Revolutionary War British Admiral's Repousse Gilt button

Superb undug Revolutionary War (or earlier) period British Admiral's or Flag officer's gilt repousse button. Identical to Troiani , "Insignia of Independence " BNF.a. page 17. 21mm in diameter with a "sugarloaf" shaped bone back with 4 holes. Retains 85% of the original fire gilt and fragments of cords on the back. This was prescribed for Admirals in the Royal Navy between 1748 and 1795. . Perfect condition, none finer and 1 of ony 4 known examples.  Ex. Troiani Collection.