Mike Bailey on sat 7 aug 99
Hi all,
I've noticed that the usual recommendation given by Clayart contributors
of a test for crazing is:
Put the piece in the freezer for 24hrs and then drop in boiling water.
I was wondering if the temperature at which it is frozen makes any
difference? With the implication that the temperature difference between
the 'cold' and the 'hot' that induces the crazing could vary.
This sounds like a much easier test than the one that I've been doing
which involves going from 'hot' to 'cold'. In this method the test
pieces are heated to 130 deg. C. and dropped in cold water, inspected
for crazing, then heated to 140 deg. C. and dropped in cold water etc...
through 150 deg. C and then 160 deg. C.
The problem with this method is repeatability / standardisation. The
advantage, though, is that it gives an idea of the amount of time that
will elapse before crazing starts. An approximate interpretation is that
if it crazes at:
The 130 deg. C drop it would only last a few weeks anyway.
The 140 deg. C drop = crazing within 6 months
The 150 deg. C drop = crazing within a year
The 160 deg. C drop = crazing within a few years.
If it survives the 160 deg. C. drop into cold water without crazing then
it will be craze free for more than 2 years.
At 170 deg. C. the test becomes invalid as everything crazes/cracks when
it is dropped in cold water as the shock is so great.
Any thoughts, comments?
Cheers,
Mike
--
Mike Bailey. Bath. U.K.
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