Gaynor Reeve on sun 9 jun 02
Can any one tell me, is it possible to fire slab pieces 35cm x 45cm on =
two shelves, closely put together. Or should I be firing them on one =
shelf. I had a piece that cracked after it's third firing, but I'm not =
sure if it was due to being placed on the two shelves or not. Is this a =
definite no..no.....
Many thanks
Gaynor
gaynor.reeve@virgin.net
Jeff Tsai on mon 10 jun 02
Hi Gaynor,
I wouldn't say that it is a definite no no. Very little in this world is
definite if you want to look at it that way.
It's not the fact that you lay the slab over two shelves that is probably
increasing the chance of cracks. Laying it over two shelves, even if by feel
and by look they seem even with each other, may cause slight warping of the
slab. Often this warping isn't very noticable, and doesn't affect the work
unless you really need something specific.
Laying a big slab of clay over a kiln shelf will cause cracks because one
side is against a surface that drops in temperature rapidly (exposed to air)
and the other is laying across a surface that retains heat as it cools (the
kiln shelf). The temperature stress on the clay will create a crack more
easily.
Something as minor as using a loose bed of coarse grog under the slab
between
the kiln shelf and the slab can help reduce the chance of cracking, since it
opens up the bottom of the slab to a little air.
-jeff
Snail Scott on mon 10 jun 02
At 04:13 PM 6/9/02 +0100, you wrote:
>...is it possible to fire slab pieces...on two shelves...Or should I be
firing them on one shelf...I had a piece that cracked...
The thicker the slab, the more resistant it will be to
the effect of bridging the crack between two shelves.
Also, be sure your shelves are dead level with one
another, with no 'ridge' /\ or 'valley' \/, or any
change in level. If they're not quite perfect, use
kiln putty on top of the posts to lift up the low
side(s), or put a thin bed of sand on the shelves
and level it with a straightedge. You can also fill
the shelf gap with kiln putty, rather like grouting
tile.
If you use sand to level the shelves, don't put any
glazed stuff underneath!
-Snail
Gaynor Reeve on tue 11 jun 02
Thank you for your reply..
I've not heard of kiln putty before, but, together with the sand, that
should do the trick...
Thanks again,
Gaynor
----- Original Message -----
From: "Snail Scott"
To:
Sent: Monday, June 10, 2002 5:40 PM
Subject: Re: Cracked slab
> At 04:13 PM 6/9/02 +0100, you wrote:
> >...is it possible to fire slab pieces...on two shelves...Or should I be
> firing them on one shelf...I had a piece that cracked...
>
>
> The thicker the slab, the more resistant it will be to
> the effect of bridging the crack between two shelves.
> Also, be sure your shelves are dead level with one
> another, with no 'ridge' /\ or 'valley' \/, or any
> change in level. If they're not quite perfect, use
> kiln putty on top of the posts to lift up the low
> side(s), or put a thin bed of sand on the shelves
> and level it with a straightedge. You can also fill
> the shelf gap with kiln putty, rather like grouting
> tile.
>
> If you use sand to level the shelves, don't put any
> glazed stuff underneath!
>
> -Snail
>
>
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Snail Scott on wed 12 jun 02
At 11:14 AM 6/12/02 -0400, you wrote:
>What is "kiln putty"?
Kiln putty is thick kilnwash. I generally use
the thick glops that build up on the side of my
kilnwash can. You can make it from scratch, too,
if your own kilnwash container is too tidy and
well maintained to have glops! ;)
For leveling shelves, it should be moldable with
fingers, like clay, and stiff enough not to
flatten into nothingness under the weight of the
shelves and work. Just put a pat of it on top of
the kiln post, then put the shelf in place and
press until it's level. Give it a few moments
to firm up, then continue loading.
-Snail
Kay Howard on wed 12 jun 02
What is "kiln putty"? And while I'm asking, what is "magic water"? =
Thanks! Kay
Kay Howard
capclay@modempool.com
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