amy parker on wed 11 oct 00
I've been communicating with Will Edwards off line about this, and wanted
to post the results of my testing, since he has posted his. I had some test
cups already made up with a similiar mixture. My proportions, in the
quantities Will used, were 1000 PV 1000 GB and 100 zircopax. Will's used
300 zircopax.
I left standard 5% household vinegar in my test cups over night, and had no
leakage, and no visual changes to the glaze colorants. I additionally
tested a coblat blue version by sitting it on a lemon wedge overnight, with
no changes noticed. The colorants for the three batches I tested were blue
- 3% Co oxide, green - 2% Cu carb & 1% RIO, and tan 5% RIO & 2% rutile.
All of these formed glossy uncrazed glaze surfaces on Highwater's P5 and
RedStone clays fired to ^6 ox. The tests remain uncrazed 6 months after
firing.
Obviously Will's mileage has varied greatly from mine. The zircopax, perhaps?
I'm not going to pursue this glaze because it uses the dearly departed GB.
Any ideas on using PV besides with GB?
Amy
Amy Parker
Lithonia, GA
John Hesselberth on thu 12 oct 00
amy parker wrote:
>I've been communicating with Will Edwards off line about this, and wanted
>to post the results of my testing, since he has posted his. I had some test
>cups already made up with a similiar mixture. My proportions, in the
>quantities Will used, were 1000 PV 1000 GB and 100 zircopax. Will's used
>300 zircopax.
>
>I left standard 5% household vinegar in my test cups over night, and had no
>leakage, and no visual changes to the glaze colorants. I additionally
>tested a coblat blue version by sitting it on a lemon wedge overnight, with
>no changes noticed. The colorants for the three batches I tested were blue
>- 3% Co oxide, green - 2% Cu carb & 1% RIO, and tan 5% RIO & 2% rutile.
>
>All of these formed glossy uncrazed glaze surfaces on Highwater's P5 and
>RedStone clays fired to ^6 ox. The tests remain uncrazed 6 months after
>firing.
>
>Obviously Will's mileage has varied greatly from mine. The zircopax, perhaps?
>I'm not going to pursue this glaze because it uses the dearly departed GB.
>Any ideas on using PV besides with GB?
Hi Amy,
With only 2% copper or 3% cobalt you might barely sneak by with this
glaze, but I doubt it if you really tested it thoroughly. Looking for
color change after overnight testing with vinegar is difficult in a cup.
I do my vinegar testing on a flat surface and submerge half of it. Then
I can get it in bright light and look for both color change and surface
sheen change. I'd bet there was at least a surface sheen change if you
could get it in the right light to see it. With this recipe's low silica
(1.9) and low alumina (.15-.16) there is no way it would hold much
copper. Will's results were probably further hurt by his high Zircopax
level (the recipe in Will's post showed 15% Zircopax if you calculate it
in the traditional way). Basically, this is not a recipe (your version or
his) that I would want to use for functional work at any temperature.
John
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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