Stephen Sell on wed 1 oct 97
Fellow Clayart participants,
I'm trying a glaze reciepe I found in the book "Warren Mackenzie - An
american potter"... It's a ^8-10 glaze with the following proportions:
White
-----------------------------
Custer Feldspar 7.5
EPK 5
Silica 5
Dolomite 8
Zirconium Silicate 0.8%
Two questions: 1) Is the Zirconium Silicate proportion "0.8%" derived from
the total weight used to mix the batch of glaze? 2) The amount of Zirconium
Silicate (0.8%) seems small in relationship to the rest of the parts to
adequetly act as an opacifer, can this be correct? Oh yeah, one more question
- can superpax be used as a direct substitute?
All responses would be appreciated.
Getting ready to fire my castable caternary arch kiln in Pittsburgh on a
chilly fall day as the leaves begin to turn.
Stephen Sell / odaat2day@aol.com
Ron Roy on fri 3 oct 97
Hi Stephen,
Here is the glaze the way I think it should be - I think the .08 Zirconium
is a misprint - there would be no point in putting that little bit in. 8.0
would be a much more appropriate amount.
This glaze is unbalanced - way over in MgO and low in silica for a cone 8
to 10 glaze. I suspect it is at least a matte semi-matte if not a full
matte. With the Zircopax (super pax will work fine) the expansion looks
good unless your body has more than a little cristobalite. Matte glazes are
hard to predict the fit of - testing this glaze fired on your body is the
only way to find out for sure. First step is to freeze it for 24 hours and
check the fit. If it will survive another freezing and a dip in boiling
water you can feel safe.
Custer - 30.0
EPK - 19.0
Silica - 20.0
Dolomite - 31.0
Super or Zircopax - 8.0
Total 108.0
The following (a variation on the above but NOT the same) would be a more
cleanable and durable liner glaze - the expansion would be suitable for
some stoneware clays if there is not too much cristobalite present. The
best way to make sure you are not making exploding mugs would be: Glaze
just the inside of a cylinder or mug (put the glaze on a little thicker
than normal) - freeze it over night and pour boiling water into it while
it's still frozen - if it doesn't crack you are laughing. Do it in the sink
- that way if it cracks you won't burn yourself.
RR Magnesia white liner. (untested as of Oct/97)
Custer - 38.0
EPK - 10.0
Silica - 28.0
Dolomite - 20.0
Whiting - 4.0
Super or Zircopax - 8.0
Total 108.0
>----------------------------Original message----------------------------
>Fellow Clayart participants,
>I'm trying a glaze reciepe I found in the book "Warren Mackenzie - An
>american potter"... It's a ^8-10 glaze with the following proportions:
>
>White
>-----------------------------
>Custer Feldspar 7.5
>EPK 5
>Silica 5
>Dolomite 8
>Zirconium Silicate 0.8%
>
>Two questions: 1) Is the Zirconium Silicate proportion "0.8%" derived from
>the total weight used to mix the batch of glaze? 2) The amount of Zirconium
>Silicate (0.8%) seems small in relationship to the rest of the parts to
>adequetly act as an opacifer, can this be correct? Oh yeah, one more question
>- can superpax be used as a direct substitute?
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
Stephen Sell on tue 7 oct 97
Clayart,
I wanted to thank the many of you that responded to my question about
the MacKenzie White. Too many responses to reply individually. As usual,
I post these questions after I've mixed up the glaze and the pots are
being loaded in the kiln... Anyway, the results: Not really white
with a single dip but makes a great liner glaze, kinda of a glossy oatmeal
with
plenty of iron specks (standards #119), I havn't done the freeze / boiling
water test yet but visually I see no crazing. A double dip produces more of a
white with noticeable crazing.
In mud,
Stephen Sell / odaat2day@aol.com
Content in Pittsburgh after my first salt firing thinking I'll throw another
10lbs in next time.
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