Underglaze Problems-

[Brandon Franks]

Hello,

 

My underglaze (AMACO Velvets) have had trouble with crystalline glazes. They keep matting(ish) and I think they are being *mixed* into the molten glaze at cone 10. I feel like I see little particles of the color throughout the top glaze.

 

How can I stop this, I apply the underglaze when the pot is leather heard, let it dry, and than bisque to 06.

[neilestrick]

Underglazes can get picked up and bleed when the glaze is runny. Dark colors like blue and black are more likely to do it. I do that on purpose on my pots. You could try a different brand of underglaze.

[liambesaw]

And some are refractory which would explain the matteness.  I've noticed it most with black and green.  You can try using less to help with that, though the color may not be as strong.  Maybe make a test tile with 1 coat, 2 coats, 3 coats and put it through a crystalline firing with your glaze on it.

[neilestrick]

If your glaze is being taken into the underglaze and going matte, your underglaze may be too thick. It could also be a case of the underglaze being over-fired and starting to melt, reacting with the glaze. I know of a couple of underglazes that do that at cone 6. Many underglazes are really made to work at low fire temps. Working with them at higher temps is always a gamble. A good percentage hold up fine at cone 6, but by cone 10 there can be troubles.

[Min]

If underglazes aren't working you could try a slip (or engobe) instead made from your claybody plus stain. It would be less fluxed than an underglaze.