Expert: Sam Kelly - 8/20/2008

Question
* here is what we need help with: Why are our pieces coming out most of the
time with colors bleeding or moving?

We paint on bisque ware with duncan french dimension glaze, duncan concepts and mayco stroke and coat.

We use duncan clear dipping glaze (not brush on)

We cant even touch the colour once painted on the piece when dipping because it smears on our hands.

After firing we have places that have moved or bled.

Is there an alternative Glaze we can use? Are we doing something wrong here?  We can do the same procedure as mentioned above using same paints and Dipping glaze on Greenware and have great results with no problems! As soon as we move to bisque, color bleed, and movement galore.  Not to mention we have to be careful not to smear the colors on the piece itself after dipping.  Please help!

Answer
Hi Michael,
Applying two glazes to a bisqued pot is a much used process called 'Glaze on Glaze'. Using this process if one glaze has a fluxing material(helps the glaze to melt)that is discimilar to the other it can cause the glaze on glaze part of the pot to melt with more fluidity, hense the running of the glaze, or by putting one over the other you are actually making a different glaze for that part of the pot. The reverse problem to yours is that the top glaze peels back and pulls away from the glaze under it.

If you put your color on bisque , then rebisque before appling the clear coat, it may, and I stress may help with the problem.
The reason you can't touch the pot at bisque is because the absorbtion or sticking and drying of the color is much less than at the greenware stage, therefore requiring a longer period to absorb to or dry out on the pot. You may also be over bisquing, to high a temperature at bisque makes the pot more vitrified and less abrorbent.

Traditionally an underglaze is applied at the greenware stage, then fired to bisque, clear coat added and then final firing. Why you arn't having a problem with this method is because the color has been fired and sealed to the pot prior to clear covercoat application.

If you can decorate at the greenware stage without disrupting you processes I would suggest you do it.

Sam