Wednesday, August 19, 2009

Why kiln God, WHY?!?!



This type of cracking has been happening all too often. I stack 2 dinner plates for bisque firing. The feet line up well so that there's no unsupported weight, and I never stack more than 2. The plates are totally bone dry. I ramp up the kiln slowly. So why then do I get these tragic cracks? WHY?!?!?!?!?

8 comments:

June Perry said...

Hate when that happens! Sometimes you get cracking because the bottom of the plate is not thin enough and as the plate cools, the rim cools faster than the bottom. You can try making the base thinner, or sitting the base up on a few pieces of bisqued wads, or putting notches in the foot, etc.
It may also have something to do with compression during throwing.

William Baker said...

Emily,
That's a tough crack on such a beautiful plate. I first noticed that it comes right off the point where you carved in, so I thought maybe you over stressed it there.
But June has a good point, and the crack seems to curve into where the thicker foot ring might be.
Break one open and look at it--if June's suggestion is correct you should be able to see it.

June Perry said...

PS: Sometimes, uneven drying is the problem. Covering the plate with plastic, but leaving a hole so the center of the plate, can help even out the faster drying rim.

John Britt said...

E,

I am on with what June and Will suggest. I think it is beginning where the cutting happens (at the "v"). Another antidote may be to pierce the plate with a fettling knife just below the "v" and see if that stops it. It may not work ??!! But if you were desperate. Another solution may be to cut a "u" shape to not incourage the crack???


John

Lindsay Rogers said...

Since it has happened several times... does it always come from the "v"? Just curious...

Clay Club said...

Y'all are so smart! That's why they pay you the big bucks, eh?
I'm leaning towards June's cooling theory. I busted it to see the cross section and the plate's pretty damn uniform in thickness.
This type of crack doesn't always show up at the "V" in the cut af the rim. If it were the "V," I wouldn't think it would crack so far into the plate, but I don't really know anything anyways.
Thanks so much for the input!
I can always count on you guys ;)

June Perry said...

Another thought on plate firing. If you're bisquing in an electric kiln, try to place the plates toward the top of the kiln where they won't cool down as fast.

cynthia said...

If you come this way bring a plate to look at .......