Underglaze Blisters

[Paddy O]

I teach ceramics in middle school. We use porcelain, bisque then under glaze stains to decorate, covered in a clear gloss glaze. Fire to cone 10. Mostly this is all good. Sometimes a glaze blisters over the stain. I assume this is because the stain is applied too thickly and so the glaze doesn't stick.

Has anyone else experienced this or have other reasons/solutions?

[TJR]

I am suggesting that you apply your underglaze to the leather hard pot. Let dry, then bisque and glaze.

I used to have all my students decorate with coloured slips on leatherhard clay, then we would bisque, and everything would get a clear glaze. Now that I am older and smarter, I just buy commercial glazes and we bisque and fire everything to cone 06.

TJR.

[Benzine]

I do the same as TJR.

 

For full disclosure, I tell my students, that underglaze can be applied on greenware or bisqueware.  But for everyone's sanity, namely my own, I generally require underglaze go on before the bisque only.

 

My reason, I've found that when students apply the underglaze, then clear on bisque, they don't let the underglaze dry enough/ press too hard with the brush causing the underglaze to mix a bit with the clear.  So they end up with less than stellar results.  

I know there are plenty of people here, who have no problem applying both underglaze and glaze, for the same firing.  But when managing twenty some students, I find being a bit more restrictive, is beneficial.

 

On a side note:  Porcelain with Middle School, Wow!  I can't think of any High School programs that use porcelain.  Seems like you have a well funded program.