This pottery was made from gray clay usually with a lead glaze. Iron oxide was added to give some a purple color. These were fired at higher temperatures. It has blue color patterns from colbalt that is added to the lead glaze. Before this century porcelain was made only in China, and it was very expensive.
Porcelain is clay heated at very high temperatures so that it turns glass like.
Too see how an Indian burial sack is prepared for museum display see Indian Burial Sack.