Chaeli Sullivan on sun 18 feb 07
Can one glaze be used for the exterior of a vase (Feldspar, Borate,
Silica, Whiting & Kaolin)and then a totally different glaze (ash glaze -
plain ash, no additives) be used to coat the inside?
Will these work harmoniously with each other, or have different drying co-
expansion rates which result in breaking the vessel?
Has anyone tried this?
Thanks in advance for your answers.
Chae
Richard Walker on sun 18 feb 07
I do this fairly frequently using a liner glaze, usually clear, and then another glaze for decorative purposes on the outside. I have never had any trouble with using two different glazes assuming both had previously proved stable, ie, no crazing, pin holing, etc. Have used heavy matt glazes on the outside and gloss glazes on the inside, no problem.
Good Potting. Dick
>From: Chaeli Sullivan
>Date: 2007/02/18 Sun PM 03:22:25 CST
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Different Glaze for Pot Insides
>Can one glaze be used for the exterior of a vase (Feldspar, Borate,
>Silica, Whiting & Kaolin)and then a totally different glaze (ash glaze -
>plain ash, no additives) be used to coat the inside?
>Will these work harmoniously with each other, or have different drying co-
>expansion rates which result in breaking the vessel?
>Has anyone tried this?
>Thanks in advance for your answers.
>Chae
>
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Ron Roy on mon 19 feb 07
Hi Chae,
Depends - on the expansion contraction rate of the two glazes and the clay body.
It certainly is possible but there are combinations that you want to watch
out for.
If you have a low expanding/contracting (Expansion happens during heating
and contraction happens during cooling) glaze inside and a crazing glaze on
the outside - the inside glaze may crack the pot because the crazing glaze
makes the pot weaker. Using two low expanding glazes inside and outside on
that same clay may be OK because they "balance each other.
There are way to test your combinations - freeze the pots - if they are
still uncracked after 24 hours - pour boiling water into them (in the sink)
while they are still frozen - if they survive that they will be able to do
most of what is required in the kitchen and table.
You can get a pretty good idea about the expansion of shiny glazes using a
calculation program by the way - send me some recipes and I'll give you
some examples. Finding the expansion rate of clays is harder but it can be
done. Always remember - each clay you use will have a different
expansion/contraction rate so you have to test them all.
RR
>Can one glaze be used for the exterior of a vase (Feldspar, Borate,
>Silica, Whiting & Kaolin)and then a totally different glaze (ash glaze -
>plain ash, no additives) be used to coat the inside?
>Will these work harmoniously with each other, or have different drying co-
>expansion rates which result in breaking the vessel?
>Has anyone tried this?
>Thanks in advance for your answers.
>Chae
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Chaeli Sullivan on mon 19 feb 07
Thanks Dick.
Of the two "pots" fired; both have broken. Definite crack lines
completely circle the outside; but strangely hold liquid (figure the glaze
sealed any leakage). The first one fired on NY's Day has held oil-lamp
fuel from Jan 1 without any apparent problems!
Needless to say, I am trying to isolate the problem. Had been raw firing.
Using ash glaze on the inside; already mentioned glaze on the outside.
Thought that might be a contributing factor. Especially since, on Friday,
tried bisque firing a different piece and it survived the firing just fine!
Now i'm in a quandry, of course. If it's not the kiln (not an ideal kiln
for firing pottery); and it's not the clay content (used the same clay and
method of sculpture); how should i proceed to finish the piece?
Anyhooo, just some "outloud" thoughts. Thanks again for letting me know 2
different glaze recipes will work on the same object.
Chae
On Sun, 18 Feb 2007 19:54:57 -0600, Richard Walker
>I do this fairly frequently; have never had any trouble using two
different glazes
>Good Potting. Dick
>>From: Chaeli Sullivan
>Can one glaze be used for the exterior of a vase (Feldspar, Borate,
Silica, Whiting & Kaolin)and then a totally different glaze (ash glaze -
plain ash, no additives) be used to coat the inside?
Chris Groat on mon 19 feb 07
I took a ceramics class in college. The last pots of mine that were fired
were three larege vases (2'-3' tall), thrown fairly thin. I used a
different glaze on the inside and the outside. They looked fine when they
came out of the kiln. Within 24 hrs, each one had cracks that spiraled up
the pot. All the pots were in two pieces, wound around eachother like two
strands of double helical DNA. That being said. I almost always have a
different glaze on the inside and the outside, but in a few rare cases the
different expansion coefficients of the glaze can cause problems.
Chris
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