I discussed these types briefly in my new book "Forgotten Coins" in the World Counterfeit 1500-1800 chapter. The realeswatcher piece is mercuric silver amalgamation (i.e., silver wash) over a brass, brass/bronze or copper host. The German counterfeiters like the English counterfeiters preferred copper host whereas the French preferred brass hosts.
John Lorenzo
United States
P.S. IMO its genuine. Debased silver issues just are not seen in these types - just the relaeswatcher types from my research of the last 15 years.