Goopy, gloopy. Oozing, dripping. These are attributes of thixotropic clay, the properties of which are caused by deflocculation. The usual ways we work with clay are out of the question. “The clay appears to be firm but becomes increasingly fluid when manipulated,” writes Glenn Nelson. Thixotropic clay returns to its original state when it’s allowed to set. Graduate student Carol Jeanne Abraham developed a formula for porcelain with these properties. According to Nelson, it is made into a slip, then aged for a long time. Here is Abraham’s formula:
It is almost impossible to find information on thixotropic clay. Nelson’s A Potter’s Handbook devoted quite a bit of space to it, but I have seen nothing about this form since. This is one of the reasons for my post today. The clay body has such unique properties, it needs to see the light of day once again. In addition, Nelson passed away last April, almost a year ago and, while I will write a tribute to him another time, I am thinking of him as I write. His instructions for making a pot from thixotropic clay begin with directing us to stretch and fold the clay to activate its special properties. “Then gradually work it into a shape that can be draped over a mold,” he says. Leave it until it starts to set, then you can work with it again. The vessel needs to be taken off the mold as soon as possible, but he said “the surface may appear deceptively dry when the form is still quite plastic.” Working with thixotropic clay will take practice. Sagging is one of the problems you’d come up against. Also, Nelson said that, given its 6% shrinkage rate, glazes typically used for porcelain won’t work. He suggests using a glaze for cone 5 or lower. When the vessel is fired at cone 9, though, this glaze will craze slightly, he said. “The effects of fluidity and apparent motion will appeal to many potters, especially those interested in decorative and sculptural forms,” he concludes. When I think of Glen Nelson, I am reminded of university days, when we experimented with forms, textures, glazes, and clays. To me, thixotropic clay reminds me of those days…undefined territory, effort, and the joy that comes from learning and playing. Hats off to you, Glenn Nelson….