It is amazing now similar different ball clays are. Clearly, soluble salts are an issue with all of them (the brownish scum). These bars are much cleaner on the backsides (since the solubles were left on the surface on the fronts during drying). The drying shrinkages, plasticities and fired maturities are also all remarkably similar.
In ceramics, porcelains lack plasticity and fire to high density with white, glassy surface. Stonewares are plastic and fire cream to brown and lower density, Porcelaineous stoneware are between these two.