hal mc whinnie on sun 1 oct 00
hal's blue black gloss
cone 6
oxidation or reduction
albany slip 38
cryuolite 5
wollasstoneite 19
neph syn 14
ball clay 23
for color add
chrome oxide .25%
cobalt oxide .75
red iron 2.00
HAL'S GREEN BLACK
CONE 6
frit 25 27
gertsley borate 15
spodumene 40
kaolinn 18
add
tin oxide 6.8
copper carb 4.8
this is a shiny gree to black goaze with gray metaloic areas.
John Hesselberth on mon 9 oct 00
hal mc whinnie wrote:
>HAL'S GREEN BLACK
>CONE 6
>frit 25 27
>gertsley borate 15
>spodumene 40
>kaolinn 18
>add
>tin oxide 6.8
>copper carb 4.8
>
>this is a shiny gree to black goaze with gray metaloic areas.
Hi Hal and everyone,
This glaze intrigued me because it has a very unusual composition. It
has very high alumina (>0.7), a lot of lithium (0.28), more than a normal
amount of boron (0.5+), a good normal level of silica (2.9+) and a high
level of copper. I tried it (fired it to a large cone 6 tip touching)
and found it to be a very beautiful glossy, varigated green/black glaze
BUT it is VERY UNSTABLE. If clearly fails the vinegar test in about 4
hours. It is so unstable I doubt I will bother to have it leach tested,
but others that do this poorly in the vinegar test have leached 50 mg/l
of copper and up. Lithium would also leach freely from this glaze.
Please do not put this glaze on functional ware.
I would speculate that the high alumina is the main problem; however it
could also be the lithium or the boron.
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, perhaps, still necessary to say that the very best glazes cannot
conceal badly shaped pots..." David Green, Pottery Glazes
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