vida vidute on tue 20 may 03
Hello,
I am having a a crazing problem of a glaze. seems that the glaze keeps cracing only with one type of clay. because I used to use one kind of clay with claer galze and it seems fine, I changed the clay and it seems to be crazing. would anybody know whay does it do that?
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mudlady@ATT.NET on wed 21 may 03
You can add increments of flint to your glaze formula: start with 5% and
increase until the crazing stops.
> Hello,
>
> I am having a a crazing problem of a glaze. seems that the glaze keeps cracing
> only with one type of clay. because I used to use one kind of clay with claer
> galze and it seems fine, I changed the clay and it seems to be crazing. would
> anybody know whay does it do that?
>
>
> ---------------------------------
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> The New Yahoo! Search - Faster. Easier. Bingo.
>
> ______________________________________________________________________________
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Lily Krakowski on wed 21 may 03
It's a basic problem. The glaze has to FIT the body just as your clothes
have to fit YOU. Think something very tight and thin. Ok. It fits your
BODY wonderfully. Then you gain ten pounds. Suddenly the tight slip tears
at the seams. You loose the ten pounds. The seams (which you now have sewn
together) do not rip. THIS IS A PRIMITIVE IMAGE. BUT NOW THAT YOU HAVE
THE BASIC IDEA:
Both glazes and clay bodies shrink in the firing. All the books will tell
you why and how. If the they do not shrink at the same rate, you will get
certain glaze defects. Crazing is the most common. It means that the body
has shrunk LESS than the glaze and (see above) on the "fatter" body the
"seams" tear. So your previous clay shrank more.
If you are mixing your own glazes the way to go is to add small amounts of
silica. Try adding 5% at a time--or do a bunch of tests and do increments
of 5% up to 15% and see what happens. That sounds like a lot, but so many
glazes are silica poor you may actually improve it.
IF YOU ARE USING A COMMERCIAL GLAZE, BUY ANOTHER. TELL YOUR SUPPLIER WHAT
THE PROBLEM IS--ESPECIALLY IF YOU GOT THE CLAY THERE--AND DO IT THAT WAY.
vida vidute writes:
> Hello,
>
> I am having a a crazing problem of a glaze. seems that the glaze keeps cracing only with one type of clay. because I used to use one kind of clay with claer galze and it seems fine, I changed the clay and it seems to be crazing. would anybody know whay does it do that?
>
>
> ---------------------------------
> Do you Yahoo!?
> The New Yahoo! Search - Faster. Easier. Bingo.
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
Ron Roy on thu 22 may 03
Just adding silica will make the glaze shiner however - the best way is to
use calculation software and increase the silica and the alumina - keeping
the alumina/silica ratio the same. It is also possible to reduce the fluxes
which have a high expansion and sub in those with a lower expansion - or do
both.
Some glazes - because of their relience on high expansion fluxed (KNaO) are
imposible to fix - same thing with those glazes (like high alumina mattes)
which need less SiO2.
The other option is to find another body that has a higher expansion - a
higher contraction on cooling.
RR
>You can add increments of flint to your glaze formula: start with 5% and
>increase until the crazing stops.
>> Hello,
>>
>> I am having a a crazing problem of a glaze. seems that the glaze keeps
>>cracing
>> only with one type of clay. because I used to use one kind of clay with
>>claer
>> galze and it seems fine, I changed the clay and it seems to be crazing. would
>> anybody know whay does it do that?
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
iandol on fri 23 may 03
Dear Ron Roy,=20
I found your about the modification of a particular glaze to improve =
gloss interesting. But just how far can you go before a specific glaze =
becomes a different glaze? Is it a one percent modification, five =
percent or greater. And what is objectively acceptable if two or three =
things are changed or alternative substitutions made?
Would it not be better teaching practice to suggest that the intended =
outcomes should be specified and then a suitable solution sought either =
by calculation or empirical testing? In other words.... Design the =
glaze.
Best regards,
Ivor Lewis
Ron Roy on fri 30 may 03
Yes Ivor you are right - simple answers to simple questions - the best
would be to use calculation software in this case but it appeared to me
this was not appropriate - and the glaze was bought.
When we try to duplicate a glaze we are sometimes disappointed because it
does not come out the same - but sometimes it is better - and we miss that.
Adding silica to a glossy glaze is often one of those win win situations -
you cure the crazing , make the glaze more durable and add body - all that
if the glaze was over fluxed to begin with.
Teaching is sometimes the art of answering the question pointing to
possible solutions.
RR
>I found your about the modification of a particular glaze to improve gloss
>interesting. But just how far can you go before a specific glaze becomes a
>different glaze? Is it a one percent modification, five percent or
>greater. And what is objectively acceptable if two or three things are
>changed or alternative substitutions made?
>
>Would it not be better teaching practice to suggest that the intended
>outcomes should be specified and then a suitable solution sought either by
>calculation or empirical testing? In other words.... Design the glaze.
>
>Best regards,
>Ivor Lewis
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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