can be kiln wash or fibre paper. Some leave
the piece to thaw out and some more of the water to evaporate.
Whether
you fire immediately or let the piece thaw and evaporate, you need to
fire slowly to 100C and soak there until no more moisture is evident
to avoid creating pockets of steam that will blow the piece apart.
After that you can fire as normal for an initial firing of a two
layer piece.
The
piece will shrink a bit during the firing, but it is safe to anneal
for the original thickness of the frozen piece. If you have a large
piece or one with lots of variation in thickness, you should use at
least the next thickness up from the Bullseye tables for annealing
thick pieces. Sometimes you should use two steps up.
Further information is available in the ebook Low Temperature Kiln Forming.
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