Q: I’m making some ceramic sculpture and I don’t want to glaze it, I want to treat the surfaces differently. What can I do?
A: If the ceramic objects you are trying to color are not to be used for eating from, don’t need to sit outdoors, and you are not concerned with archivalness, just about any paint can be used. Any of these constraints limit your options. On bisqueware, the main problem is the absorbency of the clay body, which will suck the color out of the brush and leave craters on the surface. Try sealing the surface with progressively less dilute coats of (waterbase) gesso or use shellac. Once the surface has been sealed, you can paint with just about any paint—I’ve seen oils used very effectively.
Alternatively, to darken the surface somewhat and give a little shine, try rubbing on some shoe polish, then rubbing off the excess. If the piece must survive outdoors; mix some cement colors with some portland cement and water, then apply as a wash to your (unprimed) bisque surface. Any waxes or sealers you put on will have to be renewed periodically if the piece is left outdoors.