I have access to one of those at school, I was always told that I couldn't engrave anything metal with it though. Even if I was only etching paint on the surface
Different lasers affect different materials. Find out what type of laser it is and I could probably come up with some settings to at least blast annodizing of aluminum. We make lasers where I work and I am a service tech for them.
To the OP, what brand laser are you using?
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I should have stuck to four fingers in Vegas. :o - marubozo's mom