 The helmet and visor were cast from an alloy consisting of an average of 82 % copper , 10 % zinc and 8 % tin . This alloy was probably derived from melted @-@ down scrap brass with a low zinc content , with which some tin had been added to improve the quality of the casting . Some of the fragments show traces of a white metal coating , indicating that the visor would originally have been <unk> to give the appearance of silver . The griffin was cast separately from a different alloy consisting of 68 % copper , 4 % zinc , 18 % tin and 10 % lead . The visor would originally have been a silver hue and the helmet would have had a <unk> yellow appearance . The helmet 's creation can be dated to the late 2nd or early 3rd century from the use of a particular type of decorated <unk> as well as some of its design features , such as its pierced eyes . 
