I picked up some scratch pieces of black polished granite and went testing.
first it didnt went so well but after a while i found out some settings and it got better.
must say they arent as good as the one lasersafe1 posted.
O and this is on a lasertile Tile that i got 2 samples from, also pretty nice effect.
looks a little bit like an aquarell painting.
only minor thing is that the shipping costs from US to NL are higher then the tiles itself
testing and testing what power/speed/height
got better and better
getting allot of samples
and a little acrylic test