Jon, the uranium pottery glaze is a distinctive orange-red color, not purple. The brand in question would be Fiestaware and I would be perfectly fine drinking from such a cup provided the glazing was unchipped and otherwise intact. Uranium and its decay daughters are primarily alpha emitters, ergo they are completely safe to use in a glaze as long as you aren't ingesting pieces of it (from chips). It is somewhat less suitable for plates because those get damaged by silverware more readily.