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Vermiculite up to what temp. can it be fired???
Posted: Thu Dec 28, 2017 2:44 am
by Havi
Hi everybody.............
Just uncovered my vermiculite board in the kiln and found a crack in it.....
I had fired mesh melt, 45 minutes at 1700. The board has a crack on it.
Is it possible that the board cracked because of the temperature?
Up to what degree can the vermiculite be fired safely???
many thanks in advance,
Havi
ps the board is 1" thick
Re: Vermiculite up to what temp. can it be fired???
Posted: Fri Dec 29, 2017 7:09 pm
by Sharol
Hi Hav,
I don’t know what maximum temperature you can take vermiculite to, but I was having some cracking problems with the vermiculite base in my vitrigraph kiln. I asked the nice folks at Bullseye about it and they suggested I prefire the shelf before using it. I was told to fire it AFAP to 860 C, hold for 30 minutes and then AFAP to room temp. It won’t help your shelf that’s already cracked, but I haven’t had any of mine crack since doing this prefire.
Hope this helps.
BTW - I use vermiculite dams/forms sometimes when combing glass. I use the same prefire schedule as above when I have new forms. I comb at various temperatures up to 913 C and the forms holdup quite well. Over time they do degrade though, become more brittle and small cracks start to form.
Sharol
Re: Vermiculite up to what temp. can it be fired???
Posted: Sat Dec 30, 2017 5:54 am
by Havi
Many thanks, Sharol for your input.
So, there is more than 10 degrees difference between our firing rate, Also I think, that the length of the stay in this temp. is important. As I said, I sat at 927C i.e. 1700F for 45 minutes. [The originally recommended time was an hour and a half, but I was scared to do that].
of all the kiln shelves I have, the vermiculite is the biggest, that's the reason I prefer working with it. I have smaller mullite ones.
Right now I put the vermiculite on top of a mullite one, just to make sure the vermiculite will not break completely, the piece is too big to be on the smaller mullite. I am hoping for the best... Will see the results only tomorrow [patience..... OMG]
Later , I shall try get a bigger mullite shelf =22" by 22" [ I have a Jen Ken 24ish], OR work on a bit smaller scale.. The thing is that one needs to consider the damming too, and it need place on the shelf. The piece will be smaller considering this too.
Again, many thanks for your input,
Havi