Glass: Etching, Cutting, Drinkware

Glass is reflective at 10,600nm but absorbs enough to etch a frosted layer when the technique is right. The classic glass-laser problem is micro-fracturing, small cracks that appear shortly after etching. Two prep tricks eliminate it.

The micro-fracture problem

When CO2 hits glass, the surface heats unevenly and contracts as it cools. Micro-fractures form at the edges of the etch, they look fine immediately but multiply over hours/days. The fix: even out the heat absorption with a damp barrier.

Two prep methods (pick one)

Method 1: Damp newspaper / paper towel

1. Cut a piece of newsprint or paper towel slightly larger than the engrave area.
2. Wet it thoroughly, wring lightly so it's damp but not dripping.
3. Press it flat onto the glass surface, smoothing all bubbles.
4. Engrave through the damp paper. The water dissipates heat, preventing fracture.
5. Peel off after, paper comes away with debris.

Result: smooth frosted etch, no micro-fracture, no halo.

Method 2: Dish soap

1. Mix a few drops of dish soap into water (1:5 ratio).
2. Apply a thin film to the glass with a soft cloth.
3. Engrave directly through the soap film.
4. Wipe clean after.

Less mess than damp newspaper but slightly less effective on deep etches.

Settings: glass etching (35-50W RF, 2" lens)

Glass type	Speed	Power	Interval
Bottle glass / wine glass	300 mm/s	30-40%	0.08 mm
Thin window glass	400 mm/s	25-30%	0.08 mm
Pyrex / borosilicate	300 mm/s	35-45%	0.06 mm
Crystal (lead glass)	400 mm/s	20-30%	0.08 mm

Drinkware: wine glasses, whiskey glasses, pints

Cylindrical glass items need a rotary. Steps:

1. Mount on rotary; verify roller diameter and object diameter in Lightburn rotary setup.
2. Apply damp newspaper or soap film to the engrave area.
3. 4" lens (101.6mm focal length) preferred over the standard 2" lens, the wine-glass curve is significant and the longer focal length gives ~2.5× more depth of focus to keep both rim and base in focus. Spot size grows roughly with focal length, so the 4" is dimmer detail in trade for forgiving Z range.
4. Test rotation: 360° rotation should land back where it started.
5. Engrave at lower power than flat glass (curved surface is slightly out of focus at edges).

Cutting glass

CO2 won't reliably cut glass, it micro-fractures unpredictably. Glass cutting uses different methods (waterjet, scoring + breaking). Use the laser only for surface etching.

Mirrors

Engraving the BACK of a mirror produces the iconic "etched mirror" effect, the reflective backing is removed where the laser hits, creating a clear etched pattern visible through the front.

• Settings: 300 mm/s, 25-35% power, single pass on the back side.
• Mirror the design horizontally (since you're working from the back).
• Mask the back BEFORE engraving, protects the rest of the mirror coating from incidental smoke contamination.

Common pitfalls

• Cracked glass after engraving: skipped the damp barrier prep. Always prep glass.
• Yellow/brown halo around etch: power too high. Drop 5% and re-test.
• Patchy etch: uneven film application or dust under the prep layer. Wipe glass first with isopropyl, then apply prep.
• Lost detail at edges of curved drinkware: focal variation. Use 4" lens for more DOF, or split design into multiple Z-zones.