I had always thought that differences in discoloration among pieces in the same dinner service was just due to some of the pieces being used more than others, and thus more subject to the heating and cooling that causes crazing and allows stains and dirt to get into the body. You're certainly right, Tim, that some earthenware bodies simply resist staining better than others, and that many earlier pieces look a lot better even now than the later, more cheaply produced wares.

As to your question about the advent of gilding on earthenwares, you see transferware from the early 19th century that is gilded. I know of pieces by Miles Mason and Ridgway and there were surely other manufacturers that used gilding, and other overcoloring, in an effort to spark new interest in their patterns. But I don't know how often it was done and you're right that it became widespread in the late 19th century when the English potters were competing with the Limoges factories and other European makers. Just my two cents worth.