Best I could find: https://www.nisshametallizing.com/en/how-holographic-paper-made https://www.nisshametallizing.com/en/how-holographic-paper-m... I imagine in

Best I could find: https://www.nisshametallizing.com/en/how-holographic-paper-made https://www.nisshametallizing.com/en/how-holographic-paper-m... I imagine in the case of mixed printed/foil cards that they've printed ink on top of whatever clear layer protects the diffraction grating, leaving a gap anywhere they want the card to be shiny.