This note has been prompted by the recent analysis of the die used to strike the obverse of the Imitation Spade Guinea (ISG) produced for the bicentenary of the Macniven and Cameron company in 1970. In the 19th century the company used many ISGs to advertise its ranges of pen nibs. The note traces the history of the study of ISGs and where further information about the company can be found.
XRF analysis shows the die to be made from a high Nickel-Chrome steel with most surfaces contaminated with traces of brass (Copper and Zinc) from the tokens being struck. The die face, however, shows maybe 3% brass impregnated into the surface. This is likely metal dust trapped within the surface scratches and damage in the top few microns or tens of microns at the most.
BNS Research Blog 