What can be etched?

I have purchased a TBK 958A for iphone back glass replacements, but the insructions are…. non existent.

Anyway, I noticed i can etch things so i could potentially do persnalised gifts. My question is, if anyone has experience with this machine or similar, what materials can be etched, and what settings need to be changed (assuming so if different materials are used)

It seems to me from what i’ve done so far, it burns away the coated surface, so i’m assuming this type of laser doesnt actually etch into solid materials as such? Hence the reason I would like to find out what types of phone cases or other materials I can etch into and relevant settings for the materials?

Many Thanks