From the manufacturer:
Glaze is a unique type of decorative art pen with raised writing you can feel! Glaze writes well on plastic and non-porous surfaces. It can be used to decorate invitations, cards, CDs, vellum, plastic and for rubber stamp embellishments. Sold in packs of two pens of the same color. Meets ASTM and ACMI non-toxicity standards and is AP seal certified.