Hi Norman,
when I said 'caustic' I should have said 'alkaline'. I suppose the effect on the metal surface would be akin to an etch with ,say, vinegar. The 'thinners' is a solvent and would not react with the metal, but can be a little messy, but it works extremely well. I have a Finnish Puukko which some fool had daubed with red paint (all over the curly birch handle.) Thinners and several cloths later, I easily removed the offending paint without damage to the birch
Hope this clarifies things.
Regards David