With all the whacky ideas we've had about grounds and wood treatments lately, how about something which sounds a little more simple and plausible?
Encapsulating the instrument or the wood fibers in limestone?
Stalactites and stalagmites are formed from the dissolved minerals deposited by mineral rich water. So is the hard-to-remove bathtub scale in "hard-water" areas.
Calcium carbonate can be dissolved (up to a point) in water containing carbon dioxide... carbonated water, club soda......., and supposedly goes back to its original chemical makeup when it dries.
I don't know how "hard" the well water around Cremona is, or the water in the Po river. Perhaps the mineral content can be concentrated somewhat (before it starts precipitating) through partial evaporation?