iandol on tue 1 jan 02
Dear Ron,
I have had a look at this one=20
>>>Did you glaze them raw or bisque? I have noticed this before with =
some bisque pots--Shino likes to rip pots apart. If you glaze one side, =
you must wet the other--helps with expansion and contraction. If you =
glazed raw--same expansion problem, just magnified<<<
As I understand this Shino thing, the glaze depends a lot on the =
activity of water soluble materials, especially the soda. The reason to =
wet both Bisque and Green clay is to reduce the incidence of "Wicking", =
that is having the capillary forces between the porosity and the =
solution draw the salts from the glaze slop to places where they are =
unnecessary. This may change the character of the vitreous phase in the =
clay and upset the CoE values.
Does that make sense?
Best regards, Ivor Lewis. Redhill, South Australia=20
Ron Roy on fri 4 jan 02
Hi Ivor,
I have had a fair amount of experience with shino glazes - more impotantly
I know potters who use them almost exclusivly - Malcome Davis to name one -
who uses a glaze with nearly 20% soda ash in it.
There is no way to stop the wicking of soluble salts as glaze dries -
either in raw glazed or bisque glazed pots. You can direct those solubles
somewhat but they always comes to the surface with the water and stay
there.
Many raw materials - Tuckers tests raw clays as they arrive - show salts on
the surface after bisque or higher temperature firing - sometimes more -
some times hardly at all.
Anyway I have no reason to think - in this case - soda ash - is a cause of
the pots dunting.
I have written to Tony trying to get more information - perhaps we are
dealing with lithium - perhaps a very low expansion glaze combined with a
high rate of cristobalite production in the body.
Anyway I am trying to be helpful - we will see.
RR
>I have had a look at this one
>
>>>>Did you glaze them raw or bisque? I have noticed this before with some
>>>>bisque pots--Shino likes to rip pots apart. If you glaze one side, you
>>>>must wet the other--helps with expansion and contraction. If you glazed
>>>>raw--same expansion problem, just magnified<<<
>
>As I understand this Shino thing, the glaze depends a lot on the activity
>of water soluble materials, especially the soda. The reason to wet both
>Bisque and Green clay is to reduce the incidence of "Wicking", that is
>having the capillary forces between the porosity and the solution draw the
>salts from the glaze slop to places where they are unnecessary. This may
>change the character of the vitreous phase in the clay and upset the CoE
>values.
>
>Does that make sense?
>
>Best regards, Ivor Lewis. Redhill, South Australia
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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