Laser marking of plastic

I’m having my snapmaker since a few weeks and I’m very happy with it.
I even were successfully in engraving wood, paper and plastic. Furthermore I used the 1.6W laser module for cutting wood and paper.

But now I’m getting stuck with the laser.

I know that plastic materials can be marked with the help of lasers: frothing (getting a light / brown color on dark materials) and carbonization (getting a dark color on bright materials).

For my tests I used a light gray (RAL 7035) PS plastic plate and a black ABS plastic plate.
I’ve played with the power and speed parameters for a long time but I couldn’t generate any laser marking. Either nothing happens or the plastic get engraved.

Can anyone give me a hint, how the parameters should be set (fast speed, low power, …)?
Or can the snapmaker laser module not be used for laser marking operations?

Thanks for our help in advance!

i would definitely like some info also as i am a newby and just learningwith my laser i have only been able to engrave on wood and i would like to do some engraving on plastic

I’ve marked several plastic items (mostly 3d printed things from PETG and PLA) with the 1.6W laser. Both black and grey I think I used 100% power @ 1000mm/m. I didn’t get any charring/darkening, just melting the layers together to make it obvious. So maybe 600-800mm/min @ 0.2mm interval with 100% power should be fine if you want darkening of plastic. However, make sure you have proper ventilation. Plastics are hazardous to laser, especially vinyl, which releases chlorine gas which is toxic to you, and can eat the aluminum of the snapmaker.