Bob Kavanagh on fri 9 may 97
Good morning
A quote to start, "I, on the other side, am argueing that all glazes will
eventually craze.", and then further on in the same post "My reasoning is
that you will always have a difference in expansion and contraction rates
because a glaze is a more of a glass than clay. So the expansion rates will
never be identical."
My problem is with the words "eventually", "rates" and "never be
identical". I assume "eventually" is not quite as long as "forever", but
maybe it is as long as it takes for mountains to get worn down into clay.
So if that's the length of time this expression means, then MAYBE glazes
will craze. But even then, they will craze if and only if at some point
the size of the rigid glaze is smaller than the size of the clay AND the
tensile stresses in the glaze involved in this situation are greater in
force than the internal strength of the glaze.
Almost all of our contraction problems are "amount" related and not "rate"
related. There can be severe situation exceptions.
Let's suppose that the coefficients of the glaze and the clay are not
"identical", when is this problematic? When the lack of identity is to the
1879th decimal point? This is problematic when the internal strength of
the glaze is surpassed. That may, in fact, never occur. In this case,
"never" means "not ever". The pot we are considering may actually
distintegrate with the passing ravages of time - like the rest of us - but
not craze - unlike some of us.
bob kavanagh (60 km west of Montreal)
| |
|
