Chris Campbell on tue 12 aug 97
Glaze help needed with this Cone 9 Crackle Glaze :
Ferro Frit 3269 9.9 (substituted directly for Pemco 25)
Lithium carbonate 4.6
Kaolin (calcinated) 16.0
Kaolin EPK 8.0
Silica 61.5
Bentonite 2.0
CMC 1 tsp
At Cone 9 it looks like the frosting on a glazed donut with only a few
bubbles. It has not moved or melted at all except for tiny areas where it
looks very nice.
I was told the Frit was a direct substitute for the Pemco #25 in the original
recipe but this must have been wrong. Any help Thanks Chris
Lawrence Ewing on wed 13 aug 97
Hi Chris,
The Pemco #25 repacement is OK in your glaze. You may need to check the
quantities in the original recipe. I suspect you have way too much Al2O3
and SiO2 on your glaze. An analysis shows you may have as much as three
times too much silica and twice as much clay as you should for cone 9.
If you wished to zero in on a variation on this glaze which does what you
want I would suggest a triaxial blend with one corner containing the
original glaze with the EPK and Silica removed, the second corner could
contain just EPK and the third corner just silica. You should be able to
find the glaze you want with this technique and will likely throw up some
other useful glazes as well. Alternatively some simple line blend
exploring reductions in silica and alumina would do.
Lawrence Ewing
Lecturer in Ceramics
School of Art
Otago Polytechnic
lewing@clear.net.nz
21 Slant St
Careys Bay
Dunedin
NEW ZEALAND
ph (03) 472 8801
Author of MATRIX Glaze Calculation Software for Macintosh
Richard Burkett on thu 14 aug 97
Chris,
You might try the following recalcution of your glaze (via HyperGlaze)
which should more closely match the original. This is a very odd glaze,
with extremely high amounts of lithium oxide for a cone 9 glaze, but these
seem to be balanced out by the very high silica and alumina. I'd still
advise somewhat careful handling of the raw glaze with that amount of
lithium carbonate to avoid toxicity problems on your part. How's the
durability of the glaze after firing?
Glaze name: Cone 9 Crackle Glaze
Cone: 9
Recipe: Amount
Ferro Frit 3269 10.94
Lithium carbonate 4.57
Calcined kaolin 14.65
EPK 8.94
Silica 60.90
Total: 100.00
add:
Bentonite 2.0
CMC 1 tsp
Comments:
Molecular Formula:
0.315 KNa0 1.156 Al2O3 13.646 SiO2
0.012 CaO 0.250 B2O3 0.027 TiO2
0.011 MgO 0.008 Fe2O3 0.096 F
0.646 Li2O 0.002 P2O5
0.014 ZnO
Richard
Richard Burkett - School of Art, SDSU, San Diego, CA 92182-4805
E-mail: richard.burkett@sdsu.edu <-> Voice mail: (619) 594-6201
Home Page: http://rohan.sdsu.edu/dept/rburkett/www/burkett.html
CeramicsWeb: http://apple.sdsu.edu/ceramicsweb/
HyperGlaze@aol.com & http://members.aol.com/hyperglaze/
Ron Roy on fri 15 aug 97
Hi Chris,
The two frits are quite similar and I checked out the glaze with the two
frits - they are very similar - it's the RECIPE that is wrong. Way
oversupplied with alumina and silica to melt properly.
For an almost exact result with frit 3269 instead of P25 you need some
small adjustments.
3269 - 9.9
Lthium Carb - 4.6
Calcined Kaolin 14.5
EPK - 8
Silica 58.5
Bentonite - 2.0
Total 97.5
BUT - why use all those expensive materials when it would be easy to get a
crazing glaze with common, inexpensive materials.
Well I decided to use a little frit but - here is a safe but less than
durable glaze which I am sure will craze on most bodies - if the "crackle"
is too small all you have to do is increase the silica 4% at a time to make
it bigger. The more silica you put in the more durable the glaze will be.
Frit 3134 - 5.0
G200 - 51.0 (or Custer)
Whiting - 20.0
EPK - 4.0
Silica - 20.0
Bentonite - 2.0
Total - 102.0
Ratio - 8.92
>----------------------------Original message----------------------------
>Glaze help needed with this Cone 9 Crackle Glaze :
>
>Ferro Frit 3269 9.9 (substituted directly for Pemco 25)
>Lithium carbonate 4.6
>Kaolin (calcinated) 16.0
>Kaolin EPK 8.0
>Silica 61.5
>Bentonite 2.0
>CMC 1 tsp
>
>At Cone 9 it looks like the frosting on a glazed donut with only a few
>bubbles. It has not moved or melted at all except for tiny areas where it
>looks very nice.
>I was told the Frit was a direct substitute for the Pemco #25 in the original
>recipe but this must have been wrong. Any help Thanks Chris
Ron Roy
Toronto, Canada
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
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