aluminum foil, HOT water and baking soda. make sure the entire chain is completely under water.
get a plastic pan or glass (not metal) and place foil on bottom. add a table spoon ( = 3 teaspoons) or so and then add HOT water (boiling, since you don't have to touch it). stir the solution with something that is not metal, and place chain in water. wait for 10 minutes. come back, and wipe the chain down to see if varnish comes off.
if not, do it again, and replace the solution of course since the water is probably only "warm" now.
why does this work? go take a chemistry class.
if not, get some other chemical from some store...