Invisible ink, when the ink write on the cards, it can not be seen by naked eyes, but can be seen by IR camera lens or contact lenses. This ink if you use for IR camera, then any cards is suitable, but if you use for contact lenses, then the red cards is OK and better under yellow light.
Eyemarkedcards also sells invisible ink for printer. We offer ink and technology and machine to help you to mark the cards for contact lenses. Also, we can offer you many kinds of latest ink for different contact lenses.