A diode laser can’t engrave clear glass directly, but it can engrave mirrors from the back. The laser removes the paint and silver coating behind the glass. Seen from the front, the design appears clear through the mirror.

What you need

A standard glass mirror with a painted back coating (not acrylic mirror)
Safety glasses
Ventilation: the coating smoke is unpleasant
Optional: LED strip for backlighting, or paint for colour fill

Steps

Mirror your design horizontally in the software. You are working from the back, so text must be reversed.
Place the mirror face down on a clean, flat surface on the bed.
Focus on the back coating.
Engrave in fill mode at low-to-moderate power. You only need to remove a thin coating.
Clean the residue with a soft cloth. Some designs need a second pass for full removal.
Check from the front in good light.

Finishing effects

Backlit: mount an LED strip behind the mirror and the design glows.
Colour fill: paint the engraved area from the back and the design shows in colour from the front.
Frosted look: add a light layer of white paint behind the design.

Tips

Run a small test in a corner to find the lowest power that removes the coating fully.
Too much power can crack the glass or scorch the surface.
Shiny surfaces reflect, so keep goggles on.

What you need