Clayboard is a relatively new discovery for me. It is a hardboard panel that is coated with a clay surface. Originally created for oils and acrylics, there is a new line of clayboard designed for watercolors. I was introduced to the watercolor clayboard at the Portrait Society's conference in May, and have been anxious to try it.
One thing I don't like right off the bat is having to confine myself with a standard size. Most of my paintings are cropped and recropped as I work, so this will be a big limitation for me.
Having said that, my first impression is that the surface is really nice to work on. The paint sits on the surface, but doesn't pool or run. This painting will undergo many changes as I am interested in seeing how the surface will handle mutiple layering and reworking. The brand I am using is Ampersand textured clayboard, 11x14".