Laura FREEDMAN on tue 2 feb 99
I have been making larger platters lately and have been experiencing
some problems with cracks. I am figuring it is with my drying methods,
is that correct? After trimming I put some of the items in an unused
fridge to dry out a bit. Sometimes I remove them before they are bone
dry (it takes forever in the fridge, sometimes a month or more), and I
can't stand waiting that long but I am learning patience. Sometimes I
leave them in there a few days to a week and then remove them to get to
the bone dry state(maybe this negates the slow fridge drying). This
morning I removed a large all in one bowl and platter from the kiln, it
was on the bottom of the kiln. It was in a thousand pieces but mainly
slices horizontally. What could have done this? Is it better to just
leave them in the fridge until bone dry or is there another method?
Any suggestions are welcome. Thanks.
David Hendley on wed 3 feb 99
It sounds like your platter broke during cooling, not
during drying or firing. If the 'thousand pieces' were not
stuck onto the kiln with glaze, you know the piece broke
during cooling.
Breaking during cooling indicates that the glaze and the
clay are not compatible. This sounds like an extreme
case of shivering. or a glaze that does not shirink enough
on cooling to fit the pot.
David Hendley
Maydelle, Texas
At 03:11 PM 2/2/99 EST, you wrote:
>----------------------------Original message----------------------------
>I have been making larger platters lately and have been experiencing
>some problems with cracks. I am figuring it is with my drying methods,
>is that correct? After trimming I put some of the items in an unused
>fridge to dry out a bit. Sometimes I remove them before they are bone
>dry (it takes forever in the fridge, sometimes a month or more), and I
>can't stand waiting that long but I am learning patience. Sometimes I
>leave them in there a few days to a week and then remove them to get to
>the bone dry state(maybe this negates the slow fridge drying). This
>morning I removed a large all in one bowl and platter from the kiln, it
>was on the bottom of the kiln. It was in a thousand pieces but mainly
>slices horizontally. What could have done this? Is it better to just
>leave them in the fridge until bone dry or is there another method?
>Any suggestions are welcome. Thanks.
>
Earl Brunner on wed 3 feb 99
One of the things I do with large flat peices is cover the rims with plastic
and let the middle get way ahead on the drying, then the rim seems to shrink
in to the middle, not the middle out to the rim(causing cracks). I dry them
upside down as well. I also make very sure that I compress the heck out of
it as I throw it. Corey Roth at Tom Coleman's studio came up with the idea
to punch a bunch of holes in folded up sheet plastic in a nice even pattern
then unfold the plastic and cover the platter with it. It works great
because it allows the platter to dry slow and evenly. A side problem is
that we have very hard water here in Las Vegas and as the platters dry, the
water migrates to the holes to evaporate and it seems to leave a higher
concentration of soluable salts at the holes with the end result that the
platters have a nice pattern of circles that show up after firing. They are
permenent, sort of like light salting of the clay.
Earl Brunner
Laura FREEDMAN wrote:
> ----------------------------Original message----------------------------
> I have been making larger platters lately and have been experiencing
> some problems with cracks. I am figuring it is with my drying methods,
> is that correct? After trimming I put some of the items in an unused
> fridge to dry out a bit. Sometimes I remove them before they are bone
> dry (it takes forever in the fridge, sometimes a month or more), and I
> can't stand waiting that long but I am learning patience. Sometimes I
> leave them in there a few days to a week and then remove them to get to
> the bone dry state(maybe this negates the slow fridge drying). This
> morning I removed a large all in one bowl and platter from the kiln, it
> was on the bottom of the kiln. It was in a thousand pieces but mainly
> slices horizontally. What could have done this? Is it better to just
> leave them in the fridge until bone dry or is there another method?
> Any suggestions are welcome. Thanks.
eden@sover.net on fri 5 feb 99
Hi Laura,
I am understanding from this post that you are talking about the first
firing, the bisc, not the glaze firing. If that is true then it brings to
mind an observation Ron Roy offered awhile back which is not to fire
platters in the bottom of the kiln as the kiln tends to lose heat too fast
in the lower half for that shape. This bit of wisdom seems self-evident
once you think about it......thanks once again to the miracle that is
Clayart.....
Eleanora....at this very moment firing-down a bisc in hopes of no untoward
surprises....I find that the very top as well as the bottom can cool too
quickly for platters...
At 03:11 PM 2/2/99 -0500, you wrote:
>----------------------------Original message----------------------------
>I have been making larger platters lately and have been experiencing
>some problems with cracks. I am figuring it is with my drying methods,
>is that correct? After trimming I put some of the items in an unused
>fridge to dry out a bit. Sometimes I remove them before they are bone
>dry (it takes forever in the fridge, sometimes a month or more), and I
>can't stand waiting that long but I am learning patience. Sometimes I
>leave them in there a few days to a week and then remove them to get to
>the bone dry state(maybe this negates the slow fridge drying). This
>morning I removed a large all in one bowl and platter from the kiln, it
>was on the bottom of the kiln. It was in a thousand pieces but mainly
>slices horizontally. What could have done this? Is it better to just
>leave them in the fridge until bone dry or is there another method?
>Any suggestions are welcome. Thanks.
>
Eleanora Eden 802 869-2003
Paradise Hill
Bellows Falls, VT 05101 eden@sover.net
"If I had words to make a day for you
I'd sing you a morning golden and new
I would make this day last for all time
and send you a night filled with moonshine"
-----Arthur Hoggett, in "BABE"
Laura FREEDMAN on sun 7 feb 99
Eleanora, thanks. Yes, it is a bisque firing. I have since talked to a
potter in my studio (there are 4 of us, although we are never there at the
same time) who has a lot more experience than I do and she said just about
the same thing you did. I no longer put my platters on the bottom or tippy
top. I am thinking about purchasing an Envirovent, do you think it would
help things in the kiln by a more even heating? I have no experience with it.
Laura
:
Bob Wicks on sun 7 feb 99
Hi Laura:
You never mentioned what clay you are using for your platters. I do know that
Penn Mo had that problem with a large batch of Standard clay and many
customers sent it back. I wonder if the clay has not been wedged properly.
Only you can answer that. Have you tried mixing some grog (you will have to
experiment here) to the clay body so it will breathe better and thereby
eliminate the cracks? Now I think you should try this before doing anything
else. Dust your shelf with a fine layer of silica sand or alumina hydrate.
Then place your work on top of the dusted area. This will allow the plate to
shrink without sticking to the shelf
Bob
Mimi Stadler on mon 8 feb 99
Hello Laura-
I don't think an Envirovent will even out kiln temperature. I have had one
for 10 years. There is a difference of more than a cone (close to 2) from the
bottom and middle, which are fairly close in temp, to the top, which is much
cooler.
Mimi Stadler
Tracy Wilson on mon 8 feb 99
Hi Laura,
I was having problems with large platters cracking in the bisque. And if I
stacked them... Watch out! Again I thought maybe I wasn't drying them
properly. Now, when I bisque, I put them on three little broken kiln shelf
pieces so the bottom can have warm air circulate under them. If I stack 2
or 3 platters on top, I'm sure to place the next level of kiln shelf pieces
exactly above the pieces from the platter below. My cracking problem has
disappeared. (actually I have small refractory blocks, now but kiln shelf
pieces worked before I got them)
Good Luck and maybe this will help.
Tracy
____________________________________
Tracy Wilson
Saltbox Pottery
4 Shaw Rd.
Woolwich, ME 04579
phone: 207-443-5586
fax: 207-442-8922
email: tracy@saltboxpottery.com
web: www.saltboxpottery.com
___________________________________
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