Hello,Welcome and thanks for your question. Can you tell me what you mean by "French polish?"
I am familiar with the furniture finishing technique called French polish, but not with any particular polish called "French polish."
Looking forward to hearing from you,
I bought "French polish" in a tin. It contains shellac.
The medium used in the French polishing technique is shellac dissolved in alcohol. It can be dissolved in an alkaline solution. Things to try (in order) would be ammonia, sodium borate (Borax), sodium carbonate (washing soda or soda ash). You can buy these at the home improvement store (Lowe's, Home Depot). Sodium hydroxide should also work but be very careful with it to avoid burns. Be sure to use gloves when dealing with any of the solvents.
All the best,
Thanks very much - I will try these to see if they work.