I have researched our site for discussions on discoloring of very old porcelain. I have noticed a lot of good offerings. I came to a conclusion that I was going to try Howard’s Feed N Wax. I was really impressed with the results. I posted pics of the two signs (before and after). I treated each sign...generous application...let sit for 20 minutes...wipe off excess...polish with cloth. Impressive!!! Thought I would share the results.