Glazes

Approach

Ceramic glazes can be bought ready made up and raring to go - just order online, put in the studio, dip your wares in and fire - often to get a characterless finish no different from everyone else who buys the same glaze, and with no real input from you as maker. This may be fine if you are a painter, and the glaze is a tool to help you create your images on your pots, but for those like me where the glaze is the finish, with no painterly effects, this doesn't let you create any individual effects. The approach I take is to develop my own glazes from the raw materials, though often building on the works of others, be they other contemporary makers, or Chinese potters from a thousand years ago.

Of course, thought also needs to go into the purpose of the glaze. Should it be seen as a glossy decorative finish, with the underlying clay just providing the form and the canvas, or should the clay and the glaze be seen as an integral whole, the glaze reinforcing the earthy nature of the clay? And, for functional pieces, of course the glaze must be food safe, durable, resistant to cutlery marks, and fine for the dishwasher and microwave.

 

Technology

Developing glazes is a fascinating combination of science and experience. There are so many variables of materials in the glaze, glaze thickness, firing temperature and duration. Whilst there are occasional random breakthroughs, a lot is down to methodical scientific process, testing a range of glazes with a number of variations and understanding the underlying chemistry. The tools I use are:

  • DigitalFire for storing glaze recipes and analysing their composition
  • To test glaze melting and textures, Currie Tiles as developed by the late Ian Currie
  • Filing large numbers of test tiles, all carefully recorded in Digital Fire - a photo cannot give you the feel and texture of a glaze, nor can it easily capture the complexity of some glossy variegated glazes
  • Digital scales, measuring cylinders, syringes and other tools for accurately measuring out glaze components
  • Dust mask, gloves and mop as some of the materials used can be a health hazard, particularly as powder or dust
  • An ever increasing library of current and historic books on glaze chemistry

 Glazes are essentially similar to glass, but with the added challenge of having to stick to the pot as it expands and contracts during firing. Silica is the main component of the glass element in the glaze, though other materials such as boron or lead can contribute to this. Modifiers such as aluminium oxide may make the molten glaze less runny. Fluxes like feldspar and barium help everything melt at lower temperatures. Colourants like iron, copper and cobalt give colour to the glaze. But, as you look into things further, things are not that clear cut - the role of materials can change, so it can act as a glass former in some conditions, a modifier in others, as well as affecting the melting point of the glaze, and modifying the colours produced.