[Natania Hume]

I recently got a used electric kiln which I've been glaze firing to cone 5/6. The person who had it previously only fired low fire. I am noticing that the shelves are warping and i plan to wash the other sides and turn them over each time I fire from now on. My question is: are the shelves perhaps not rated to go to mid range? Should I eventually get new shelves? The kiln I fire where I teach has very old shelves that aren't warped at all...are they made for higher temps.?
Thanks!

[clayshapes]

I can't help with the warping question, but do know that you shouldn't use a kiln washed shelf upside down -- kiln wash could flake off and fall onto your glazed work and ruin it!

[OffCenter]

clayshapes, on 12 February 2013 - 08:49 AM, said:

I can't help with the warping question, but do know that you shouldn't use a kiln washed shelf upside down -- kiln wash could flake off and fall onto your glazed work and ruin it!

just grind off ALL the kiln wash before turning it over. It shouldn't be all that hard to do.

Jim

[justanassembler]

Natania Hume, on 12 February 2013 - 05:23 AM, said:

I recently got a used electric kiln which I've been glaze firing to cone 5/6. The person who had it previously only fired low fire. I am noticing that the shelves are warping and i plan to wash the other sides and turn them over each time I fire from now on. My question is: are the shelves perhaps not rated to go to mid range? Should I eventually get new shelves? The kiln I fire where I teach has very old shelves that aren't warped at all...are they made for higher temps.?
Thanks!

If they are half inch "clay" (corderite/alumina/some variation thereof) they really dont last at cone 6. You have to use a thicker shelf or a thin SiC shelf, if you can justify the cost.

[neilestrick]

I've heard nothing but good things about hollow core shelves- CoreLite. Light and strong, and no more expensive than standard cordierite shelves. I got a few 14x28 recently, and they've held up well so far.

[justanassembler]

neilestrick, on 12 February 2013 - 05:46 PM, said:

I've heard nothing but good things about hollow core shelves- CoreLite. Light and strong, and no more expensive than standard cordierite shelves. I got a few 14x28 recently, and they've held up well so far.

I knew someone recently who got a bad batch of those Corelite shelves, they were the largest they make for a round top-loader. Every single one cracked nicely down the middle--I saw her stack and posting--so did Resco the mfr). Resco insisted that it wasn't a manufacturing issue, but they were also completely happy to refund her $$$. I have encountered other folks with similar issues (but only with the very largest of shelves) and a tech @ Resco spoke to acknowledged that at one point they had issues with the extrusions being prone to cracking due to a an issue with either the die or the method by which they were cutting them, I forget. Either way he said it was resolved, but I sort of wonder.

[neilestrick]

justanassembler, on 12 February 2013 - 08:49 PM, said:

neilestrick, on 12 February 2013 - 05:46 PM, said:

I've heard nothing but good things about hollow core shelves- CoreLite. Light and strong, and no more expensive than standard cordierite shelves. I got a few 14x28 recently, and they've held up well so far.

I knew someone recently who got a bad batch of those Corelite shelves, they were the largest they make for a round top-loader. Every single one cracked nicely down the middle--I saw her stack and posting--so did Resco the mfr). Resco insisted that it wasn't a manufacturing issue, but they were also completely happy to refund her $$. I have encountered other folks with similar issues (but only with the very largest of shelves) and a tech @ Resco spoke to acknowledged that at one point they had issues with the extrusions being prone to cracking due to a an issue with either the die or the method by which they were cutting them, I forget. Either way he said it was resolved, but I sort of wonder.

Interesting. Hopefully it truly is worked out. I tend to give them the benefit of the doubt, because if they didn't fix it word would get out quickly if the problem persisted. They HAVE to fix it to stay in business. The folks at Lill Street have been using them in their gas kilns for the last few years and they still haven't warped. Seems like every brand goes through some issues at some point. Thorley's went bad when Laguna first bought them out, but they got it figured out.

[potterbeth]

Highwater Clay, in North Carolina, sells 3/4" High Alumina shelves...they're the best I've found for cone 5-6 electric firing.