Chris Campbell on tue 14 nov 06
I have been trying to research this, but
I do not even know what to call it.
So, a little help please!
What do you call the quality that
determines whether a glaze coats a
clay body like a layer of glass versus
a glaze that seems to incorporate into
the clay body and be part of the vessel?
Is this a function of formulation,
application or firing method?
I want to achieve the soaking in look
but what quality am I searching for ...
what's my starting point?
Thanks in advance for any ideas.
Chris Campbell - in North Carolina
Chris Campbell Pottery LLC
9417 Koupela Drive
Raleigh NC 27615-2233
Fine Colored Porcelain since 1989
1-800-652-1008
Fax : 919-676-2062
website: www.ccpottery.com
wholesale : www.wholesalecrafts.com
Jim Murphy on tue 14 nov 06
On Tue, Nov 14, 2006, 10:02 AM, Chris Campbell wrote:
> What do you call the quality that
> determines whether a glaze coats a
> clay body like a layer of glass versus
> a glaze that seems to incorporate into
> the clay body and be part of the vessel?
Hi Chris,
"Adherence" may be the technical term you're looking for. Chapter 12 of
"Understanding Glazes" [book by Richard A. Eppler with Mimi Obstler, ISBN
1-57498-222-2] explains an understanding for developing an "interfacial
bonding zone" for proper adherence & fit [between a coating and its
substrate].
Best wishes,
Jim Murphy
Helen Bates on tue 14 nov 06
On Tue, 14 Nov 2006 11:02:51 -0500, Chris Campbell <...> wrote:
>I have been trying to research this, but
>I do not even know what to call it.
>
>So, a little help please!
>
>What do you call the quality that
>determines whether a glaze coats a
>clay body like a layer of glass versus
>a glaze that seems to incorporate into
>the clay body and be part of the vessel?
Hi Chris,
You might get some useful information using "clay-glaze interface" with or
without the quotation marks.
Cheers,
Helen in Belleville, ON
Michael Wendt on tue 14 nov 06
Chris,
The porcelain I use reacts so much
with glazes that there is sometimes
no way to see where the clay ends
and the glaze begins on a broken piece.
I attribute this to the high proportion
on fluxes present in the clay.
Notably, self glazing bodies are
termed parian porcelain:
http://museums.richmond.edu/lrgexhibitions/parian.html
I have some ideas for your assembled
colored clays that might make their
production easier.
Write me off line if you are interested.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Craig Martell on tue 14 nov 06
Chris was asking:
>What do you call the quality that
>determines whether a glaze coats a
>clay body like a layer of glass versus
>a glaze that seems to incorporate into
>the clay body and be part of the vessel?
Hello Chris:
It's called the "Coefficient of Diffusion". Yawn! Things with a high
coefficient of diffusion penetrate quickly stuff with a low coefficient
doesn't. Lithium, for example, has a high coefficient with very small,
highly charged ions that migrate easily.
>Is this a function of formulation,
>application or firing method?
Maybe all of the above. If you have access to Hamer and Hamer, there's
some info that may be helpful. Just look under "Boundary Layer" and "Buffer
Layer." If you can get ahold of a copy of Kingery's Introduction to
Ceramics there's a lot of info on Diffusion Coefficients but I wonder if
it's worth going that deep into the subject. The title of the book is
misleading. It's fairly heavyweight and a great aid to insomnia.
regards, Craig Martell Hopewell, Oregon
Ivor and Olive Lewis on wed 15 nov 06
Dear Chris Campbell.
I think the term or phenomenon you are asking about is called Body Glaze =
Interaction. On page 29 of "Glazes for the Studio Potter" Cooper and =
Royle have a photograph of the cross section of a the interface between =
glaze and clay. This appears to show a transparent layer at the top, =
given as black with large crystals growing into it from the finer =
fragmented ceramic below.
What happens will be a function of temperature, time, the solvent =
qualities of a chosen glaze and the rate at which cooling takes place. =
No doubt relative coefficients of expansion will also come into play. =
but growth of crystals from the clay into the glaze will add strength to =
the junction. Yvonne Hutchinson Cuff identifies these as Mullite =
Crystals (p 91).
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Lee Love on wed 15 nov 06
I remember when we were talking about the origins of majolica, I
came across some early faience that was more like glass than it was
ceramic, being almost all silica. Egyptian paste, or efflorescence
are self glazing techniques. More below:
"Efflorescence is a self-glazing method. The glazing materials,
soluble salts, are mixed with the raw crushed quartz and alkalis of
the body. As the water in the body evaporates, the salts cling to the
surface within thirty minutes to form a scum-like layer. In firing,
this layer melts and fuses to leave a glaze of varying thickness.
Rapid drying leads to the greatest thickness of glaze."
--
Lee in Mashiko, Japan
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
"When we all do better. We ALL do better." -Paul Wellstone
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