Tuesday, 22 February 2011

More wrongness.

So, I did a new batch of glaze yesterday, hoping that it would fix the peeling issue.  I know that, to fix the peeling, you need to reduce the amount of silica in the glaze - it's the opposite of crazing - and so I used a china clay which is much lower in silica.  But I kept the proportions the same - 80% LBS, 20% clay (16% china clay, 4% hyplas, plus 1% bentonite.)  I raw glazed two pots that weren't that great, so I didn't really care what happened to them.  Here they are:

Well, the quality of the glaze is really nice.  It's very clear, slightly less yellow that the last one.  I specifically want that.

But it didn't stop the pinging off of the glaze.  I did - and this might not have helped - well, the kiln was quite hot when I opened it and removed the pot.  About 150 degrees.  But I think the peeling isn't necessarily to do with that - it's the glaze needs fixing.

So today I've made some test tiles.  I did this by making some small bowls - dog bowl type bowls - which I've quartered.  The reason for doing this is because I want the tiles to be like these rims - so they're shammy'ed and the outside is ribbed, just like these pots.  I've slipped them halfway across, so half is slipped and half is just plain clay.  I have 23 tiles (one has the black slip - I want to see what it's like.)

I'm going to do tests in proportions of LBS to various clays, in 70/30, 80/20 and 90/10 tests, using AT, ESVA and china clay.  I can't guarantee that this peeling is going to happen.  So I will do two of each - one for top shelf and one for at the bottom.  The ideal would be to find a glaze that crazes, so i can then add some silica to to fix the crazing.

I've also got some borax frit, but all the glazes call for colemanite (either as it is, or in fritted form) which I don't have.  Wondering whether to abandon lead, but almost every earthenware potter I know is using it and does produce nice glazes.  Why don't they get this problem?  (I'm even using their glazes!)

Just need these tiles to dry so I can bisque them, now.  Not doing any more glaze firings until I've done the tests, I think.

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