It was quoted that his were made of nickel or German silver .
from the article .
The mention of machinery (rather than moulds) points to the likelihood that the method of manufacture was that used in another enterprise of the same James Steele, with Robert Ramsay, from 1927 to 1930—when they were detected through the superabundance of coins bearing the same date. Halfcrowns dated 1920 and 1921 were then made from nickel 'or German silver'; the charge was of having a puncheon, four dies, an electrotyping machine, a rolling machine, an edging machine, a charcoal stove, an annealing box, electro-plating tanks, frames, an hydraulic press, and an ejecting machine . . . 'These misdirected geniuses had perfected what was virtually a miniature Scottish Mint'.7 In the early nineteen-sixties this remained the only successful case in which counterfeiters had struck pressed sheet metal in the same manner as the Royal Mint.