A mirror is laser engraved from the back: the beam attacks the silvering layer, which disappears where it passes. The design then shows through when seen from the front, with a sharpness that engraving the glass itself cannot match.
Settings: what really matters
CO2 only, around 45% at 1,200 mm/min with a 40 W CO2, artwork mirrored in software since you engrave from the back.
Do not aim to engrave deep: the goal is to remove the protective paint and the silvering, not to bite into the glass. Excess power chips the front face.
300 dpi is enough: beyond that, pulses overlap and the layer peels off in patches instead of disappearing cleanly.
Common thicknesses and pitfalls
Common thicknesses: 3 and 4 mm. Mirror is not laser cut: have it cut to size by a glazier before engraving.
Pitfall: the front face. A mirror laid face down on the bed scratches on the slightest speck of dust. Rest it on a soft cloth or a clean foam sheet.
On some mirrors, a thick protective paint covers the silvering: two passes are then needed, the first removing the paint, the second the silvering.
Risks and finishing
The protective layer releases paint fumes: extraction is mandatory. Glass does not burn, but chips can fly if power is too high: wear eye protection and keep the piece firmly flat.
For finishing, the engraved design can be painted from the back (black, gold) for a solid-engraving effect, then protected with spray varnish. Black adhesive film on the back gives the same result without paint.
Every figure on LaserSettings comes with the machine, the laser source, the material and the thickness it was tested on. A setting published for a 10 W diode says nothing about a 40 W CO2, and a setting for 3 mm says nothing about 6 mm: check those four things before you copy any number.
Settings are confirmed or disputed by the members who reproduce them, so reliability comes from cross-checking rather than popularity. Photos of the result — cut edges, engraving shades, scorching — tell you more than a single number found on a forum.
Whatever the material, treat a published setting as a starting point: run a small power/speed test grid on an offcut, clean the lens, redo the focus, work with fume extraction and air assist, wear glasses rated for your wavelength and never leave the machine unattended.