Our white ceramic rosettes are reproduced from one dating to the 1870's.  In Charleston they were used in formal areas of homes with white doorknobs with brass ferrules.  Sometimes they were silver plated.  Ceramic escutcheons completed the set. 
 
These have blind mount plates.  The ceramic rosette covers it and then the brass collar is threaded into the mounting plate to secure the rosette.
 
Sold each