Very interesting...Found these doorknobs in a box of architectural salvage. The knobs could be porcelain or ceramic (they are heavy), with a random, gold leaf sort of pattern, embedded throughout, not raised. The knobs are as smooth as a pool ball.
The collars are etched. The only marking is "Dexter" on the door plate, a doorknob company. I couldn't find this design anywhere in their history, so it could be the hardware and knobs were put together, rather than created as a set.