 The bases on which the figures sat were covered with silver, later torn away, and these sections are left blank in the engraved reproduction above.It is an important example of ancient metallurgy, its surface being decorated with a variety of metals including silver, gold, copper-gold alloy and various base metals.One of the metals employed is black, made by alloying copper and tin with small amounts of gold and silver, and then "pickling" it in organic acid.