Engraving mirror issue

I have been experimenting with engraving mirrors (with the 2.8W laser) and am finding I end up etching the glass vs just burning the mirror finish off.

The pattern ends up looking yellow/brownish in color. When I take a chisel and scrap the mirror finish off around it, that area goes clear, and you can feel where the glass actually feels etched.

I am placing the mirror on a wood board when I am running the MPCNC.

Thoughts on what I might need to do?

Running Laser Etch Software

Speed (I varied from 1000 - 1600 mm/s with no difference)

Laser power 255


I would dial in the speed to make sure the image is as sharp as possible and adjust the laser power. If that doesn’t work it must be a coating on your mirrors.