Ingeborg Foco on wed 14 nov 01
I am contemplating purchasing either silica carbide or nitride bonded =
shelves. (waiting for a price quote right now) =20
There is a lot of discussion in the archives but almost everything =
pertains to salt firing and wood firing.
Does anyone have any experience with either one of these types of =
shelves firing in a gas kiln to ^10 - 11 and can you tell me if you feel =
the need to use kiln wash? I have been told that a glaze drip can be =
easily chiseled off. True or false?=20
Can the damper be left open at the end of the firing without harm to the =
shelves? I will be firing in Florida so it's not like firing in =
Minnesota in the middle of January.=20
=20
Cleaning and scraping shelves then spraying them is in my opinion a =
despicable job and quite time consuming to say the least. If silicon =
carbide shelves require kiln wash then I'm not sure what their benefit =
is.=20
Thanks in advance.
Sincerely,
Ingeborg
ifoco@earthlink.net=20
vince pitelka on thu 15 nov 01
> I'll be very interested in hearing what others have to say but in my
humble
> opinion Silicon Carbide is the material of choice for reduction cone 10
> firing.
> They will be less liable to warp or crack.
Debbie -
They may be less likely to warp, but they are not less likely to crack.
High alumina shelves are much more thermal-shock resistant.
And consider the cost - $38 each for 13" by 26" by 1" high alumina, versus
$120 each for same size in 3/4" silicon carbide. Silicon carbide is a
necessity in salt firing, and the best chioce in wood firing, but not worth
the price in cone 10 reduction or oxidation firing.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
DEBBYGrant@AOL.COM on thu 15 nov 01
Dear Ingeborg,
I'll be very interested in hearing what others have to say but in my humble
opinion Silicon Carbide is the material of choice for reduction cone 10
firing.
They will be less liable to warp or crack. And yes, you probably should
coat them with something because glaze drips are not easy to chisle off
naked shelves. May I suggest coating them with ITC. Unlike kiln wash
ITC does not flake off and so you are able to turn the shelves in order to
further prevent warping.
Debby Grant in NH
Mark Mondloch on thu 15 nov 01
>I am contemplating purchasing either silica carbide or nitride bonded
shelves...
Hi Ingeborg,
I've been real happy with the nitride bonded silicon carbide shelves I
bought 3 years ago for my propane MFT car kiln ^9-10. For wash I use 2
scoops alumina hydrate to1 scoop EPK applied very thin with one of those
little foam rollers- makes very quick work of it. (The higher alumina keeps
it dusty rather then flaky.) I don't flip the shelves and there's been no
warping or cracking. I have been venting during initial cool-down stage with
no problems. New Castle Refractories Co was very pleasant to work with and
price was good- 12x24x1/2 ran about $50 each in the quantity I bought at
that time. They'll make whatever size you want. There is a set-up fee so
probably doesn't make sense for just a couple.
Only thing I'd do different is order larger size shelves- the car kiln
takes 4 12x24's on a layer. I think I'd be much happier with 24x24's and
will eventually make the change. I see no reason for such small shelves in
a car kiln and I'm always fighting to make things fit- but that was my fault
not theirs.
New Castle Refractories Co
915 Industrial St
New Castle
Pennsylvania 16102
724-654-7711
good luck,
Sylvia
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
HotArt@silvercreekpottery.com
http://www.silvercreekpottery.com
vince pitelka on thu 15 nov 01
Ingeborg wrote:
"Does anyone have any experience with either one of these types of shelves
firing in a gas kiln to ^10 - 11 and can you tell me if you feel the need to
use kiln wash? I have been told that a glaze drip can be easily chiseled
off. True or false? "
I would not recommend it, and why not use kiln wash? Those shelves should
not warp at all, so there will be no reason to turn them over. And if you
eventually do want to turn them over you can grind and wash off all the old
kiln wash and then flip them. Pots can stick very badly to unwashed silicon
carbide, and in cooling you will loose little chips of your pot all around
the base.
If you have a bad glaze run it will be a big job to grind it off the bare
silicon carbide, but it should ship off okay if you use shelf wash.
You wrote:
"Can the damper be left open at the end of the firing without harm to the
shelves? I will be firing in Florida so it's not like firing in Minnesota
in the middle of January."
I would not recommend this either. One of the primary problems with silicon
carbide shelves is that they do not have much thermal-shock resistance. In
other words, they will crack if heated or cooled abruptly and unevenly. I
learned this lesson the hard way. In my studio in Northern California I had
a 100 cubic foot car kiln and I bought 40 silicon carbide shelves - 3/4 by
14 by 28. I used to fire and cool very fast, and when I shut down my studio
almost all of those shelves had cracks from the edge or end towards the
center - classic thermal shock cracks.
You wrote:
"Cleaning and scraping shelves then spraying them is in my opinion a
despicable job and quite time consuming to say the least. If silicon
carbide shelves require kiln wash then I'm not sure what their benefit is."
If your glazes do not run, you will rarely need to clean and scrape your
shelves. In my studio in California I washed my shelves with aluminum paint
thickened with a 50/50 mix of alumina and kaolin. I applied it with a paint
roller, and I only rewashed the shelves as needed - not more than once ever
ten or fifteen firings. But I had control of my glazes and they never ran.
The shelf wash was to prevent the pots from sticking to the silicon carbide
shelf.
But I agree that there is really no advantage to silicon carbide in cone 10
reduction firing unless you can afford to get the light-weight Crystars or
Advancers. Otherwise, get high-alumina shelves. If you fire on the low
side of cone 10 you can get away with 3/4", but if you fire to full 10 or
the high side of 10 you will need 1" shelves, and they are heavy, especially
if you get 13" by 26" or 14" by 28".
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Gail Dapogny on fri 16 nov 01
Hi Ingeborg,
Our potters' guild, which has been in excistence for over 50 years, has
used several kinds of shelves. We've found it all to be a tradeoff. We
have lots of old, HEAVY silicon carbide shelves, and they are often cracked
and also warped, sometimes a lot, especially the thicker ones. The thin
ones, nitride bonded, so far are not warped, but longer ones will crack and
even occasionally break. Don't spend the money on them if you are hoping
for problem-free shelves.
The high alumina shelves are lighter (although not light), and can warp
slightly if used too much for heavy stuff without turning. They also easily
get gouges in them when there are bad glaze spills. (We are learning the
hard way to use more wasters.) But their price is right, especially when
you consider that both types will have problems.
If you never have glaze spills, I suppose that you could get by without
kiln wash, but it seems risky to me.
------Gail
>I am contemplating purchasing either silica carbide or nitride bonded
>shelves. (waiting for a price quote right now)
>Cleaning and scraping shelves then spraying them is in my opinion a
>despicable job and quite time consuming to say the least. If silicon
>carbide shelves require kiln wash then I'm not sure what their benefit is.
>Thanks in advance.
>
>Sincerely,
>
>Ingeborg
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
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