Small Sculpture and Cracking Glaze

this sculpture with two others in 2015

I've been working on a couple pieces of sculpture since 2015. I built them in 2015, applied underglaze in 2016, but couldn't finish them until this year, maybe, because their surfaces are causing me an unusual amount of trouble.

the first layer of underglaze in 2016

The one that has caused me the most trouble is a simple vertical sculpture with three bulb shaped attachments. There's no problem with the structure itself, but I could not get underglaze to stay put. When I first applied underglaze, it seemed fine. I fired it in place, but when I went to apply a second coat of a contrasting color, the first coat started to crack off.

two layers of slip cracking off

I can't remember fired underglaze cracking off any other work I've done besides this sculpture and another made at the same time. Generally, if glaze or underglaze won't stick to a surface it is because there is wax, grease, or dust on the surface, but none of those substances should survive firing and scrubbing. I picked off the underglaze that was cracking and scrubbed the whole pot before reapplying another layer of underglaze, but after a second firing, that too cracked off in multiple places. 

slip cracking off

At some point in 2016, I got mad and just covered the whole thing with throwing slip. I didn't expect this to solve the problem, but I was annoyed and didn't want to look at the piece anymore. The throwing slip cracked too, of course.

 
wet slip (you can see the circles of underglaze through the slip) and dry, cracking slip from 2016

This year, I decided to wash off the slip and see if there was anything to be done for the piece. Bits of hard, fired underglaze were still cracking off and where they cracked, they left a sharp edge and change in thickness that would show up through a new coat of underglaze. 

grinding off the underglaze

I decided to use a wire wheel to grind off as much underglaze as I could. Grinding off the underglaze was satisfying but messy. Mostly the underglaze cracked off, sometimes it required grinding, and in one section, the red underglaze was adhered so well that grinding didn't budge it--at least the amount of grinding time I was willing to commit didn't budge it.

the red that wouldn't grind off

At the tight corners, the wire brush was too thick to reach the underglaze. As it wasn't cracking, I decided to leave it alone. The transition between the raised level of the underglaze and the raw ceramic was more gentle than where the underglaze cracked off, so I guessed the depth change wouldn't show through the next layer of underglaze.

the wire brushed sculpture

I kind of like the ground texture of the raw ceramic. The sand and grog has become visible as the smooth ceramics surface was ground away. The rougher texture makes the surface look like cement, but the overall result doesn't feel like something I had much control over. The hard-to-reach crevices show up purple and blue and the hard, irregular red section looks out of place.

the wire brushed surface

I decided to reapply a red underglaze over the body and purple over the already purple bulb/leaf shapes and just fire it with a gloss over the top of everything. The piece is now "finished." It doesnt' appear to be cracking, but neither is it all that exciting to look at. Though a lot simpler than many of my other pieces, its surface required much more effort than what shows up in the piece now.

the "finished" piece from 2015

As I was getting pictures ready for this post, I pulled the masking tape off of the other vertical sculpture from 2015 (seen in back right of the first picture in this post). I had masking tape in place to hold on a bike part I had epoxied in place to complete the piece. When I pulled off the masking tape, it pulled a cracked section of glaze and underglaze off the surface of the sculpture. Sigh.

glaze cracks show up (today!) in the other sculpture from 2015