Texture moulds are essentially
permanent kiln carving moulds. These are
moulds that use different levels within the mould to develop the imagery by
giving different thicknesses to the glass. Temporary or single use moulds can
be made from fibre paper, although not with the same subtlety as the ceramic
ones.
Single layers
Many people wish to use a single
layer in these texture moulds. For a single layer, a tack fuse is a high as you
can take the temperature. This will not give you the definition that you could
get with higher temperatures unless you use very long soak times.
Good definition
To use higher temperatures, you need
at least two layers (6mm) to avoid distortion, dog boning, possible bubbles and
needling. With two layers you can go to
full fuse temperatures to get the best conformation to the mould.
Low temperature firings
You can get better definition at
lower temperatures by going slowly to your target temperature. This slow rise
in temperature – ca. 100C - or less - per hour – all the way to the lower end of the tack
fuse range – ca. 730C to 750C - needs to be
combined with a long soak, possibly two or more hours. This long soak allows the glass to sink into
the depressions of the mould without shrinking, dog boning or needling. This shows that the speed you use has a major
effect on the target temperature.
Separators
Another element of difficulty in the
use of these moulds is the separator used. Kiln wash is adequate, especially if
you are using the lower temperatures.
Boron nitride is a popular choice for those going to higher
temperatures. Using iridescent glass
with the coated side down to the mould provides an additional separator, allowing
higher temperatures to be used. It can
enhance the appearance of the piece too.
The way you schedule for texture moulds is an interaction
between the thickness of the glass, the rate of advance, the target temperature
and the kind of separators used. With these four factors interacting, the
choices are not simple.
More detailed information is available in the e-book: Low Temperature Kilnforming.
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