Hi,
I have some engraved zippos I am planning to engrave for groomsman gifts. I’ve only engraved woods and acrylic so far. I thought I had read certain metal finishes can ruin the laser. Is a chrome finish ok to put in the glowforge? If yes, does anyone have any recommended settings 
The Glowforge cannot engrave any metal. It can, however, mark metal with a marking agent such as CerMark.
To expand a bit on @dklgood’s excellent advice, check out #11:
If the Zippos are painted or powder coated, you can run an engrave operation and it will burn off the paint/powder coating leaving you with a silver “etch”.
I think it’s copper that you don’t want to put into the laser, due to its high reflectivity in a CO2 laser. Probably alloys that are high in copper (maybe some brasses? Unsure about this) would also be problematic.
got it! Thanks for all the advice!