John Neely on tue 16 feb 99
Sitting in front of the computer on President's day, I'm catching up on
clayart digests that have been piling up for weeks in my in-box. For those
of you who read Robert Yellin's posts about shows in Japan feeling a
measure of vexation (as I do) at being unable to see them, you may take
some solace (again, as I do) in the Nezu Museum website:
http://www.nezu-muse.or.jp/
There is a link (http://www.nezu-muse.or.jp/tenrankai/tenrankai_e.html)
from the english page that shows some of the work in the current show, but
there are better photos from the Japanese page:
http://www.nezu-muse.or.jp/tenrankai/tenrankai.html
If you don't have a Japanese enabled browser, the text will look like
alphabet sup, but the thumbnails and links to larger jpegs should all work.
While I'm on the subject of things Japanese, and related to the subject of
wood ash glazes, I thought I'd offer a few recipes for synthetic ash that
my students have used with some success.
Synthetic wood ash was pretty thoroughly investigated in the early part of
this century - synthetic ash that is widely available from suppliers in
Japan is based on this research.
Masataro Ohnishi in his first book on glazes, "Tougei no Yuuyaku" gives
this recipe:
Ohnishi synthetic ash
---------------------
POTASH FELDSPAR..... 12.00
WHITING............. 63.00
MAGNESIUM CARBONATE. 5.00
BONE ASH............ 7.00
FLINT............... 3.00
KAOLIN.............. 10.00
--------
100.00
(Incidentally, Herbert Sanders quotes this recipe in "The World of Japanese
Ceramics" less one part of feldspar)
Etsuzo Katou in his book "Yuuchougou no Kihon" quotes the research of
another man, Ueda, (from 1926) with this recipe:
Ueda synthetic ash #3
---------------------
POTASH FELDSPAR..... 22.00
WHITING............. 59.00
MAGNESIUM CARBONATE. 11.00
BONE ASH............ 5.00
IRON OXIDE RED...... 2.00
MANGANESE DIOXIDE... 1.00
--------
100.00
I should point out that these would be based on well washed ash - as far as
I know ash is always washed in Japanese practice - there are enough
variables and vagaries in ceramics without throwing in a wild card like
soluble salts. Superficially, these two recipes might seem quite different,
but not nearly as different as I would guess as actual samples of ash to
be, and if you consider them as sources of alkaline earth, with a bit of
adjunct impurities (notably phosphorous) they are in fact not so far apart.
John Neely
Utah State University
John Neely on wed 17 feb 99
in a private post Vince Pitelka wrote:
>John -
>I am assuming that these recipes are cone 10?? You might want to repost
> on Clayart and specify the cone.
Hope Vince doesn't mind me replying to the whole list - some others have
written to me as well.
I guess I wasn't clear - those recipes are for *synthetic ash* - not
*synthetic ash glaze.* They serve as substitutes for ash to be used as an
ingredient in glazes at any temperature - although most effective ash
glazes do seem to be in the stoneware range. They are based on analyses of
samples of so called "common ash" (or "dobai" in Japanese.)
FWIW, I prefer the real thing, because real ash glazes are so much easier
to apply, even if the fired appearance is often quite similar. I realize
that some folks don't have the patience to do a proper job of washing ash,
or access to a sufficient quantity of ash to make worthwhile all of the
testing necessary to develop reliable ash glazes.
I'm in the midst of this subject with a glaze class right now - synopsis of
the project would show that for most wood ash, line blends between ash and
feldspar or ash and earthenware clay will yield usable glazes in the
stoneware range. Triaxial blends between ash, feldspar and some silica
source will usually yield glazes of which (given a reasonable body) even
the most fastidious proponents of craze-free stable tableware glazes will
approve. And to reveal my own biases on the subject, the next step is to
demonstrate that it is a lot faster to work from the Seger formula. (g)
If you'd like to play with this, or perhaps develop your own synthetic ash,
here are the numbers for the previously mentioned analysis by Ueda:
UEDA DOBAI
FORMULA & ANALYSIS
------------------
CaO.... .79 35.92%
MgO.... .17 5.44%
K2O.... .02 1.49%
Na2O... .01 .55%
Fe2O3.. .01 1.94%
MnO.... .01 .41%
P2O5... .02 2.14%
Al2O3.. .04 3.69%
SiO2... .29 14.09%
I'm off with a group of students to San Francisco in about ten hours, I'll
ask forgiveness in advance if I don't reply to email for a while.
John Neely
Utah State University
Logan, UT
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