Vince wrote:
Recently had bathroom remodelled. The contractor was asked (politely)
to remove the "gunk" around the sink drain collar. He used his finger
nail to scrape the surface of the drain collar, which had a lacquer
finish. The (silicon) gunk remians.

When replacing that drain collar I will also want to remove the
silicon used as a sealant from the sink baisn where teh drain collar
sits. Any suggestions for a solvent for this purpose ?

Just try rubbing it off. If you want, you can spray some Windex on it
to see if it makes removal easier.