Cindy Strnad on mon 17 dec 01
Dear Gail,
Calcined materials will weigh less than
non-calcined. Calcined clays will have lost their
plasticity (sometimes an advantage, sometimes
not). The main difference for the Cornwall Stone,
I would expect, would be the weight difference.
Obviously there wasn't enough of a difference for
you to notice any alteration in your glaze. I
don't know what the LOI (loss on ignition--the
weight of volatiles such as water which will burn
off during firing) is for Cornwall Stone, but this
is the number you would use to calculate the
weight difference.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
Gail Dapogny on mon 17 dec 01
I keep meaning to ask about something. A friend and I often get together
and share mixing a glaze that webeach use a lot. The glaze (I'm
embarrassed to say I don't have the formula here at home) contains a
combination of custer spar, Cornwall stone, Zinc oxide, kaolin, neph sy,
and. whiting...I think that's all. Anyway, the Cornwall stone is a pain in
the butt: rather old and full of hard lumps. Although it can be broken
down by a coffee grinder, we took a chance and substituted calcined
Cornwall stone. Neither of us noticed any difference in the final outcome
of the glaze.
Were we just lucky or can that ingredient be substituted in most any glaze?
We'd like to know something about such a substitution before Cornwall comes
up for reordering sometime in the future Anyone know?
---gail
.
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
Ron Roy on sun 23 dec 01
Hi Gail,
The LOI for Cornwall Stone is about 1.5 - not something you need to take
into account when subbing raw for calcined although it may stiffen a glaze
a bit depending on what end temperature for the glaze.
A much more important factor with Cornwall Stone is the number of
variations it comes in.
See "Out of the Earth and Into the Fire" for the details on the different
analysis.
RR
>I keep meaning to ask about something. A friend and I often get together
>and share mixing a glaze that webeach use a lot. The glaze (I'm
>embarrassed to say I don't have the formula here at home) contains a
>combination of custer spar, Cornwall stone, Zinc oxide, kaolin, neph sy,
>and. whiting...I think that's all. Anyway, the Cornwall stone is a pain in
>the butt: rather old and full of hard lumps. Although it can be broken
>down by a coffee grinder, we took a chance and substituted calcined
>Cornwall stone. Neither of us noticed any difference in the final outcome
>of the glaze.
>Were we just lucky or can that ingredient be substituted in most any glaze?
>We'd like to know something about such a substitution before Cornwall comes
>up for reordering sometime in the future Anyone know?
>---gail
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
=?iso-8859-1?q?Lina=20Pardo?= on wed 1 sep 04
Hi all,
The question on zinc oxide made me want to ask about calcining in general. Should I use a different temperature for each substance, or just any low temperature gets it for all stuff?
As I understand it, calcining raw substances simply takes away the chemically combined water, and so it should work with one temperature for all. (A very different thing from fritting, of course).
Besides, I have "calcined" zinc oxide, and kaolin. What else benefits from the process and in which way?
Thanks,
Lina
Ilene Mahler wrote:
shouldn't bisque over 1000 degrees thats all it takes..Ilene in Conn. been
there done all of the wrong stuff
----- Original Message -----
From: "Maid O'Mud"
To:
Sent: Tuesday, August 31, 2004 7:29 PM
Subject: Zinc Ox
Hi all:
I've read many times on clayart that if/when my zinc gets lumpy, simply
calcine. So, yesterday I included a bisque bowl with 1 kg of lumpy zinc in
my bisque firing to my usual ^04.
Today, I have warm, lumpy zinc ox. Can anyone tell me what I did wrong?
Many TIA
Sam Cuttell
Maid O'Mud Pottery
RR 1
Melbourne, Ontario
N0L 1T0
CANADA
"First, the clay told me what to do.
Then, I told the clay what to do.
Now, we co-operate."
sam 1994
http://www.ody.ca/~scuttell/
scuttell@ody.ca
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______________________________________________________________________________
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