Pete Horridge on sun 3 jul 11
My first posting..
I have just done a firing on a new clay body that has a higher molochite=3D=
20=3D
content than the usual one I use. I am trying this new one as the previou=
=3D
s=3D20
one tended to break quite easily during the raku process.
My normal transparent crackle glaze which usually gives good wide crackle=
=3D
is=3D20
completely different on the new clay body. It is thinner Striations rathe=
=3D
r than=3D20
wide gaps between the crackle lines.
My crackle glaze is 50% Gillespie Borate/50% Nephaline Syenite. My new cl=
=3D
ay=3D20
body is Scarva clays PF520 'Ashraf Hanna', my normal clay body is Scarva=3D=
20=3D
clays Smooth textured ES20.
I realise the crackle is about how the glaze sits and performs during the=
=3D
=3D20
thermal shock/reduction activity and cannot expect it to remain the same =
=3D
on=3D20
a body that shrinks less.
The question is should I try modifying my glaze or start again in search =
=3D
of a=3D20
glaze that performs well on the new clay body? Is there anything anyone c=
=3D
an=3D20
think of that will help the glaze crackle wider on a clay body that doesn=
=3D
t=3D20
shrink as much?
Many thanks for any advice suggested.
Kind regards
Pete
paul gerhold on mon 4 jul 11
Pete,
Cool more slowly.
Paul
On Sun, Jul 3, 2011 at 12:35 PM, Pete Horridge w=
rote:
> My first posting..
>
> I have just done a firing on a new clay body that has a higher molochite
> content than the usual one I use. I am trying this new one as the previou=
s
> one tended to break quite easily during the raku process.
>
> My normal transparent crackle glaze which usually gives good wide crackle
> is
> completely different on the new clay body. It is thinner Striations rathe=
r
> than
> wide gaps between the crackle lines.
>
> My crackle glaze is 50% Gillespie Borate/50% Nephaline Syenite. My new cl=
ay
> body is Scarva clays PF520 'Ashraf Hanna', my normal clay body is Scarva
> clays Smooth textured ES20.
>
> I realise the crackle is about how the glaze sits and performs during the
> thermal shock/reduction activity and cannot expect it to remain the same =
on
> a body that shrinks less.
>
> The question is should I try modifying my glaze or start again in search =
of
> a
> glaze that performs well on the new clay body? Is there anything anyone c=
an
> think of that will help the glaze crackle wider on a clay body that doesn=
t
> shrink as much?
>
> Many thanks for any advice suggested.
>
> Kind regards
>
> Pete
>
Ron Roy on mon 4 jul 11
Hi Pete,
That glaze does have a high expansion/contraction rate - if you are
saying that the craze pattern is finer than before you need to lower
the expansion rate of your glaze - a simple answer would be to add
some silica - 5, 10 and 15% but just do 500 gram batches to make sure
it will melt enough.
You can reduce the Neph Sy by the same amount.
Glaze #1 would be 50 Gil Borate, 45 Neph Sy and 5 silica.
Glaze #3 would be 50 Gil Borate, 35 Neph Sy and 15 silica.
After you mix them up and apply them - combine equal amounts of what
is left and mix them - that will be glaze #2.
Let me know if you want to try more - and let me know what frits you have.
RR
Quoting Pete Horridge :
> My first posting..
>
> I have just done a firing on a new clay body that has a higher molochite
> content than the usual one I use. I am trying this new one as the previou=
s
> one tended to break quite easily during the raku process.
>
> My normal transparent crackle glaze which usually gives good wide crackle=
is
> completely different on the new clay body. It is thinner Striations
> rather than
> wide gaps between the crackle lines.
>
> My crackle glaze is 50% Gillespie Borate/50% Nephaline Syenite. My new cl=
ay
> body is Scarva clays PF520 'Ashraf Hanna', my normal clay body is Scarva
> clays Smooth textured ES20.
>
> I realise the crackle is about how the glaze sits and performs during the
> thermal shock/reduction activity and cannot expect it to remain the same =
on
> a body that shrinks less.
>
> The question is should I try modifying my glaze or start again in search =
of a
> glaze that performs well on the new clay body? Is there anything anyone c=
an
> think of that will help the glaze crackle wider on a clay body that doesn=
t
> shrink as much?
>
> Many thanks for any advice suggested.
>
> Kind regards
>
> Pete
>
Pete Horridge on wed 6 jul 11
I just wanted to say Thank you to the people who have replied to my post.=
=3D
=3D20
Some very good suggestions.
I will be doing the following:
- Modifying my cooling/reduction process.
- Modifying my existing glaze by adding Silica
- Trying a new glaze based on GB/Custer
I will post the results.
Best wishes
Pete
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