John Hesselberth on wed 5 jan 00
Here's some great news on a green, copper-containing satin mat glaze that
is very attractive. The original test work was done by Clayart member
Heidi Haugen--thanks Heidi for taking the lead on this one! She had
tested at Alfred Analytical a glaze she liked called Xavier's Warm Jade
Green (source: Cushing's Handbook). When she sent the results to me for
comment it looked so promising that I decided to test it a little more
extensively. The results from those tests are back now and this is the
best high-copper-containing glaze I have seen when it come to glaze
stability in the standard leaching test. It also happens to be a very
attractive cone 6 satin mat or semimat.
As you will see below, the results are a little scattered; however I
don't consider this to be unusual. There is a fair amount of
experimental variation both in mixing and firing glazes and in the
analytical work to measure leaching performance. The point is all of
these numbers are pretty low compared to what I have seen in other
copper-green glazes. Here are the recipe and the results--you be the
final judge.
Xavier's Warm Jade Green
Custer Feldspar 40.0
Frit 3124 9.0
Whiting 16.0
Talc 9.0
EPK 10.0
Flint 16.0
Add
Rutile 6.0
Copper Carbonate 4.0
Unity Calculations
K2O 0.134
Na2O 0.088
CaO 0.562
MgO 0.216
Al2O3 0.343
B2O3 0.055
SiO2 2.988
Heidi tested the glaze as written above. I tested it with 3, 4 and 5%
copper. I also tested for boron on the 4% sample. Here are all the
leaching results.
Heidi's test 4.0% CuCO3 4.2 mg/l Cu
John's tests 3.0% CuCO3 2.75 mg/l Cu
4.0% CuCO3 0.68 mg/l Cu, 0.04 mg/l B
5.0% CuCO3 3.07 mg/l Cu
Yes, as I noted above, there is some unexpected variability--I certainly
wouldn't expect 4% Cu to have lower leaching than 3% copper. However I
expect if I repeated these test 10 times and averaged the numbers they
would fall right into line with expectations. The boron leaching is so
low it is not worth a second thought. The exiting thing to me is that I
have tested 2 other green glazes that are very similar in appearance to
this one and one leached 15-30 mg/l Cu while the other leached about 5-15
mg/l Cu. This one is clearly the best of the lot. As I explained a few
weeks ago on Clayart, while there is no standard for copper leaching, my
personal goal is less than 10 mg/l and Monona would challenge us to
approach the water limit of 1.3 mg/l. This glaze clearly is better than
my own goal and approaches the water limit. It is, of course, far better
than the 15-30 which is the best I had seen a year ago when I started
this work. You can bet I will be testing this glaze in larger scale and
switching to it if it continues to look good.
If you are interested in examining the results from all three glazes,
they are on my web site (URL below). One is called Gray-Green mat
(source unknown--if anyone recognizes it and can give me the original
name and source I would be grateful) ; the other is Frog Pond Green (a
variation on Steve Hansen's high calcium mat base).
And finally, as a reminder, if you have tested any glazes and are willing
to share the results, please send them to me. While I will probably
eventually get them directly from Alfred Analytical if you gave them
permission to send them to me, that is a slow process.
Happy glaze testing,
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"
John Hesselberth on sat 8 jan 00
Ilene Mahler wrote:
>Have you taken this glaze down to cone 5 Thanks Ilene in Conn
No, but I'll virtually guarantee if you do you will get more copper
leaching. It may be a little more or it may be a lot more, but it will be
more. Why don't you test it that way and tell us the results.
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"
Tasha Olive on sat 8 jan 00
John, I have used xavier jade as one of my main glazes for over a year and a
half now and even made an entire dish set of it for my own personal use.
only did so because a lovely bowl I had made was holding up so exceptionally
well through heavy and often dishwasher trips. My dish set is still just
like it was when fresh out of the kiln - showing no signs to cause concern
of leaching. Very glad to see the results as I'm loving this glaze more all
the time. Tasha in (cold!!!!) Roswell, N.M.
-----Original Message-----
From: John Hesselberth
To: CLAYART@LSV.UKY.EDU
Date: Wednesday, January 05, 2000 3:10 PM
Subject: A great, stable cone 6 green semimat glaze
----------------------------Original message----------------------------
Here's some great news on a green, copper-containing satin mat glaze that
is very attractive. The original test work was done by Clayart member
Heidi Haugen--thanks Heidi for taking the lead on this one! She had
tested at Alfred Analytical a glaze she liked called Xavier's Warm Jade
Green (source: Cushing's Handbook). When she sent the results to me for
comment it looked so promising that I decided to test it a little more
extensively. The results from those tests are back now and this is the
best high-copper-containing glaze I have seen when it come to glaze
stability in the standard leaching test. It also happens to be a very
attractive cone 6 satin mat or semimat.
As you will see below, the results are a little scattered; however I
don't consider this to be unusual. There is a fair amount of
experimental variation both in mixing and firing glazes and in the
analytical work to measure leaching performance. The point is all of
these numbers are pretty low compared to what I have seen in other
copper-green glazes. Here are the recipe and the results--you be the
final judge.
Xavier's Warm Jade Green
Custer Feldspar 40.0
Frit 3124 9.0
Whiting 16.0
Talc 9.0
EPK 10.0
Flint 16.0
Add
Rutile 6.0
Copper Carbonate 4.0
Unity Calculations
K2O 0.134
Na2O 0.088
CaO 0.562
MgO 0.216
Al2O3 0.343
B2O3 0.055
SiO2 2.988
Heidi tested the glaze as written above. I tested it with 3, 4 and 5%
copper. I also tested for boron on the 4% sample. Here are all the
leaching results.
Heidi's test 4.0% CuCO3 4.2 mg/l Cu
John's tests 3.0% CuCO3 2.75 mg/l Cu
4.0% CuCO3 0.68 mg/l Cu, 0.04 mg/l B
5.0% CuCO3 3.07 mg/l Cu
Yes, as I noted above, there is some unexpected variability--I certainly
wouldn't expect 4% Cu to have lower leaching than 3% copper. However I
expect if I repeated these test 10 times and averaged the numbers they
would fall right into line with expectations. The boron leaching is so
low it is not worth a second thought. The exiting thing to me is that I
have tested 2 other green glazes that are very similar in appearance to
this one and one leached 15-30 mg/l Cu while the other leached about 5-15
mg/l Cu. This one is clearly the best of the lot. As I explained a few
weeks ago on Clayart, while there is no standard for copper leaching, my
personal goal is less than 10 mg/l and Monona would challenge us to
approach the water limit of 1.3 mg/l. This glaze clearly is better than
my own goal and approaches the water limit. It is, of course, far better
than the 15-30 which is the best I had seen a year ago when I started
this work. You can bet I will be testing this glaze in larger scale and
switching to it if it continues to look good.
If you are interested in examining the results from all three glazes,
they are on my web site (URL below). One is called Gray-Green mat
(source unknown--if anyone recognizes it and can give me the original
name and source I would be grateful) ; the other is Frog Pond Green (a
variation on Steve Hansen's high calcium mat base).
And finally, as a reminder, if you have tested any glazes and are willing
to share the results, please send them to me. While I will probably
eventually get them directly from Alfred Analytical if you gave them
permission to send them to me, that is a slow process.
Happy glaze testing,
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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