ᐅ Removing Wood Stain from Stone Tiles

Hello, I am asking on behalf of my father.

Last year, we treated our wooden fence and pavilion outside with a clear wood varnish/wood stain. Since the seller said the wood varnish could be removed easily with “turpentine/acetone” (Multichimica Acquaragia Extra) — presumably only immediately after application — we were not particularly careful, and some of the paint got spread onto the underlying stone tiles.

After a few hours, the wood varnish had already hardened, and continuous scrubbing with “turpentine” did not lead to any improvement. In the following days, we also tried other agents and even a steam cleaner without success.

The stone tiles have a thin, rough coating on approximately ceramic/clay.
Regarding the paint, I am not sure if it was a stain or a varnish. However, I believe it was a wood varnish, approximately an acrylic varnish.
Edit: I am not sure if this was actually the product used, but my father mentioned possibly: solvent-based protective stain – Arreghini classic (hydrocarbons, C9-C12, n-alkanes, isoalkanes, cycloalkanes, aromatics. C9 hydrocarbons, aromatics. n-butyl acetate. xylene – isomer mixture).

Is there any way or solvent to remove the stubborn paint residues (brown stains in the attachment)?

I would guess that nitro thinner or acetone can remove it easily. But as always, please test it first on an inconspicuous area to make sure it doesn’t damage the tile surface.

Nitro thinner is available at discount hardware stores or places like Wreesmann and other cheap stores for about 2 euros.