glazing question

[Ann H]

Does anyone know if it is possible to convert a cobalt blue cone 10 oxidation glaze into a formula for reduction firing?

Recipe: 

kaolin, 36.21

wollastonite, 23.14

Neph Sy, 22.79

Firt 3134, 14.56

Silica, 3.31

Cobalt Oxide, 1.00

 

[Callie Beller Diesel]

You don’t have to do anything to that glaze to fire it in reduction. For the most part, cobalt blues don’t change a great deal from reduction to oxidation. The differences will mostly result from the change in the clay body underneath it.

[Bill Kielb]

some thoughts here that may help
Only a handful metalic oxides will change color significantly in reduction. In glazes popular would be copper (to red), iron ( lots of possibilities here). Iron in the claybody will react as well. Cobalt glazes along with the claybody will likely take on a different look but testing is the only way to tell. Any cone ten glaze can fire in a cone ten reduction, those without the magic few oxides will still likely appear differently than in oxidation though - generally glazes and bodies appear more muted.

So glazes “made“ for reduction often contain reactive metal oxides to change color or depend on iron for variegation and or crystallization. Carbon trapping is another look that is common as well, but occurs most often “by design” with glazes relying on soluble carbonates.

Your glaze will very likely appear different in reduction than oxidation, but test fire it on a test tile (your clay) to understand what the look will be.

Last thought - your glaze contains boron in the use of fritt. Cone ten glazes generally do not require boron, so I am not sure of this formulation and it’s intended melting point.

a good read - digital fire, reduction https://digitalfire.com/glossary/reduction+firing

In the digitalfire article, he has some cobalt blue examples as well. I guess I would also ask, what look are you expecting or seeking?

Edited August 9 by Bill Kielb

[Ann H]

Thank you both, this is very helpful!

[Ann H]

Bill, to answer your question, here is the cobalt blue look i’m going for. It is the test tile on the right.

[Bill Kielb]

22 minutes ago, Ann H said:

Bill, to answer your question, here is the cobalt blue look i’m going for. It is the test tile on the right.

 

Very nice, looks a bit drippy though. Might confirm my thought about the amount of boron in that recipe fired to cone ten. As long as you understand its performance and is the color and texture you are seeking, likely a win! Seems like always fire on a cookie, stop the glaze a bit from the bottom to minimize, etc….. I think Tony’s cobalt examples trended towards a lighter blue. Always good to test, nice!

[Ann H]

Thanks☺️