Glass is CO2-laser engraved by frosting the surface: the result is a milky white finish, like sandblasting. It is a demanding material where almost every defect comes from too much energy.
Settings: what really matters
Glass is never laser-cut. When engraving, the principle is to micro-fracture the surface: use the minimum energy that whitens, and nothing more. Too much power produces chips, edges that feel rough, and sometimes a crack right through the piece.
Lower the resolution: around 200 DPI the impacts overlap less and the frosting is more even than at 300 DPI, where glass flakes off in scales.
On a glass or bottle the surface is curved: without a rotary, keep engraving to about 30 mm wide, beyond that focus is lost and contrast collapses.
The wet paper trick
The most effective technique is to stick wet newspaper, or damp masking tape, over the area to be engraved. The water carries heat away as you go: frosting becomes even and chipping almost disappears.
The paper must be pressed flat with no air bubbles, damp but not dripping. Peel it off under warm water at the end.
Risks and finishing
Glass can break under thermal stress, sometimes seconds after engraving: wear glasses, do not lean over the piece and be wary of tempered glass, which can shatter completely.
After engraving, brush the surface with a soft toothbrush and a little soap to remove remaining micro-flakes: the frosting becomes noticeably crisper and pleasant to the touch.
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.