Stephani Stephenson on sun 12 jan 03
Lily wrote
"Also: p 50, under TOXIC MATERIALS he has, to my surprise, once more,
calcium
oxide as in whiting and dolomite, magnesium oxide as in magnesite,
talc,
dolomite, zinc, titanium, sodium, and strontium."
Lily I just checked that page.. At the top of the chart it states that
the the toxic material is listed in bold type (in this case Calcium
Oxide) and that compounds containing the material as a constituent are
listed in regular type below the bold type... in this case whiting ,
dolomite..
My first guess was that the toxic form was in bold type and the less
toxic complex materials are in regular type below it.
But it is kind of difficult to figure out the exact relationships of the
groupings.. Sometimes it seems inconsistent. For example: the bold
heading Raw Lead is followed by the regular type : Lead carbonate, lead
oxide, lead sulphate and litharge. All of these are toxic as far as I
know, yet lead mono- and bi - silicate, the fritted forms of lead, are
not listed... so I don't quite get the overall purpose of this chart and
how it is organized either.
also with regard to your reference to p. 48
"whiting because of its high rate of contraction is
also good for reducing crazing in glazes."
Clark is talking about stoneware bodies immediately before that
statement and earthenware glazes immediately after so , you are right,
the statement is not very clear to the reader. From my knowledge, the
addition of whiting contributes to a somewhat lower , not higher ,
coefficient of expansion in a glaze and therefore may be useful to add
to a glaze to reduce crazing ...
I think Clark may have meant to say 'because of its LOW rate of
expansion, and therefore contraction...?????....
I have never seen whiting added to a clay body, but do see it as an
auxiliary ingredient in a number of low fire glazes.
Rhodes book does discuss additions of materials to both glazes and clay
bodies to counteract crazing, but whiting was not mentioned as an
addition to clay body.
also British materials are referred to in glaze and clay sections, so
need trnslation into American materials,but what the hey,
I'd buy it for the pictures alone
introduction to work of new (to me) and accomplished artists
and also just a different perspective on various parts of the process.
Stephani Stephenson
Lily Krakowski on sun 12 jan 03
As soon as Stephanie[?] said how great this book was, I sent for it from The
Potters'Shop. I am getting into tiles, kindof, sort of, soon.
The book is incredible. Fabulous. The kind of book you automatically go wash
your hands before picking up. MBE after Clark's name means an honorific
title--supposed Member of British Empire, not, as I had thought Master in
Business Education or something.
However there are a few things in the text that totally surprised me.
He writes (p48) that "whiting because of its high rate of contraction is
also good for reducing crazing in glazes." This remark follows one on the
use of whiting in bodies, so I wonder IS whiting added to bodies to make
them shrink more? He cannot mean IN glazes, or can he?
Also: p 50, under TOXIC MATERIALS he has, to my surprise, once more, calcium
oxide as in whiting and dolomite, magnesium oxide as in magnesite, talc,
dolomite, zinc, titanium, sodium, and strontium.
Now some time back Monona Rossol had a list of safer materials compiled by
one Lynn Barth, and dolomite, neph sy, pot. and soda spars, zinc, iron
-oxides and ilmenite were included.
Clue me in?
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
Gavin Stairs on sun 12 jan 03
I had no idea Lord Kenneth Clark was a potter or a tile afficionado.
CaCO3, whiting, chalk, limestone, marble, is about as innocuous as you can
get in the chemical world. We are surrounded by the stuff. Builds
buildings, much crushed stone is this stuff, in South Eastern Ontario it
lies beneath us everywhere. You can eat this stuff by the spoonful, and
the only likely harm will be burping and the runs, or maybe
constipation. Reacts with acids to produce calcium salts and carbon
dioxide (burp gas). In the stomach, you get gas and calcium chloride,
which is an edible salt. The chalk that underlies the south of England is
this stuff. Half the produce of England is grown in fields of chalk and
flint. Don't know why he would list it as toxic.
However, a close relative, lime, which is (or was) widely used in mortar
and plaster, is very caustic. That's burnt limestone, or quick lime, or
calcia. CaO. So maybe he naively combined those two.
Gavin
At 03:32 PM 12/01/2003 -0500, Lily Krakowski wrote:
>Also: p 50, under TOXIC MATERIALS he has, to my surprise, once more, calcium
>oxide as in whiting and dolomite, magnesium oxide as in magnesite, talc,
>dolomite, zinc, titanium, sodium, and strontium.
Snail Scott on mon 13 jan 03
At 05:04 PM 1/12/03 -0500, you wrote:
>I had no idea Lord Kenneth Clark was a potter or a tile afficionado.
I'm fairly sure that he's NOT the same Kenneth
Clark as the art historian.
-Snail
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