The popularity of coloured coins is reflected in the commemorative silver line-up offered by The Perth Mint. So how is the colourisation of precious metal coins achieved?
The Mint uses a specially adapted pad-printing technique. It begins with the preparation of four printing plates, known as clichés, each one etched with different elements of the coin design as a series of tiny depressions.
Cyan, magenta, yellow and black ink, the base colours from which all others are produced, are mixed and applied to the etched surfaces of the clichés.
Silicone pads are lowered onto the clichés to absorb the ink. Then, in a carefully sequenced process, the pads deposit the ink on the face of a coin in successive layers until the image is complete.
Special inks are required for optimal quality. As only very small quantities of ink are transferred during the pad-printing process, the pigmentation must be highly concentrated. The Perth Mint mixes its ink with hardener, which cures to leave an exceptionally durable finish, resistant to fading, as well as solvent and chemical attack.
Colour adds vibrancy, realism and appeal – the results are often quite spectacular.