Donald G. Goldsobel on mon 5 jul 99
This question is addressed to knowledgable glaze makers. I have created a
large pot that I want to single fire due to its size. I want to convert a
glaze known as G Matt 3 to single fire. The recipe follows. May I have your
suggestions. I intend to do this one time and do not want to reinvent the
wheel.
TIA Donald Goldsobel, in the San Fernando Valley where my fountain awaits
the "big" pot to finish the installation
G-Matt 3
Feldspar 50.0
Whiting 8.5
Zinc Oxide 7.7
Barium Carb 20.6
Ball Clay 9.4
Rutile 3.8
The last time I mixed this I used Kingman spar and OM#4 ball
Malone & Dean McRaine on tue 6 jul 99
Donald: I'm a seat-of-the-pants glazer but I've single fired for a long
time. I wouldn't change a thing in your glaze. The ball clay is the thing
that makes it work and you've got plenty. I'd be very surprised if you had
any problems as regards the glaze-body fit and firing. It depends in part
on your clay body. You might want to test a smaller piece first, as a
confidence builder. Just take a bone dry piece and dunk it in your glaze
or spray it. Most of the flaws that I've encountered show up by the time
the glaze is dry on the pot. I will say that starting your raw glazing
learning curve on a big and important piece is gutsy. My learning has been
trial and error and most of my errors came in the beginning.
G-Matt 3
Feldspar 50.0
Whiting 8.5
Zinc Oxide 7.7
Barium Carb 20.6
Ball Clay 9.4
Rutile 3.8
If you really want some insurance, add 1-2% bentonite. It solves a variety
of problems. I've rarely had to make any modifications to a glaze for use
on greenware. I glaze my pots bone dry and there is only a slight
difference in size or porosity-absorbancy between bone dry ware and bisque
ware. This size similarity is well illustrated in Fournier's Illustrated
Dictionary of Pottery under 'Shrinkage of Clay'. The shrinkage concerns
that are prevalent in raw glazing literature usually are based on
leather-hard glazing which I think is generally more problematic in several
ways. How you apply the glaze is an important consideration especially if
your clay body is very open. Spraying is safest. Avoid glazing inner and
outer surfaces at the same time.
Good luck
Dean
Mike Bailey on thu 8 jul 99
Dear Donald,
At a first glance I'd have thought that the rather low clay content
would rule this out as a raw glaze. However, there's a marvellous
material with the generic name CMC = Carboxymethylcellulose (or a
spelling similar to this). It's a long chained polymer derived from wood
pulp. Various grades are available and in the U.K. we use one made
especially for the ceramics industry, called Finnfix. It's what is added
to make the commercial brush-on glazes. The great thing about it is that
any glaze, yes, any glaze, can be made to work raw by adding between 2 -
4% of CMC..
The downsides, aren't there always!, is that:
1. The CMC is organic and gets attacked by bacteria. For some reason the
smell is atrocious. (Presumably the species of bacteria has a metabolism
that breaks the 'food' down leaving an unpleasant odour - just like some
people I know now that I come to think about it) This is not a problem
if you use the glaze within a few weeks. Otherwise a bactericide has to
be added.
2. The CMC can't be sieved through an 80 mesh sieve - which creates the
problem - how do you get it into the glaze? We get round this by making
the slop glaze to the normal dipping thickness, and sieving through an
80's sieve. The CMC is then added, allowed to swell up overnight, and
then whisked in using a glaze stirrer.
3. You've got to brush on several coats - which takes much longer than
the dipping or spraying.
Cheers,
Mike.
In message , Donald G. Goldsobel writes
>----------------------------Original message----------------------------
>This question is addressed to knowledgable glaze makers. I have created a
>large pot that I want to single fire due to its size. I want to convert a
>glaze known as G Matt 3 to single fire. The recipe follows. May I have your
>suggestions. I intend to do this one time and do not want to reinvent the
>wheel.
>
>TIA Donald Goldsobel, in the San Fernando Valley where my fountain awaits
>the "big" pot to finish the installation
>
>G-Matt 3
>
>Feldspar 50.0
>Whiting 8.5
>Zinc Oxide 7.7
>Barium Carb 20.6
>Ball Clay 9.4
>
>Rutile 3.8
>
>The last time I mixed this I used Kingman spar and OM#4 ball
>
--
Mike Bailey
Linda Blossom on fri 9 jul 99
I wanted to respond to some of the points made in this post about converting
glazes to single fire. I used to CMC but today use Veegum. I don't have
any problem with aging and smell and also no problem putting it through a
sieve. However, when I used cmc I didn't have these problems either. I
brush, spray, and dip glazes. Veegum does thicken the glaze but if it is to
be sprayed I add more water. I don't use 2 to 4 percent 1/2 to 1 percent is
enough. The binder (veegum or cmc) helps the glaze cling to the post and
makes the glaze stronger. The raw clay has a film that acts like little
ball bearings which is why the binder is needed. I never bisque and have
used hundreds of glazes successfully. I've left the original post attached
below.
Linda Blossom
2366 Slaterville Rd
Ithaca, NY 14850
607-539-7912
blossom@twcny.rr.com
At a first glance I'd have thought that the rather low clay content
would rule this out as a raw glaze. However, there's a marvellous
material with the generic name CMC = Carboxymethylcellulose (or a
spelling similar to this). It's a long chained polymer derived from wood
pulp. Various grades are available and in the U.K. we use one made
especially for the ceramics industry, called Finnfix. It's what is added
to make the commercial brush-on glazes. The great thing about it is that
any glaze, yes, any glaze, can be made to work raw by adding between 2 -
4% of CMC..
The downsides, aren't there always!, is that:
1. The CMC is organic and gets attacked by bacteria. For some reason the
smell is atrocious. (Presumably the species of bacteria has a metabolism
that breaks the 'food' down leaving an unpleasant odour - just like some
people I know now that I come to think about it) This is not a problem
if you use the glaze within a few weeks. Otherwise a bactericide has to
be added.
2. The CMC can't be sieved through an 80 mesh sieve - which creates the
problem - how do you get it into the glaze? We get round this by making
the slop glaze to the normal dipping thickness, and sieving through an
80's sieve. The CMC is then added, allowed to swell up overnight, and
then whisked in using a glaze stirrer.
3. You've got to brush on several coats - which takes much longer than
the dipping or spraying.
Cheers,
Mike.
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