Nope. Those are a bit physical, and it’s the physical stiff that often does the damage.
Wrap the back of your renaissance painting in cling-film, and put it in the dishwasher. Turn it at intervals. Dishwashers were originally designed to remove dirt from posh plates without harming the gold leaf. If this doesn’t get through the varnish, you may need to replace the salt with something like fine carborundum powder.
…and don’t come crying to me when it doesn’t work.