Underglaze

[fruch]

Last semester I had my students create mandalas on plates. Some of them threw them on the wheel and others made them out of slab . We use a low fire earthenware. I have them creating the mandalas using the sgraffito technique so we are carving onto leather hard clay.  I am letting the plates dry all the way before I fire to ^04. The problem I am having is the underglaze is chipping off the bisque after the firing. So I am wondering if I am firing to hot, if the students are putting the glaze on to thick or if the underglaze is bad, does one color chip easier than another? I am using ^05 underglaze by AMACO. I went ahead and had these kids put a clear coat on their plates but  the clear coat chipped off as well. Does anyone have any suggestions or know of an old thread I can read to help me? I tried to attach a picture but it wouldn't take my file. 

[oldlady]

resize your picture and it will work.  Paint lets you set the size easily.  i use the 600 x 450 pixel size which is a good size to see detail.

[Chris Campbell]

My guess is that the underglaze is being applied too thickly and not soaking into the clay but resting on top of it.

Thin out the underglazes to a cream consistency ... it is amazing how quickly they thicken up in the jar.

It is natural that the glaze would pop off since the underglaze is not holding on to anything.

If they want a darker color after bisque firing, they can always add another coat then bisque again.

[fruch]

ok, thank you. I will try thinning out the colors.