Micromachining of optical features and their transfer via stamping on precious metals

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The Royal Canadian Mint (RCM) is a leader in the coin making and coin collection business. Today it stamps metal currencies for numerous countries and is renowned worldwide for its strong research and innovation. To remain a leader in the minting industry, to keep its competitive edge and to attract other countries to stamp their metal currencies, the RCM is now looking into new anti-counterfeiting features and new ways to produce optical designs and special visual effects on coins. In a previous NSERC-CRD grant, we demonstrated that surface morphologies produced by ultrafast lasers can be used to colourize metals. We showed that fixed colours (i.e. independent on viewing angle) can be produced at speeds in line with industry requirements. While laser writing speeds are in line with the minting of numesmatic coins (i.e. collector coins where short series are produced) they are still inadequate for minting bullions and for circulation coins where minting rates are very high. The ultimate solution for the RCM would be to use their current stamping process to transfer these optical effects on coins. The goal of this NSERC-CRD project is to assess the viability of the RCM stamping process in the transfer of optical effects on precious metals (mainly silver). In the stamping process, features will first be engraved on a steel die using a laser or high precision milling machine, which will then be used to stamp coins and transfer the features and resulting optical effects onto the coin. The optical effects sought are holographic features where colours change with viewing angle and three-dimensional effects. If the RCM were to successfully stamp optical features on precious metals, it would maintain its leadership position in the coin making industry.