Assertion
There
is a common assertion that you need to extend the annealing - or temperature
equalisation soak - on each firing after the first.
The
rationale for this is never fully explained.
Possibly it comes from the fact that you need to reduce the rate of
advance on already fused pieces over the unfused lay-up. It is also possible the
rationale is that since you need to slow the rate of advance, so you need to
extend the anneal soak.
However,
if this is the rationale, it is rarely followed through on the anneal cool in the detailed schedules in these instances. Generally, the cool on extended soaks is the
same as on the first anneal, but extending the anneal should apply to the
cool too, according to this kind of rationale.
Facts
At normal
kilnforming temperatures, the anneal for the determined thickness (allowing an adjustment of actual thickness for tack fused pieces) is suitable even for multiple
firings.
Once you go up into the
temperatures for melts, there is reason for more caution. There is the risk
that the high temperatures – especially for hot coloured opals – may induce a
little incompatibility. A longer soak
for these at a lower temperature may be considered desirable.
Even so, this does not need to be extended at each subsequent firing.
You are annealing at
each firing for the thickness – actual or calculated – of the piece, not for
the number of firings.
Further information is available in the ebook: Low Temperature Kiln Forming.
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