There are a variety of materials which cannot be cut on a CO2 laser, but you can still engrave them.
Please see examples of materials that can be engraved only below:
Granite – Marble – Slate – Glass – Anodised Metal – Ceramic
As these are tough materials, a high amount of power is needed to engrave past the surface and mark the material, please use the below settings as a rough starting point.
Glassware – If you lay a wet piece of kitchen roll on top of the glass to keep it cool this reduces the flaking and will help to create a smoother, higher-quality finish. Turning off the air compressor can also help.
Metals – You can engrave onto some metals that do not have an anodised layer with the assistance of a thermal marking
spray or tape, there are many of these available but Cermark seems to be the most popular.