I feel sure that you are right.
The thing is, that ladies who are sensitive to silver usually just stay away from it, and where they do want to wear a special piece of silver jewelry they are most likely to reach out for a tiny vial of nail polish rather than keep a litre of polyurethane or other commercial product.
Nail varnish is very good for such a job because it is a very hard finish which needs acetone for removal, and it's right there on the make-up table. It easily lasts for the day.
Today I am making a hardwood blank of a ring for forming another mold, one to take a nice opal stone on the finished item. Then , if by any chance I fail at first casting attempt I can re-use it over and over.
I can't wait to get that new torch........