This is an example of how soluble salts can enhance the appearance of the fired surface of a cone 10R clay. This sculpture body is a vitreous dark brown burning base having lighter colored 20 mesh grog particles. The one on the left uses native stoneware clays that contain natural flux-containing solubles that migrate to the surface during drying. When fired they act like an extremely thin layer of glaze, producing a darker sheen on the surface. The thickness (and thus color) varies with contour and exposure of the surface during drying. The inside of the cone has no solubles at all.
In ceramics, clays with added aggregate are free formed or molding into shapes that are slowly dried and fired in a kiln. The process requires much skill.
A common problem with dry and fired ceramic. It is evident by the presence of a light or dark colored scum on the dry or fired surface.
Grog is a term used in ceramics to describe crushed brick (or other fired ceramic) aggregate that is added to sculpture and structural clays to improve drying properties.
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