Anyone here ever take a specific gravity test on one of the "shipwreck effect" 8 Reales from this treasure? The coins are suppose to be .900 fine silver. I have read that seawater can leach out copper and other trace elements in these coins. I should guess that might make the ratio of silver in the coin to other metals higher; however I don't think that would change the specific gravity of a .900 fine silver coin.
I doubt it could change the specific gravity to the point where it could be detectable, but it might in extreme cases. With extreme cases being where the coin was so badly corroded that it was almost unrecognizable. I won't even pretend that I can tell you the specific scientific measurements for the differences between the rates of corrosion of silver and copper in salt water. But having done a bit of salvage myself involving silver coins and other largely copper objects like brass cannon on the same wreck, I can tell you there's not a whole lot of difference between the two in how they are affected by the salt water. As for salt water leeching copper out of a .900 silver coin, since it is an alloy, and a pretty evenly mixed alloy at that, the only copper that is possible to be leeched away is that found on the very outer surface of the coin. Of course the same thing goes for the silver. And both always seem to have corroded away at a pretty much equal rate.
