Richard Fafard/Tivoli Systems on mon 22 apr 96
I have a pin-holing problem with one glaze I call Pearl.
The glaze is cone 10 oxidation, based on Cornwall Stone and
with about 4% Rutile (and many other ingredients).
I was substituting feldspar, silica and whiting for the Cornwall
up until I got a recent load of Cornwall stone.
The Cornwall is very lumpy (compared to the feldspar) and the new
batch (with the Cornwall) pinholes MUCH more than the feldspar version.
I've soaked the kiln @ temp, underfired and overfired and slow cooled,
tried thin vs thick glaze coats... nothing seems to make a difference.
I have noticed that the outsides of pieces have fewer pinholes than
the insides. Would that indicate a draft (or lack there of) problem?
(My Bailey kiln is fairly tight). The lumpy Cornwall seems
to imply that it could be a seive problem (I'm seiving @ #50 mesh).
And the potter I share this recipe with seives @ #100 and does not see
this problem. So I will try to seive the !#@ out of this glaze and see.
The glaze is beautiful and I can't just dump it. This is the only glaze
that I'm experiencing this with (the only one with Cornwall also).
Any other ideas?
Rick -- Austin Texas.
Ron Roy on tue 23 apr 96
>----------------------------Original message----------------------------
>I have a pin-holing problem with one glaze I call Pearl.
>The glaze is cone 10 oxidation, based on Cornwall Stone and
>with about 4% Rutile (and many other ingredients).
>I was substituting feldspar, silica and whiting for the Cornwall
>up until I got a recent load of Cornwall stone.
>The Cornwall is very lumpy (compared to the feldspar) and the new
>batch (with the Cornwall) pinholes MUCH more than the feldspar version.
>I've soaked the kiln @ temp, underfired and overfired and slow cooled,
>tried thin vs thick glaze coats... nothing seems to make a difference.
>I have noticed that the outsides of pieces have fewer pinholes than
>the insides. Would that indicate a draft (or lack there of) problem?
>(My Bailey kiln is fairly tight). The lumpy Cornwall seems
>to imply that it could be a seive problem (I'm seiving @ #50 mesh).
>And the potter I share this recipe with seives @ #100 and does not see
>this problem. So I will try to seive the !#@ out of this glaze and see.
>The glaze is beautiful and I can't just dump it. This is the only glaze
>that I'm experiencing this with (the only one with Cornwall also).
>
>Any other ideas?
>Rick -- Austin Texas.
Hi Rick, What colour is theCornwall stone? I sieve all my glazes at 80 mesh
Ron Roy, Toronto, Canada
Paul Linhares on wed 24 apr 96
In article <9604221023.AA5313@notes-brahms.tivoli.com>, Richard
Fafard/Tivoli Systems
wrote:
> ----------------------------Original message----------------------------
> I have a pin-holing problem with one glaze I call Pearl.
> The glaze is cone 10 oxidation, based on Cornwall Stone and
> with about 4% Rutile (and many other ingredients).
> I was substituting feldspar, silica and whiting for the Cornwall
> up until I got a recent load of Cornwall stone.
> The Cornwall is very lumpy (compared to the feldspar) and the new
> batch (with the Cornwall) pinholes MUCH more than the feldspar version.
> I've soaked the kiln @ temp, underfired and overfired and slow cooled,
> tried thin vs thick glaze coats... nothing seems to make a difference.
> I have noticed that the outsides of pieces have fewer pinholes than
> the insides. Would that indicate a draft (or lack there of) problem?
> (My Bailey kiln is fairly tight). The lumpy Cornwall seems
> to imply that it could be a seive problem (I'm seiving @ #50 mesh).
> And the potter I share this recipe with seives @ #100 and does not see
> this problem. So I will try to seive the !#@ out of this glaze and see.
> The glaze is beautiful and I can't just dump it. This is the only glaze
> that I'm experiencing this with (the only one with Cornwall also).
>
> Any other ideas?
> Rick -- Austin Texas.
Hi Rick,
I have had my share of pinholing problems, and it seems to me that if
your kiln soak didn't work it is because it wasn't held at a high enough
temp. for long enough. If you experiment with temp. and time you should
be able to find your answer. I have also heard that rutile increases the
likelyhood of pinholing. You might try slight reductions of the amount
used to still get the desired look and lose the pinholing. The Cornwall
stone I get is very lumpy and light blue in its raw state, and I also use
80 mesh on all of my glazes it's a lot less time consuming than 100 mesh.
>From Paul in Ohio where its spring/winter/spring/winter ect.
Richard Fafard/Tivoli Systems on wed 24 apr 96
>I have a pin-holing problem with one glaze I call Pearl.
>The glaze is cone 10 oxidation, based on Cornwall Stone and
>with about 4% Rutile (and many other ingredients).
>I was substituting feldspar, silica and whiting for the Cornwall
>up until I got a recent load of Cornwall stone.
>The Cornwall is very lumpy (compared to the feldspar) and the new
>batch (with the Cornwall) pinholes MUCH more than the feldspar version.
>I've soaked the kiln @ temp, underfired and overfired and slow cooled,
>tried thin vs thick glaze coats... nothing seems to make a difference.
>I have noticed that the outsides of pieces have fewer pinholes than
>the insides. Would that indicate a draft (or lack there of) problem?
>(My Bailey kiln is fairly tight). The lumpy Cornwall seems
>to imply that it could be a seive problem (I'm seiving @ #50 mesh).
>And the potter I share this recipe with seives @ #100 and does not see
>this problem. So I will try to seive the !#@ out of this glaze and see.
>The glaze is beautiful and I can't just dump it. This is the only glaze
>that I'm experiencing this with (the only one with Cornwall also).
>Rick -- Austin Texas.
Hi Rick, What colour is theCornwall stone?
I sieve all my glazes at 80 mesh.
The Cornwall Stone is light blue. It was purchased around
12-95 from Bailey's Ceramic Supply. The clay is a cone 6-10
white stoneware. My firing schedule takes about 14 hours.
I have been reaching more like cone 11 lately, which could
point at overfiring the clay body... I do have porcelain around
but haven't tried it on that...yet.
-rick
Pelly123@aol.com on wed 24 apr 96
I use Cornish Stone in my plum recipe.....I first put it through a large
strainer that I stole from my kitchen...used to be used for pasta.....then I
put it through the 80 mesh....Sue
Ron Roy on thu 25 apr 96
Dear Rick, what you have is Purple Stone. There are 4 kinds of
Cornwal Stone, Purple, Hard White, DF (defluorinated) and Cornish stn. H&G.
So yours has flourine - the blue colour comes from Flourspar & so do the
bubbles. seems all these stones have different melting temperatures as
well.
Does the higher firing get rid of some of the pinholes? If so making the
glaze more fluid might work.
Ron Roy, Toronto, Canada
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