I've been making some big tiles lately with underglazes applied on greenware and bisque, with a clear glaze on top, fired to 2185 F (1196 C). I use Laguna buff sculpture cone 5 clay because it hardly, ever cracks and is super strong after firing - and it does not craze with Laguna clear bright glaze. I make large slabs with this clay by hand. The tile in the photo above has an embedded porcelain pieces in the surface. Because the color of the clay itself is tan, I usually cover the tile/slab with white slip. This white background makes underglazes appear brighter and more vibrant. My goal is to make art out of each piece so I do different things to each one to make it one-of-a-kind. I like to use underglazes because one can get almost any color possible. Also, layering of colors on top one another other is easy, they don't move or bleed like glazes, and when applying them to the surface of the clay they look like a matte version of the piece after firing. Underglazes are a pleasure to use when creating ceramic artwork.