CO2 engraving
Surface micro-fracture
Operator
Tempered glass
A CO2 laser engraves and frosts glass well and cannot cut it. The beam heats the surface so fast that a very thin layer fractures into microscopic cracks; those cracks scatter light, which is the white frosted look. Because the mechanism is controlled surface damage, it stays a surface process — driving it deeper just cracks the piece. The two things that separate a good result from a bad one are using less energy than instinct suggests and keeping the surface cool, commonly with a damp paper towel. And one absolute: never put tempered glass in a laser.
1 · What’s happening at the surface.
Glass doesn’t vaporise cleanly, and it doesn’t melt into a manageable pool at these energies. What it does is fracture. The beam dumps energy into a very thin surface layer far faster than the glass can conduct it away, and the resulting thermal stress shatters that layer into a mass of tiny cracks.
Those micro-fractures scatter light instead of transmitting it, which reads as white frost. So a good engraving is many small, evenly distributed fractures, and a bad one is fewer, larger fractures — chips, flakes and a rough patchy surface. Almost every technique below is about pushing toward the first outcome.
2 · Why it can’t cut.
Two properties work against a through-cut, and they compound:
- Brittleness — glass relieves stress by cracking, and a crack goes where the material’s flaws send it, not where you programmed.
- Poor thermal conductivity — heat concentrates instead of spreading, so stress builds steeply right where the beam is.
Push for depth and you get an uncontrolled crack through the piece. That’s controlled-fracture territory, and the controlled version of it is a genuine specialist process rather than something a shop CO2 does. Controlled-fracture cutting →
Cutting glass practically means scoring and snapping, waterjet, or a purpose-built process — not a shop laser.
3 · Getting an even frost.
| Technique | Why it helps |
|---|---|
| Lower power, higher speed | Many small fractures instead of a few large ones — the single biggest lever |
| Damp paper towel on the surface | Draws heat away and evens the result; a widely used shop trick. Keep it flat and wrinkle-free |
| Thin film of dish soap | Same idea — a sacrificial heat-spreading layer |
| Higher resolution / dot patterns | Distributes energy more evenly than solid raster fills |
| Slight defocus | Spreads energy over a marginally larger spot, reducing local intensity |
| Clean the surface first | Residue and fingerprints cause uneven absorption and blotchy marks |
Curved surfaces — bottles, glassware — need a rotary attachment to keep the surface at a consistent distance, since focus varies across a curve.
4 · Tempered glass — the hard no.
Never laser tempered glass
Tempered (toughened) glass is manufactured with built-in internal stress — that’s what makes it strong and makes it crumble into blunt fragments when it fails. Disturbing the surface can release that stress, and the entire panel can shatter, potentially during the job or afterwards.
This applies to oven doors, shower panels, phone screens, car glass, many architectural panels and plenty of drinkware. If a piece is not confirmed annealed, treat it as tempered and don’t run it. The failure mode isn’t a spoiled part — it’s a panel letting go.
5 · What glass work suits a laser.
Awards and trophies, personalised drinkware and bottles, signage and door panels, decorative panels, and scientific or measurement markings on labware. All of it is surface work, which is exactly what the process is good at.
For fine, low-heat marking on glass — and for consistency on demanding work — a UV laser is the specialist tool, working at a much shorter wavelength with far less thermal stress.
6 · FAQs
Frequently asked
GlassQCan a laser cut glass?
Not practically. It engraves and frosts the surface well, but glass is brittle and a poor heat conductor, so trying to cut through causes uncontrolled cracking. Use scoring and snapping, waterjet, or a specialist process.
QHow does glass engraving work?
The beam heats a very thin surface layer so fast that it fractures into microscopic cracks, which scatter light and appear white. It’s controlled surface damage rather than material removal.
QWhy does mine look chipped?
Too much energy in one spot — you’re making a few big fractures instead of many small ones. Lower power, higher speed, higher resolution, and a damp paper towel on the surface.
QCan you engrave tempered glass?
No. It’s under built-in internal stress and disturbing the surface can shatter the whole panel. If it isn’t confirmed annealed, don’t run it.
7 · Related in this series.
Part of Materials & Safety:
- Controlled-fracture cutting — the physics behind this
- Anodized aluminum — the other surface-only job
- What must never go in a laser
Keep exploring
One idea leads to the next.
Knowing how a material behaves under the beam is most of the job. Follow the rest of the series, or talk it through with someone who runs these systems.