Anodised Aluminium-query

[Ian Stewart-Koster]

I managed to pick up a tub full of round keyring or dog-tag blanks, as well as rectangular plaque shapes.
They're black, blue, red & gold.
I was told they were laserable.

I've been experimenting, and the blue lasers beautifully, cleanly and with good contrast. The red & black a bit less so, but OK.
Doubling the power, or halving the speed in engraving made not much difference.

But I can scarcely get a mark on the brassy looking gold one, when i was told it WAS laserable. (Maybe it's too reflective?)
I'm not really bothered, but I figured I'd ask here if anyone has a secret to getting an impression on anodised gold/brass on aluminium plaques?

I'm using our 50w ULS laser.


Thanks!