Platinum Sovereign - Victoria Spanish Copy

From around 1860 to 1881, Spain produced platinum counterfeits of English sovereigns, particularly between 1861 and 1872. Limited information is available about these counterfeits, which were made by alloying platinum with copper to achieve the desired density. After being struck, the coins were gold plated, resulting in highly effective forgeries. This practice likely ceased when platinum prices rose above its worth as a counterfeiting material. For more details, refer to G.P. Dyer's article, "Counterfeit Sovereigns in Platinum," in the Bulletin on Counterfeits, Vol. 4, No. 2/3 (Summer/Autumn 1979), pp. 30-5.

Other references: 

G.P. Dyer, “The Counterfeiting of Sovereigns in the Nineteenth Century,” Numismatic Chronicle (1966-), Vol. 172 (2012), pp. 287-292 (8 pages), published by the Royal Numismatic Society.

cf. Marsh 44