GORMO1@AOL.COM on thu 8 aug 02
i have a large bisque bowl that a fill to calcine in to about1200f.
jim gorman
Joyce Lee on thu 8 aug 02
Michael Wendt spoke of "calcining" ... I've looked it up many times and =
know how one calcines small amounts, but ...... shall I admit it?...... =
sure, why not.... you know so many of my other flaws ...... I have =
ALWAYS ignored that part of glaze directions. Can somebody ..... and =
will you, please... tell me what is gained by calcining for ^10 =
reduction glazes? I really would appreciate hearing your opinions.
I figure it must be more significant than I thought if Michael is going =
to begin producing calcine for sale.
Liz says so much is in the details ... I'm thinkin' that this is a =
detail I maybe shouldn't be missing.... if I'm going to be a full grown =
potter .... and I am.... going to be.......
Joyce
In the Mojave where it's been cooler for several days .... incredible in =
August ... my morning studio 4 hours have been extended to at least six =
before I really am cookin'. Feels like a gift .... big time gift.....=20
Susan Kosko on thu 8 aug 02
hi joyce -
malcolm davis says to calcine half the amount of EPK (kaolin) for shinos
because it seems to reduce crawling. so if a recipe calls for 1000
grams of EPK, i use 500 g of regular EPK and 500 g of calcined EPK. has
it made a difference? not sure, since the only times i've had crawling
on shino is on stoneware when i've gotten the glaze on too thick. so
far, shinos are the only type of glaze i use a calcined material in.
i'll append a question to your original one - are there other materials
that benefit from being calcined? and for what kinds of glazes?
suze kosko
new durham, nh, usa
Paul Herman on thu 8 aug 02
Joyce,
I calcine half of the kaolin for one of my glazes in order to reduce the
drying and firing shrinkage. The glaze contains 33.3% kaolin, which in
it's raw state will cause checking (cracking as it dries) and crawling
in the glaze fire.
Best wishes,
Hardway Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
----------
>From: Joyce Lee
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Calcine Question
>Date: Thu, Aug 8, 2002, 6:11 AM
>
> Can somebody ..... and will you, please... tell me what is gained by
> calcining for ^10 reduction glazes? I really would appreciate hearing your
> opinions.
Snail Scott on thu 8 aug 02
At 06:11 AM 8/8/02 -0700, you wrote:
>...tell me what is gained by calcining for ^10 reduction glazes?
Entire glaze batches are typically not calcined
in their entirety. Instead, only the materials
which are most affected are calcined beforehand,
then added to the recipe in place of some amount
of the non-calcined equivalent.
Glazes which contain large amounts of clay can
often have a high wet-to-dry shrinkage. This
makes them useful for glazing greenware. When
using such glazes on bisque, however, there is
often a tendency for the glaze to shrink too
much both in drying and in the early stages of
firing, when the last of the H2O is driven off.
This can cause crawling, especially in high-
viscosity or high-surface-tension glazes.
Sometimes big flakes of dry glaze even fall off
the clay, messing up the kiln shelves and leaving
behind a patchy pot.
Calcining some or all of the clay content of a
glaze can remedy this fault, since calcined clay
has already been fired once and subsequent
shrinkage will be negligible.
Using calcined clays can make it easy to adapt
engobe recipes, too. A recipe intended for green-
ware (and high shrinkage) can be modified for
application to leather-hard clay, dry clay, and
even bisque simply by increasing the percentage
of calcined clay compared with the uncalcined
amount.
Non-clay ingredients can also benefit from calcining.
Zinc is a common recipient of such treatment, and
for similar reasons: it reduces crawling in the
finished glaze.
-Snail
Ilene Mahler on thu 8 aug 02
you calcine the zinc in crystals as you go fast to temperature and if its'
calcined it will not crawl do to the fast firing..Ilene in Conn still
looking for the video on throwing square plates
----- Original Message -----
From: Joyce Lee
To:
Sent: Thursday, August 08, 2002 9:11 AM
Subject: Calcine Question
Michael Wendt spoke of "calcining" ... I've looked it up many times and know
how one calcines small amounts, but ...... shall I admit it?...... sure, why
not.... you know so many of my other flaws ...... I have ALWAYS ignored that
part of glaze directions. Can somebody ..... and will you, please... tell
me what is gained by calcining for ^10 reduction glazes? I really would
appreciate hearing your opinions.
I figure it must be more significant than I thought if Michael is going to
begin producing calcine for sale.
Liz says so much is in the details ... I'm thinkin' that this is a detail I
maybe shouldn't be missing.... if I'm going to be a full grown potter ....
and I am.... going to be.......
