If it's a genuine sand
patina, it shouldn't be affected any more than any coin with a sandy
patina is affected by a wet wipe, which most likely depends somewhat on how long it has been 'in circulation' after being unearthed. My experiences are somewhat limited but one coin I
had looked dirty and just generally unpleasant with detail hard o make out and it turned out that it
had been waxed. After removal of the wax I
had a beautiful coin that no one in their right mind would want to clean or wax.