Stacks: Testing Clay Bodies, Paint, Underglaze, and Papers

painted sprigs awaiting wiping and paper

After discovering that the increased scale of my stacked sculptures was causing cracking, I decided to test some alternate clay bodies under basically the same conditions. I created several similarly sized stacking forms, each out of a different clay body. I used paper for each one and glaze for the ones that did not crack in the first firing.

the three part stack with one type of sprig

I was happy with the amber paper and paint stack I finished last summer, so I decided to make similar forms for my tests, with areas for paper and other areas of sprigged textures. I complicated things by switching clay providers (because we were near Seattle and not near Tacoma for a trip) and making relatively minor some adjustments in my building methods. 

this piece cracked during drying

Throughout the years, since at least 2002, most of my sculpture has been built with coil and pinch methods. I use press molds for my bulbs and sprigged textures and I throw functional pieces on the wheel, but for most of that time, forms of any size have been primarily coil built. The biggest exception was the stacks I threw for the faculty show, Dust, in 2024. 

extruded coils being used for the building of one of the stacks

For most of my work, I have used rough coils shaped by hand, because they are fast and easy to make and use. However, for these large stacks, I extruded coils in order to maintain consistent wall thickness

my extruder with a long string of coil being readied for building

In the past, I've generally felt that the time it takes to set up the extruder, prepare the clay, extrude, then clean the extruder before building is not worth the hassle. With these tall stacks, because they are so big, and because I was trying to test the material strenth, I decided to start extruding my coils. The added effort of the extruding process is balanced by the amount of coils I use in one sitting. 

I tried out a new type of visible gallery for the top seam

The extruded coils allow me to build fast and since these pieces are large, I have been using about 75lbs of clay for "one" stack of three pieces. At this scale, the time spent extruding is a smaller percentage of the time spent building. It feels worth it to extrude coils, and they have the added advantage of consistency and speed (once the extruding is done).

because these pieces are so large, I start them on a counter, then lower them progressively to a stoll and then the floor

In response to the earlier cracks, besides testing clay bodies, I also started using thicker extruded coils for the first two or three levels of the base. Since most of my cracks were happening (or starting) in the bottom edge of the bottom section, I figured extra thickness here could help. I also started flipping my forms over after those first 2-3 rows to compress the bottom edge with a rib, before flipping the base right side up again to continue building.

the one-sprig piec with half a layer of acrylic paint

The clay bodies I tested were designed for sculpture and had either added grog (ground fired clay) or paper to help with strength and shrinkage control. Two of the three or four clay bodies I tested still cracked, which left me with a couple of options for clays that are working. Ironically, my daughter will be starting college at Lewis and Clark in Portland, meaning I probably need to test some sculpture clays from Georgie's in Portland if I want to save on shipping costs over the next 4 years.

the first gouache layer on the piece on the right, a paper mache and paper pulp experiement on a mold behind it

Of the two test pieces I made with sprigged sections and smooth sections for paper, one cracked and two didn't. I glazed the ones that didn't crack, but used acrylic and gouache for the one that did (the second cracked one is being used as a mold, to be discussed in a later post). I wanted to try some different colors of paper, so I bought some banana paper which worked fine, but the colors aren't as nice as the amber kozo paper I used last summer.

the base of the painted sprig piece while paper was being added

I used the underglazes much like I always do and am happy with them, but they don't contrast quite as nicely with the paper. I think the color contrast, as well as the texture contrasts worked particular well with the amber pieces from last summer.

the first layer of underglaze before firing

Lots of factors besides the paper color imapcted the finished pieces. For this year's painted stack, I used almost all the same shape of sprigs, which, with the less vibrant paper color, resulted in a more subdued form. I like the form on it's own, but I need to make an effort to get a well-lit picture that does it justice. 

the first layer of underglaze after firing

Additionally, I didn't realize that the metallic gouache paints that I used sparingly in the amber stack did quite as much to add some texture and shine to the piece. I was worried they might be overkill and thus didn't use any this time around.

the base with the second underglaze layer, fired glaze, and paper

For the glazed pieces, I have one that has a variety of different sprigs within each section, like last summer's amber stack. The other several different sections that each have the same sprig and color scheeme, separated vertically by smooth glazed sections.

the newest stacks (which no longer fit in my studio) waiting for a good quality photo sometime

Honestly, seeing all four of these stacks together makes me want to make even more pieces like these in future. I have several more stacks in progress, with no cracks and more complicated forms. I also just bought an additional 250lbs of clay, so I plan to start some new pieces next week, after we drop off the kid at college. The goal is that all of these end up in the faculty show in January 2027.