LaserCanvas
Glass, slate and stone: marking what you cannot cut
A laser cannot cut glass, slate or stone. What looks like engraving is thermal shock — the surface fractures microscopically and turns white. Glass wants low power, high speed and a damp covering to spread the heat; slate and stone are far more forgiving and need almost no technique.
Nothing here is being cut or vaporised
On wood the beam burns material away. On glass it does something different: it heats a tiny area so fast that the surface cracks. Those microfractures scatter light, which is why the mark looks white and frosted. You are not removing glass so much as breaking it very precisely.
That explains the whole technique. Anything that makes the heating more uniform gives a smoother frost; anything that concentrates it gives chips and flakes.
Which laser
| Material | CO2 | Blue diode | Notes |
|---|---|---|---|
| Glass | Yes — the usual choice | Poor; passes through clear glass | CO2 is absorbed at the surface, which is what you want |
| Slate | Yes, easily | Yes, easily | Forgiving on both; dark surface, pale mark |
| Stone, marble, granite | Yes | Varies with colour | Darker and denser stone marks with more contrast |
| Ceramic tile | Glazed only | Glazed only | You are marking the glaze, not the body |
Glass, which is the fussy one
Untreated, glass tends to chip: the fracture goes deeper than intended in places and flakes lift off, leaving a rough, sparkly, uneven mark. Three things fix it, and the first is oddly low-tech.
- A damp covering. A sheet of wet newspaper, a damp paper towel or a thin coat of dish soap on the surface spreads and sinks the heat. This is the single biggest improvement, and it costs nothing.
- Low power, high speed, fine interval. You want many gentle fractures, not a few deep ones.
- Defocus very slightly. A marginally larger spot spreads the energy and reduces chipping — one of the few times out-of-focus is the goal.
- Clean the glass, then lay a damp (not dripping) paper towel over the area.
- Run at low power and high speed — roughly engraving settings for anodised aluminium.
- Wipe away residue and inspect under a light. Chipping shows as sparkle rather than even frost.
- If it is rough, go faster and lower, not slower and hotter.
Slate, which is the easy one
Slate is close to the most forgiving material there is. It is dark, it marks pale, contrast is excellent, and it does not chip the way glass does. Coasters and signs are popular for good reason.
- Moderate power, moderate speed. The window of settings that works is wide.
- Thickness varies enormously, and the surface is often uneven — focus to the average height of the area you are marking.
- Natural riven edges mean the surface is not flat; expect tonal variation and design around it rather than fighting it.
- Wipe with a damp cloth afterwards to lift dust from the mark.
Stone and tile
- Marble and granite mark well, with polished dark stone giving the strongest contrast. A polished surface also shows the mark more clearly than a honed one.
- Glazed ceramic tile works because you are marking the glaze. Unglazed terracotta mostly does not.
- Painted tile is a different approach again: spray the tile, engrave through the paint, wash off the rest. Often higher contrast than marking the glaze directly.
Safety, which is different here
These materials do not produce the organic smoke wood does, so it is tempting to think extraction matters less. It does not.
- Fine mineral dust is produced, and stone dust is not something to breathe. Keep extraction running.
- Glass reflects. A polished or mirrored surface can send the beam somewhere unintended, particularly on a CO2. Keep the lid closed.
- Thermal shock breaks things. A thin drinking glass can crack outright. Warm it to room temperature first if it has come from somewhere cold, and expect occasional losses.
Common questions
Can a laser cut glass?
No. A CO2 laser will crack or shatter glass rather than part it, and a diode passes straight through clear glass without depositing energy. What lasers do to glass is surface marking — heating it fast enough to create microfractures that scatter light and look white.
Why is my glass engraving chipped and rough instead of smooth?
Too much energy in too small an area, so the fractures go deeper than intended and flakes lift off. Cover the glass with a damp paper towel to spread and sink the heat, drop the power, raise the speed, and defocus very slightly. Faster and lower, not slower and hotter.
Do I need a rotary attachment for tumblers?
For anything more than a narrow strip, yes. On a flat bed the focus drifts as the surface curves away, so the mark fades toward the edges. A rotary turns the object under a fixed head, keeping the marked surface at a constant distance throughout.
Is slate hard to engrave?
It is one of the easiest materials there is — dark surface, pale mark, strong contrast, and a wide range of settings that all work. The main thing to watch is that slate thickness and surface height vary a lot, so focus to the average height of the area you are marking.