Potters & Sculptors - Making Rock from Mud
5-10 years ago I mixed up a bucket of Pete Pinnell's Weathered Bronze Green cone 6-7. It was fine years ago and produced just the look I wanted. This time the results were not good. The glaze is very matt and is Dark gray only. No green at all. I first suspected it may have been that I needed to be at cone 7 down rather than cone six down. As you can see in the photo re-firing to cone 7 has not solved the problem. I'm now feeling that there has been a chemical change over the 5-10 year period. I can of course just mix up a new batch but then I would still not know what happened to the first old batch. I'd love to know why! Any educated guesses would be appreciated.
Recipe Name: Pete's Weathered Bronze
Cone: 6-9 Color: green bronze
Firing: Oxidation Surface: Matte
60 Nepheline Syenite
20 Strontium Carbonate
1 Lithium Carbonate
10 Ball Clay--Old Mine #4
5 Copper Carbonate
5 Titanium Dioxide
I found the same to be true, my older batch of Weathered Bronze no longer fires with any green in it so I went to the recipe below instead which seems to work even though it was mixed years ago.
STRONTIUM TURQUOISE MATTE ^5/6
The ingredients in this glaze are the same as the ones in Strontium Weathered Bronze; only the amounts vary slightly. A beautiful matte turquoise glaze!
60% Nepheline Syenite
25% Strontium Carbonate
02% Lithium Carbonate
09% Silica 325
04% Copper Carbonate
By eliminating Titanium Dioxide I think you have found the cause of "Weathered Bronze Green" interacting badly with some clays to create a mustard or ugly brown color. I'm going to mix up a batch of your recipe this Saturday and will post the results.
Titanium dioxide does not work like zircopax to provide a white background.
I once tried covering a darker clay with wash of titanium oxide, imagining I was covering a dark canvas with a ceramic guesso - boy was that a mistake! I got the same bubbly brown covering seen in Otto Wenger's container above.
The nepheline syenite in Weathered Bronze Green will leech salts over time after being mixed with water which will cause the glaze to hard-pan leaving you to apply only some of the components of the glaze. Weathered Bronze Green also began llife as a Cone 10 glaze which means it's under-fluxed for Cone 6. But I think in eliminating the Titanium Dioxide you've found the real problem.
Thanks to both of you for your insights. I have learned something and that was the goal. I will toss the old and give the new a try. I will post my results. Looking forward to seeing your results Norm.
Normally I'd use a gram of water for a gram of glaze but the Strontium Turquoise Matte has so little clay it tolerates less than half the water. Initially using more water the glaze wouldn't apply except on extremely porous bisques.
I made a strontium version and a barium version. It will probably be three weeks before the test tiles are fired, as "folks are working on the kiln".
I made Barbara's Strontium Turquoise Matte on the LEFT fired on four different clays.
and I replaced the Strontium with Barium on the RIGHT.
It's a typical Barium Blue as the Strontium or Barium shift the green color to blue, but not even close to a Weathered Bronze Green. Her recipe uses 25% strontium carbonate rather than 20% and leaves out the Titanium Dioxide.
What happens if you leave the lithium out
Lithium Carbonate or Lithium Fluoride are fluxes which make glazes runny. As a color, lithium contributes only a clear glass.
If you leave out the lithium, you have to replace it with more of another flux material like the nepheline syenite or the Ferro Frit 3269 which I add to my version of the glaze to be certain it melts at Cone 6.
The fluorine in the 3269 or in the Lithium Fluoride can add white whisps to the flow of the glaze.
Water Color Green has many of the same ingredients, lithium, copper, calcium carbonate, and strontium carbonate. But it's missing the Ball Clay, titanium, and Nepheline Syenite Both lithium and Strontium color-shift copper to a bluish tint by making the molten glaze more alkaline.
|108.2%||Water Color Green ^6|
|5.0%||Ferro Frit 3124 or change to 3269|