John Hesselberth on tue 4 may 99
As I reported to everyone a few weeks ago, I wanted to try getting a
truer black with RR #3 (Custer) by increasing the cobalt from the 1.0%
Ron recommended.
I tried 1.5 and 2.0% cobalt carbonate. The results just arrived in the
mail today and the cobalt leaching levels were below the detectable limit
of 0.05 mg/l for both. That is even lower than I got for 1.0% cobalt;
however that sample was close to the detectable limit so I conclude they
are all near or below the detectable limit within experimental
variablity. It would seem not to be possible to make a glossy black
glaze with any lower leaching propensity.
For those who missed it, here is the recipe.
Ron Roy Black #3 (Custer version) (Cone 6 oxidation)
Custer Feldspar 22
Whiting 4
Talc 5
Frit 3134 26
EPK 17
Flint 26
Add
Bentonite 2
Red Iron Oxide 9
Cobalt Carbonate 1-2 to get depth of black desired.
I'd love to see someone else test this with their ingredients, their
glaze mixing and application techniques and their kiln. Similar results
from another person would really nail this one down as one extremely fine
glaze. Any hope of that happening????? It really doesn't hurt you know
and only costs $20.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
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