Tish Cook on sun 8 nov 98
Hi Joan, I calculate the shrinkage by multiplying the desired length by
12% or 13% and adding that to the desired length, or you can multiply by
1.12 x 4 and come up with 4.48(for example) that is the length that
your lid needs to be when it comes off the wheel. All clays are
different (as are people) so you may need to do some tests for your clay
body. This is the shrinkage rate for ^10-^11 I don't know about cones
below that
When making lids it is really important to 1) Do your tops and bottoms
an the same time and 2) make sure the thickness of each lip is sort of
equal so that the shrinkage will be the same.3) Don't make them too thin
as they can easily warp. 4) Be sure to compress the lid by going back to
the center a few times to take out the stress on the bottom so that if
you are lucky it won't S crack it still however does unfortunatelythis
should be before the lip is formed. These are good rules for platters
too. I find platters need to be just the right thickness, I think
thinner rather that thicker. Each clay body is different so you need to
experiment with it, but don't give up!!
I was going to reply to the compression person so here it is in one
message. My time is limited as I am on solar power and we have a rain
coming tomorrow so I need to conserve. Bye for now, Tish
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