Joyce
In the Mojave where it's been cooler for several days .... incredible in
August ... my morning studio 4 hours have been extended to at least six
before I really am cookin'. Feels like a gift .... big time gift.....
____________________________________________________________________________
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Paul Lewing on thu 8 aug 02
on 8/8/02 5:11 AM, Joyce Lee at joycelee@IWVISP.COM wrote:
> tell me what is gained by calcining for ^10 =
> reduction glazes?
Joyce, several people have explained the benefits of calcining clay to help
prevent crawling in shinos and other glazes. All I would add to this would
be that you never want to calcine any more of the raw clay than you have to.
It's possible to replace enough of the raw clay in a recipe with calcined
that it will no longer stay in suspension.
Also someone has mentioned that it is sometimes beneficial to calcine zinc
oxide if you haven't gotten ZnO that's already been calcined. This keeps it
from clumping up in the bag, and helps prevent crawling. One thing to
remember about zinc oxide that does not apply to clay is that the zinc will
rehydrate. The clay won't. So after you calcine your zinc you need to keep
it in an airtight container.
Occasionally it is beneficial to calcine other materials, to get rid of some
impurity. I have a batch of spodumene that, when mixed with water, gets
real foamy. I have no idea what causes this, but calcining fixes that. And
there well could be materials that have blistering or pinholing problems
caused by outgassing that could benefit from calcining. Local clays with a
lot of organic materials would be a good example of this.
Paul Lewing, Seattle
Mondloch on fri 9 aug 02
> Also someone has mentioned that it is sometimes beneficial to calcine zinc
> oxide if you haven't gotten ZnO that's already been calcined. This keeps
it
> from clumping up in the bag, and helps prevent crawling. One thing to
> remember about zinc oxide that does not apply to clay is that the zinc
will
> rehydrate. The clay won't. So after you calcine your zinc you need to
keep
> it in an airtight container.
Paul,
If zinc oxide will rehydrate from atmosphere moisture after being calcined,
wouldn't it also rehydrate when it's mixed into the glaze batch? It seems
like calcining it wouldn't really help a crawling problem then.
Sylvia
---
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
HotArt@silvercreekpottery.com
http://www.silvercreekpottery.com
John Stromnes on fri 9 aug 02
Dear Joyce;
The only time I've ever used calcined clay, Kaolin or Ball Clay or common
local red earhenware clay, was to make a slip glaze adhere to a bisque
body. These high-clay glazes don't shrink right on bisque _ far too much
shrinkage _ so they usually crack and fall of my bisque as they dry, , or
worse fall off or crawl off in the firing, making a mess, or leaving
dangerously sharp edges where they've peeled back in firing still sticking
to the pot.
John Stromnes
Geoff Walker on fri 9 aug 02
Right on, Snail!
Usually calcining HALF of the clay in a high clay glaze is sufficient to
solve crawling (the most likely fault needed to be corrected), but with
zinc, it is often necessary to calcine ALL of the ZnO. Of course, this will
depend on the proportion of ZnO.
Good luck, Joyce - if you feel you have this problem in the first place.
There is not necessity to calcine anything if you don't have the crawling
problem.
Clayhugs,
Geoff.
> At 06:11 AM 8/8/02 -0700, you wrote:
> >...tell me what is gained by calcining for ^10 reduction glazes?
>
>
> Entire glaze batches are typically not calcined
> in their entirety. Instead, only the materials
> which are most affected are calcined beforehand,
> then added to the recipe in place of some amount
> of the non-calcined equivalent.
>
> Glazes which contain large amounts of clay can
> often have a high wet-to-dry shrinkage. This
> makes them useful for glazing greenware. When
> using such glazes on bisque, however, there is
> often a tendency for the glaze to shrink too
> much both in drying and in the early stages of
> firing, when the last of the H2O is driven off.
> This can cause crawling, especially in high-
> viscosity or high-surface-tension glazes.
> Sometimes big flakes of dry glaze even fall off
> the clay, messing up the kiln shelves and leaving
> behind a patchy pot.
>
> Calcining some or all of the clay content of a
> glaze can remedy this fault, since calcined clay
> has already been fired once and subsequent
> shrinkage will be negligible.
>
> Using calcined clays can make it easy to adapt
> engobe recipes, too. A recipe intended for green-
> ware (and high shrinkage) can be modified for
> application to leather-hard clay, dry clay, and
> even bisque simply by increasing the percentage
> of calcined clay compared with the uncalcined
> amount.
>
> Non-clay ingredients can also benefit from calcining.
> Zinc is a common recipient of such treatment, and
> for similar reasons: it reduces crawling in the
> finished glaze.
>
> -Snail
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