Don't have a clue however if you figure it out please pm me and tell me. I found one identical to it about week and half ago. I found mine around old late 1800's home site. It was about 4-5inches deep. Let me know if you find out...thanks birdy1976
OHX ------Yes, what have there is deffintley a porcilein door knob
backing plate ,they were usually made of copper or brass from 1850's --early 1900'S have found several on the farm here
I believe it is a decoration used on a furniture drawer pull ring or knob.
I have an old bedroom dresser that was my mothers and it has a similar
piece on the drawers behind the pull rings.