Overglaze As An Underglaze?

[centrific pottery]

I have succesfully used cobalt oxide mixed with water as an overglaze on my clear glaze. Is it possible to also put the cobalt oxide onto bisque ware and then clear glaze over it for the same result?

[bciskepottery]

A couple of test tiles or pots will tell you. One test could be a bisqued pot/tile where you put the cobalt oxide mixture on and then glaze over it. The second could be a pot/tile where you put the cobalt oxide mixture on a piece of greenware, bisque it and then glaze it.

[Marcia Selsor]

You can put cobalt under a glaze on bisque but it is tricky not to over do it...where it could burn or bubble if too concentrated.

The over glazing using cobalt in a glaze on top of a glaze is a Chinese technique.Marcia

[OffCenter]

I have succesfully used cobalt oxide mixed with water as an overglaze on my clear glaze. Is it possible to also put the cobalt oxide onto bisque ware and then clear glaze over it for the same result?

 

 

Sometimes substituting cobalt carbonate for cobalt oxide solves the burn/bubble problem. You could even try cobalt sulfate for a very subtle blue.

[Marcia Selsor]

I have used cobalt sulphate and found it to be a very strong blue. What do you use as a per centage? I also have a brightly decorated bowl by Sarah jaeger that had cobalt sulphate as a colorant. It is a brilliant cobalt blue among other colors.

Marcia

[OffCenter]

I have used cobalt sulphate and found it to be a very strong blue. What do you use as a per centage? I also have a brightly decorated bowl by Sarah jaeger that had cobalt sulphate as a colorant. It is a brilliant cobalt blue among other colors.

Marcia

 

 

Hi Marcia,

 

The same percentage of each of the three cobalts gives strongest colors in order: oxide, carbonate, sulphate.

 

Jim

[Marcia Selsor]

I have used cobalt sulphate and found it to be a very strong blue. What do you use as a per centage? I also have a brightly decorated bowl by Sarah jaeger that had cobalt sulphate as a colorant. It is a brilliant cobalt blue among other colors.

Marcia

 

 

Hi Marcia,

 

The same percentage of each of the three cobalts gives strongest colors in order: oxide, carbonate, sulphate.

 

Jim

 

 

I hadn't thought of it that way but that makes perfect sense. I use the cobalt ox. and carb. mixed with dry ingredients more often.

Thanks.

Marcia

[Deb Evans]

a little bit of cobalt oc goes a long way ....I've never used more than 3-4 % in clay slips, underglazes, glazzes, blue clay etc...usually you can go as low as .5 or 1% and get great blues. Have fun....