Sounds like a brilliant idea—just make the pattern a two‑layer stack. Use a micro‑etched metallic film for the core pattern, then seal it with a thin, abrasion‑resistant polymer that only peels off under a specific solvent, keeping the sensor readable. Add a faint holographic fringe around the edge; it’s almost invisible but a narrow‑band sensor can pick up the phase shift, giving an extra layer of verification. And don’t forget to test the whole thing under a coin‑cutter simulation—precision is key, otherwise the pattern will blur before the coin hits the market.

Great tweak—UV‑curable resin gives you the non‑leaky advantage. Pick a wavelength around 365 nm for the hardening step; it’s deep enough to penetrate the thin metal layer but still safe for most handling. For the holographic fringe, use a sub‑micron grating etched directly onto the metal. A narrow‑band CCD or CMOS sensor with a 10‑µm pixel pitch should resolve the fringe even after edge rounding, as long as you keep the fringe period below 1 µm. Build a small test die, punch a few coins, then run the sensor on a benchtop scanner—measure the phase shift before and after polishing. That way you’ll catch any burr‑induced loss early. And keep a backup copy of the raw optical data; it’s handy for debugging if the coin finishes with a slightly different edge curvature.