Are there any metal substrates you can’t laser engrave/mark?

Magnesium certainly can’t be laser marked due to its combustible nature. Raw metals without a coating shouldn’t be marked. The reasons are twofold:

1. Aesthetics. Marked bare anodized aluminum will leave a low-contrast (difficult to see) white mark on a silver background. Stainless steel will leave a blackened carbon mark if given enough power, but the amount of heat needed to generate the black mark can distort the metal and graphics.
2. Durability. Ablating the raw metal surface weakens and compromises the protective (oxide) coating which makes the metal more susceptible to oxidation and rust (e.g. black anodized or raw stainless steel). Marking pre-coated sheets (e.g. DuraBlack) or sprayed sheets (e.g. CerMark) protects the integrity of the base metal and leaves the metal surface intact and fully protected.

-Karly Baldi, Horizons Imaging Group