Wes Rolley on sat 21 may 05
I have read a lot of good works about glazes and the books that I have re=
ad, the workshops that I have attended, have taught me a lot. They deal e=
xtensively with questions of melt, safety, stability, color, materials. =
But none of them has presented a reasonable, systematic method of formul=
ating a glaze to have the appropriate characteristics for application.
- what makes a glaze flow smoothly and evenly?
- what makes a glaze "move"?
- what makes a glaze adhere to a (bisque, bone dry, leather hard) pot?
- how do you modify a glaze for different methods of application: dipping=
, pouring, spraying?
Is there any source that does that?=20
I have found a bit more of this type of information re: slips than I have=
found re: glazes.=20
--=20
"I find I have a great lot to learn =E2=80=93 or unlearn. I seem to know =
far too much and this knowledge obscures the really significant facts, bu=
t I am getting on." -- Charles Rennie Mackintosh
Wesley C. Rolley
17211 Quail Court
Morgan Hill, CA 95037
(408)778-3024
http://www.refpub.com/
Dave Finkelnburg on sun 22 may 05
Wes,
You ask a great question!
The short answer is you can read through the technical literature and find bits and pieces, or take your chances with Taylor and Bull, 1986, or Norton, "Fine Ceramics," or Parmelee & Harman, "Ceramic Glazes, 3rd ed." but none of them, nor all of them collectively, in my experience, really are definitive. Part of the reason is much of what you ask is proprietary information guarded by industry and some of what you ask is so situation-specific that no resource can answer all the possible questions.
The issue, of course, is WHAT do you consider to be "appropriate characteristics for application?" How are you applying the glaze and what are you applying it onto, and how thick do you want the glaze coat? Are you green glazing on leather-hard ware? Or, are you dipping soft biscuit-fired ware? Or, are you spraying hard biscuit-fired ware? Or, are you applying your glazes with a brush. Or, are you.....well, you get the idea. :-) There are a lot of possible answers to your question, and yes, it would take a book to answer all of them. In general, here are a few starters.
1. In every case, use enough "suspender" to keep the coarse, heavy" ingredients from settling. Clay is the easiest, most available suspender...IF...it works with the recipe. Clay works because it has a lot of surface area. Clay naturally flocculates in water. Really good bentonites, like veegums, are a useful clay if you can't stand much clay in the recipe because of the alumina or silica (or both) in the clay. The finer the clay the more it "hardens" the surface of the dry glaze so you can handle the ware without the glaze "dusting."
2. Single-fire glazes for application to greenware that hasn't dried yet need to mimic the shrinkage of the body--they need a lot of clay!
3. Glazes for soft bisque need to be relatively thin or the application will tend to be quite thick. Use a density of about 1.4 and avoid flocculating the glaze excessively. Soluble salts from soda ash, pearl ash, nepheline syenite or Gerstley borate, among others, tend to coagulate a glaze, which produces an effect much like flocculation.
4. Glazes for hard bisque need to be quite thick, but not lumpy. Use a density above 1.6. Use a dispersant to get good flow at high density, and, if necessary, coagulate the glaze.
5. For spraying, you can use almost anything. It may be easiest, and most successful, to use a glaze prepared as in 4.
6. For brushing...well, I don't brush much and know only that I don't understand this well enough. I'd appreciate some coaching on the subject myself!
Use the density numbers above only as a rough guide! The best glaze consistency is what works for you!
I hope this is helpful.
Good potting!
Dave Finkelnburg
Wes Rolley wrote:
I have read a lot of good works about glazes .... But none of them has presented a reasonable, systematic method of formulating a glaze to have the appropriate characteristics for application.
- what makes a glaze flow smoothly and evenly?
- what makes a glaze "move"?
- what makes a glaze adhere to a (bisque, bone dry, leather hard) pot?
- how do you modify a glaze for different methods of application: dipping, pouring, spraying?
Is there any source that does that?
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URL Krueger on sun 22 may 05
On Sunday 22 May 2005 10:37 am, Dave Finkelnburg wrote:
> The issue, of course, is WHAT do you consider to be
> "appropriate characteristics for application?" How are
> you applying the glaze and what are you applying it onto,
> and ... There are a lot of possible answers to your
> question, and yes, it would take a book to answer all of
> them.
So Dave, when's the book coming out?
Sign me up for a copy.
--
Earl K...
Bothell WA, USA
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