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While they are intriguing, with many low mintage pieces, I frankly think that modern Chinese overall is pretty boring, and that the older material is much more interesting, even if we're only talking about turn of the century pieces.
Silver proofs have a more mirrored finish than the regular circulation issues. Also, it's more of a white color rather than the greyish white of nickel.
Metals do not necessarily tarnish - it depends on the climate and conditions they're stored in.
Late Victorian pennies with full luster and their original brilliant orange-red color are not infrequently offered for sale, to use one example.
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Your coin appears to be a poorly made cast copy of a halfcrown in brass, with the silver plating long worn off.
Counterfeits of British silver coins in lead and brass are known to have been made at least until the 1920s.
It's not uncommon to encounter 4th century Roman bronze coins that have been cleaned by a variety of methods, and/or coated in wax, lacquer, or other coating.