Peter Illsley
The Challenges of Crystals
The creation of crystalline glazes is one of the more difficult challenges a potter can face. Since the 1850’s the process has fascinated and in some cases obsessed a small number of potters in various countries. Peter Illsley, who has been potting professionally since 1963 and has had periods of playing with crystals at roughly five-year intervals. In January 1989 he made a total commitment to the problem of consistently producing quality crystals.
Hundreds of firings were done and hundreds of pots scrapped before he was able to achieve his goal.
He is the author of Macro Crystalline Glazes, a book for potters and collectors, which was published in hardback in June 1999 by The Crowood Press.
Illsleys porcelain pots are sprayed and dipped with zinc silicate glazes, which are seeded with titanium at 1300 degrees centigrade to form the nuclei of the spectacular flowers which then develop organically during an 1100c soak lasting up to five hours.
The peak temperature is critical – a few degrees too much will cause most of the glaze to run off the pot, consequently the pots have to be fired on their own pedestals, with a small bowl to catch the glaze run-off. Otherwise they would be welded to the kiln shelf. Too low a temperature produces something akin to galvanised iron! The clay, the glaze composition, its application and the firing cycle all play a vital and complex part of the transformation.
The variables are phenomenal and for me that is one of the great fascinations of the process, says Illsley. The number of crystals forming in the glaze and their location on the pot cannot be precisely controlled. But with careful attention to every detail of the making process, which is enormously time-consuming, some repetition of fairly similar characteristics can be achieved.
When I first managed to produce well-defined and reasonably sized crystals I had a fantastic feeling of achievement. The delight is still with me. The challenge to produce new variations of form and colour is still there. My experiment will go on.