Carol Tripp on mon 6 nov 06
Hi,
Coming out of long term lurking to pose a question.
At the new art centre, we are using a high fired stoneware from Potclays
called White St Thomas. It's too heavily grogged to made slip out of easily
so I decided to make up slip from 'scratch'. I read through the archives and
the following recipe looked to be widely used. I made up three batches of
it.
25 potash feldspar
25 flint
25 china clay (aka kaolin)
25 ball clay
plus 7% RIO for the brown batch, 2%cobalt carb for the blue, 3% chromium
oxide for the green
I applied each to a leatherhard test pot; painted it on thick and thin,
carved through some parts, etc.
Following the bisque fire (^04), the brown and blue slip is flaking off the
pots where ever it is thick. The green seems to be ok unless you really
pick at it with a will to test its strength.
What am I doing wrong? I expect the answer is staring me in the face but I
just cannot see it.
Thanks for any ideas on what to do next.
Best regards,
Carol
Dubai, yes, still here
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Snail Scott on mon 6 nov 06
At 03:46 PM 11/6/2006 +0000, Carol wrote:
>25 potash feldspar
>25 flint
>25 china clay (aka kaolin)
>25 ball clay
>Following the bisque fire (^04), the brown and blue slip is flaking off the
>pots where ever it is thick...
>What am I doing wrong? I expect the answer is staring me in the face but I
>just cannot see it.
Although 50% clay isn't normally too much, if
your base clay is as heavily grogged as you say,
it may have an even lower-than-normal shrinkage,
making the slip still too shrinky by comparison.
Try replacing the kaolin with calcined kaolin.
You can make your own by throwing some kaolin
into an unglazed bowl and putting it through
a normal bisque fire.
-Snail
claybair on mon 6 nov 06
Hi Carol,
I make my slip with the claybody I am using (Currently ^5 B-Mix).
I'd recommend you do the same. Use a fine mesh sieve
to get rid of the grog. I usually use the thick slurry from my
reclaim or throwing water. You can add water to it if it's too thick
to sieve and decant it off the next day. I then let it sit in an open
container to
evaporate the water and thicken if necessary.
I haven't had any problems with it cracking off even when thick
as it remains a perfect fit.
Gayle Bair - in the giant Puget Sound damp box
with windy record breaking 60+ F temps with rain, rain, rain and any
place prone to flooding is or will be soon! I think the likelihood of a
drought
being declared here this year is very slim!
Bainbridge Island, WA
Tucson, AZ
http://claybair.com
-----Original Message-----
From: Carol Tripp
Sent: Monday, November 06, 2006 7:46 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Slip falls off the pot
Hi,
Coming out of long term lurking to pose a question.
At the new art centre, we are using a high fired stoneware from Potclays
called White St Thomas. It's too heavily grogged to made slip out of easily
so I decided to make up slip from 'scratch'. I read through the archives and
the following recipe looked to be widely used. I made up three batches of
it.
25 potash feldspar
25 flint
25 china clay (aka kaolin)
25 ball clay
plus 7% RIO for the brown batch, 2%cobalt carb for the blue, 3% chromium
oxide for the green
I applied each to a leatherhard test pot; painted it on thick and thin,
carved through some parts, etc.
Following the bisque fire (^04), the brown and blue slip is flaking off the
pots where ever it is thick. The green seems to be ok unless you really
pick at it with a will to test its strength.
What am I doing wrong? I expect the answer is staring me in the face but I
just cannot see it.
Thanks for any ideas on what to do next.
Best regards,
Carol
Dubai, yes, still here
_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today it's FREE!
http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
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Snail Scott on tue 7 nov 06
>At 03:46 PM 11/6/2006 +0000, Carol wrote:
>>25 potash feldspar
>>25 flint
>>25 china clay (aka kaolin)
>>25 ball clay
>>Following the bisque fire (^04), the brown and blue slip is flaking off the
>>pots where ever it is thick...
>>What am I doing wrong? I expect the answer is staring me in the face but I
>>just cannot see it.
At 11:18 AM 11/6/2006 -0600, I wrote:
>Although 50% clay isn't normally too much, if
>your base clay is as heavily grogged as you say,
>it may have an even lower-than-normal shrinkage,
>making the slip still too shrinky by comparison.
I just realized how dumb this reply was.
If this stuff went on leather-hard clay,
with 50% non-plastic ingredients, it probably
has too LOW a shrinkage, not too high. Try
reducing the flint, and maybe the feldspar
too, a bit.
-Snail
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