Carol Ross on thu 7 nov 02
I had a problem with my last firing - I'm relatively new at firing and
especially at glazing - and could use some help so that I don't repeat
whatever went wrong... hopefully.
I had a dozen hand built pieces, bisqued to ^06. I applied glaze by pouring
or brushing, 3-4 coats with thinner glazes. Knowing the clay could be wet,
I candled the electric kiln for 90 minutes at 180 degrees before beginning a
slow climb to ^6. I soaked for an hour at 2242 and then cooled at ramp 125
to 1500.
When I opened the cold kiln 2 days later, two pieces had cracked. One was a
vase that had a crack from top to bottom - no seam involved; the other a
pitcher whose slab seams had come apart at the bottom & a crack had appeared
across the bottom. Both pieces had the same glaze - weathered bronze, which
I've used before without any problem.
All I can think of is that there was still moisture in the clay & that
caused the cracking. So I should candle longer or wait to fire... Is there
another explanation that I'm overlooking? I need to get some work completed
for a consignment (YES!)...
Carol
--
Everyone has a photographic memory, some just don't have film.
-Steven Wright
Ms Noel on thu 7 nov 02
Carol, A trick I learned in the 60's is to hold a small mirror to the last
open peep hole for about 10 seconds. When the mirror no longer shows any
condensation, I do the final close and start the temps up. Haven't had
cracking in many years!
Noel
NW Georgia where the leaves are brilliant and the sky is blue (at last) and
I am out of film!
----- Original Message -----
From: "Carol Ross"
To:
Sent: Thursday, November 07, 2002 9:47 AM
Subject: Cracks from Glaze Firing?
> I had a problem with my last firing - I'm relatively new at firing and
> especially at glazing - and could use some help so that I don't repeat
> whatever went wrong... hopefully.
>
> I had a dozen hand built pieces, bisqued to ^06. I applied glaze by
pouring
> or brushing, 3-4 coats with thinner glazes. Knowing the clay could be
wet,
> I candled the electric kiln for 90 minutes at 180 degrees before beginning
a
> slow climb to ^6. I soaked for an hour at 2242 and then cooled at ramp
125
> to 1500.
>
> When I opened the cold kiln 2 days later, two pieces had cracked. One was
a
> vase that had a crack from top to bottom - no seam involved; the other a
> pitcher whose slab seams had come apart at the bottom & a crack had
appeared
> across the bottom. Both pieces had the same glaze - weathered bronze,
which
> I've used before without any problem.
>
> All I can think of is that there was still moisture in the clay & that
> caused the cracking. So I should candle longer or wait to fire... Is
there
> another explanation that I'm overlooking? I need to get some work
completed
> for a consignment (YES!)...
>
> Carol
>
> --
> Everyone has a photographic memory, some just don't have film.
> -Steven Wright
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
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>
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melpots@pclink.com.
Ababi on fri 8 nov 02
Hello Carol.
Do you have the recipe?
Was there lithium carbonate in 5-10%
I think it has too low expansion.
I know a glaze like this, they used it where I learnt,and they didn't know why some
wares cracked after firing! ( I belive they still do!)
Ababi Sharon
Glaze addict
Kibbutz Shoval Israel
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
---------- Original Message ----------
>I had a problem with my last firing - I'm relatively new at firing and
>especially at glazing - and could use some help so that I don't repeat
>whatever went wrong... hopefully.
>I had a dozen hand built pieces, bisqued to ^06. I applied glaze by pouring
>or brushing, 3-4 coats with thinner glazes. Knowing the clay could be wet,
>I candled the electric kiln for 90 minutes at 180 degrees before beginning a
>slow climb to ^6. I soaked for an hour at 2242 and then cooled at ramp 125
>to 1500.
>When I opened the cold kiln 2 days later, two pieces had cracked. One was a
>vase that had a crack from top to bottom - no seam involved; the other a
>pitcher whose slab seams had come apart at the bottom & a crack had appeared
>across the bottom. Both pieces had the same glaze - weathered bronze, which
>I've used before without any problem.
>All I can think of is that there was still moisture in the clay & that
>caused the cracking. So I should candle longer or wait to fire... Is there
>another explanation that I'm overlooking? I need to get some work completed
>for a consignment (YES!)...
>Carol
>--
>Everyone has a photographic memory, some just don't have film.
>-Steven Wright
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy on sun 10 nov 02
Hi Carol,
I need to know if the glaze - at the edge of the crack - is melted or
sharp. If its rounded (melted) then the crack happened before the glaze
melted - on the way up - if it's sharp then it's a fit problem between clay
and glaze and I need to look at the glaze recipe.
RR
>I had a problem with my last firing - I'm relatively new at firing and
>especially at glazing - and could use some help so that I don't repeat
>whatever went wrong... hopefully.
>
>I had a dozen hand built pieces, bisqued to ^06. I applied glaze by pouring
>or brushing, 3-4 coats with thinner glazes. Knowing the clay could be wet,
>I candled the electric kiln for 90 minutes at 180 degrees before beginning a
>slow climb to ^6. I soaked for an hour at 2242 and then cooled at ramp 125
>to 1500.
>
>When I opened the cold kiln 2 days later, two pieces had cracked. One was a
>vase that had a crack from top to bottom - no seam involved; the other a
>pitcher whose slab seams had come apart at the bottom & a crack had appeared
>across the bottom. Both pieces had the same glaze - weathered bronze, which
>I've used before without any problem.
>
>All I can think of is that there was still moisture in the clay & that
>caused the cracking. So I should candle longer or wait to fire... Is there
>another explanation that I'm overlooking? I need to get some work completed
>for a consignment (YES!)...
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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