Platinum Trial Coin of Nicholas I (1825-1855) 1827 Platinum diameter 27 mm, weight 21.24 g During the period from 1828 to 1845 coins with the value of three, six and twelve roubles were struck from platinum from the Demidov mines in the Urals. The collection has a unique series of platinum trial coins struck at the St Petersburg Mint with the dies of ordinary silver coins of 1826-1827 (a rouble, a poltina or 50-kopeck piece and a 25-kopeck piece).