Coloured clay is an ordinary body with a stain blended through it, so the colour goes all the way through rather than sitting on the surface. That is the whole appeal: a chip reveals more of the same colour, and techniques like nerikomi and agateware become possible. It is also why coloured bodies are the most expensive clays on most price lists.
Stained through, not painted on
Because the colour is in the body, a coloured clay can be cut, laminated, marbled and carved and still read as coloured everywhere. That is what separates it from underglaze or slip, both of which are surface treatments that a trimming tool will go straight through. For work built from patterned blocks of clay there is no substitute.
Why the price is what it is
Commercial body stains cost many times what clay costs, and colouring a body evenly requires blending a significant percentage through it. A dark or saturated colour therefore carries a lot of stain per kilogram. Suppliers list coloured ranges well above their plain bodies, and CTM's price list shows exactly that pattern across its coloured and special clays.
Colour through the firing
Stains are chosen for stability, but few are entirely unaffected by temperature and atmosphere. Some blues and greens hold across a wide range; reds, pinks and yellows are more temperamental and can fade or shift towards brown at the top of a stoneware firing. Test at your own temperature before committing a project, and keep to the range the supplier prints.
Working with several colours at once
Cross-contamination is the practical problem. A trace of dark body in a pale one shows immediately, so each colour wants its own wire, its own board area and its own reclaim, and hands and tools are cleaned between them. Working from light to dark through a session is the simplest discipline and saves most of the washing.
Questions people ask about coloured clay
Is coloured clay worth the price?
For work where the colour must survive cutting, carving or lamination, yes, because nothing applied to a surface will. For a coloured surface alone, slip or underglaze is far cheaper.
Does the colour fade in the kiln?
Some stains shift or fade at the top of a stoneware range, particularly reds and yellows. Fire a test tile at your own schedule before a project.
Can I make my own coloured clay?
Yes, by wedging body stain into a white body, and getting it even is the hard part. Commercial bodies are consistent, which matters if pieces must match.