In the comments to the tinfoil fake video I mention above, there's a real cracker of a comment. It's by a metal detectorist, he gives his name, but you can look it up.
[...] The half crown i found last week is realy worn how come. Is it because of the soil[?] i did the spit and foil test and it did smell like sulpher so i do think its silver but why do the get so worn. I have found a victoria 3 pence dated 1901 and half of it is peeling away is that a forgery. Cheers fella good vid aswell. H.H[HH is "Happy Hunting", for more artefacts to break].Yeah, I'm sure many metal detectorists are wondering how things like this happen.