5 replies to this topic

[Celia UK]

I recently used cobalt carbonate to fill a stamped motif on two small pieces made with white earthenware. I applied it when they were bone dry and cleaned up carefully (I thought) before bisquing in my electric kiln. There was cobalt residue on both pots which only showed after bisquing - very messy!  image.jpg   1.23MB   93 downloads  image.jpg   1004.14KB   73 downloads I know I could have had SOME on my fingers, but the cobalt appears to have spread during the firing. There was also some blue on another pot that was placed nearby in the kiln. I was able to clean them up, but it took some time! Any ideas as to how / why this happens and suggestions for preventing it another time.

Thanks.

[Marcia Selsor]

Cobalt is one of the strongest oxides and not easily detected when cleaning up. It is messy when used in that way. Sponge off really well.
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Marcia

[Pres]

I recently used cobalt carbonate to fill a stamped motif on two small pieces made with white earthenware. I applied it when they were bone dry and cleaned up carefully (I thought) before bisquing in my electric kiln. There was cobalt residue on both pots which only showed after bisquing - very messy!  image.jpg   1.23MB   93 downloads  image.jpg   1004.14KB   73 downloads I know I could have had SOME on my fingers, but the cobalt appears to have spread during the firing. There was also some blue on another pot that was placed nearby in the kiln. I was able to clean them up, but it took some time! Any ideas as to how / why this happens and suggestions for preventing it another time.

Thanks.

As Marcia says, really strong oxide. I use it on bisque fired ware as a wash, and then sponge off the high, or even sand if I want a crisp image. This usually works much better than on greenware. You could also try underglazes instead of the cobalt on your greenware, a lot less intrusive.

[Mark C.]

My suggestion is mix the colbat carb with a little glaze- on the bisque ware.We use coblat oxide in our black glaze but you could use a little white or clear glaze. My studio assistant makes bike mugs and the process is apply the glaze into the stamped motif with a small tipped applicator only into the groves-she then sponges off the extra this takes a lot of clean damp sponging then waxs over the whole motif and after that dries glazes the pot.The trick is to not spread it around.
This photo is a very old mug done like this.
Mark

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•  bikemug.jpg   157.44KB   46 downloads

[Chris Campbell]

Yes, it is the bane of shared studios because it is so hard to see before firing and even the tiniest fleck of it fires bright blue. It is possible that it floats during firing ... ? ... but also extremely likely to have floated off fingers and clothes before firing. One potter I know who decorates with it even fires her piece after decorating each segment so her hand does not inadvertently smudge or carry the dust to a clean part. So beautiful though!

[Celia UK]

Thank you for your comments and some things to try.

Celia