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Published Jul 5, 2022

Handbuilding with porcelain has a well known problem: it often warps. And when you are doing a lot of beautiful detail work like Claire Prenton, warping is unacceptable.

So Claire found a solution with upholstery foam. By trimming upholstery foam down to a tapered cylindrical shape, Claire gives her pieces the support they need to survive lots of handling. In this Quick Tip, excerpted from the Ceramics Monthly archive, Claire gives you all of the details you need to make yourself some of these helpful homemade tools! –Jennifer Poellot Harnetty, editor


Claire Prenton’s cup, 4 in. (10 cm) in height, handbuilt porcelain, glaze, fired to cone 6 in oxidation, 20-Karat gold. Handbuilding with porcelain has many benefits and one well-known problem: it often warps. But don’t worry, there is a solution: upholstery foam supports.

One of the things that really excited me when I started to work with porcelain was how lightweight my pieces could become. The desire to roll ever-thinner slabs for my cups also came with some issues. I make highly decorated and embellished surfaces, which are stamped, carved, incised, slip trailed, and sprigged. I was finding that it was almost impossible to work on the detail of the cups without distorting the shape. Working with them resting on a board was awkward and really uncomfortable for my neck. I needed to be able to pick them up and work with them in my hand, that way the design could flow organically. I wanted to be able to hold the cup in any position while incising the design with my craft knife. It is a common problem for hand builders when making cups or tumblers to keep them perfectly cylindrical. Compression can be added by going over the piece on the wheel, but this wasn’t an option for me due to the amount of surface decoration.

Evolving Studio Practice

Like most potters I have many handmade tools; one of the things I love about pottery is that you are always evolving in your studio practice and problem solving. Improvisation becomes part of day-to-day studio life. I had a collection of 12-inch-square pieces of upholstery foam, the sort used for chair cushions; I rest delicate pieces on them while working on construction or brushing on glaze. To solve my issue with distorting the cups as I handled them, I decided to use the foam in a different way, as an interior support.

1 Create a template of the cup’s inside diameter. Use the template to draw and cut out circles of upholstery foam.2 Squeeze the foam support and carefully place it inside the cup.

 

3 With the foam inside the cup, work on the cup’s surface details and attach the handle. The foam support can be left inside the cup, while it is wrapped in plastic, to slowly dry. Remove the foam once the cup is dry.I first cut a card-stock template the size of the inside diameter of the cup, then with a permanent marker I drew around the template onto the foam square. The foam is available in different densities and the lightweight, soft foam works best for these foam support disks. The disks are cut out using scissors. I found trimming the foam into a tapered disk not only worked well as it echoed the shape of my cups, but it also provides a little more wiggle room with fit. I want the foam to fit snugly but I don’t want it to put pressure on the cup walls.

The foam disks are then placed inside the cups, making them easy to handle and providing that extra support. The other advantage of using the foam disks is that you can compress the foam when placing it inside and removing it from the cup and therefore don’t leave any marks on the inside of the cup.

Working with such delicate, thin slabs of porcelain, the weight of the handle would also cause it to distort the shape during drying. I found that keeping the upholstery foam inside the cups while they were slowly drying ensured they would stay perfectly round. I could also adjust the size of the foam to allow for clay shrinkage just by lifting the tapered foam out a little after a day or so of slow drying. I want the foam to be there as a reminder to the cup to remain in the correct shape, but not to put pressure of the cup walls, which could cause it to crack. After a couple of days of drying, I remove the foam disk all together as its work is done.

**First published in 2018.