Laser engraving glass, stone and slate: no cracks, no frustration
are explained briefly when you hover over or tap them.
Glass, stone and ceramic cannot be cut, but they engrave very nicely. The laser melts or blasts off tiny parts of the surface, producing a matt, light contrast. Whether this works depends heavily on the laser type: what almost always works with CO₂ often needs a trick with a diode laser.
Overview
| Material | CO₂ | Diode | Result |
|---|---|---|---|
| Clear glass | good | only with a coating | matt, milky white |
| Dark or coloured glass | good | partly, test it | matt |
| Mirror (back) | good | good | mirror layer is removed |
| Slate | very good | very good | light grey on dark |
| Granite, dark polished | good | good | light on dark |
| Granite, light | limited | limited | little contrast |
| Marble | good | possible | light, depending on the stone |
| Tiles, glazed | good | depends on colour, often with a coating | glaze becomes matt or is removed |
Glass
With a CO₂ laser: glass absorbs the 10,600 nm wavelength well. The surface heats up abruptly and tiny splinters flake off. This gives the typical frosted look, like sandblasting. Deep engravings are not the aim; the effect comes purely from the rough surface.
The main problem is heat. Too much energy in one spot leads to cracks, chipping and a coarse-grained engraving. In its glass tips, Epilog recommends two simple aids:
- Damp paper: lay a dampened piece of newspaper or kitchen paper flat on the engraving area. It cools and spreads the heat, and the engraving becomes more even.
- Washing-up liquid: a thin layer of ordinary washing-up liquid keeps the surface moist. On longer jobs it dries out and has to be renewed.
A few further rules: keep the power rather low, choose a suitable resolution rather than the maximum, and engrave filled motifs with a raster pattern (dithering) rather than a full fill. It is also important to get the setting right on the first attempt. According to Epilog, repeating a job on glass several times produces an increasingly blurred engraving. So test on an offcut of the same glass.
With a diode laser: clear glass lets the blue light at around 450 nm pass almost completely. Without help, nothing happens. The usual approach is a dark coating: black tempera paint, a thin matt spray paint or a laser marking spray. The layer absorbs the energy, heats the glass surface and creates fine cracks there. Afterwards you wash the paint off. The result is usually weaker and less even than with CO₂, but usable for one-offs. Dark and coloured glass sometimes works without a coating too; you have to test that.
For round glasses and bottles you need a rotary attachment. For internal engravings in crystal glass there are dedicated UV laser machines, such as the xTool F2 Ultra UV.
Mirrors
With mirrors you engrave the back. There, a protective paint layer sits over the mirror layer. The laser removes the paint and the mirror layer, and from the front you see the motif through the glass. Mirror the motif beforehand, otherwise lettering is reversed.
Start with low power and work up, because the layer thickness differs depending on the manufacturer. This works well with both diode and CO₂, because the dark paint on the back absorbs the light. The front of a mirror, by contrast, is unsuitable for diode lasers.
Slate
Slate is one of the most rewarding materials of all. The laser lightens the dark surface, producing a light grey, very legible contrast. This takes little energy. As a reference for a 100 W CO₂ laser, Trotec gives only 20 % power at full speed and 500 dpi.
Natural slate is uneven and splits into layers. Dust the surface before lasering and set the focus to the middle height. After engraving, wipe off the dust. A few drops of cooking oil on the surface darken the slate again and increase the contrast. Coasters and signs made of slate are available as ready-made blanks.
Granite and marble
Dark, polished granite gives light, fine engravings. According to Trotec, light granite engraves only to a limited extent. For more contrast, fill the engraving with acrylic paint after lasering and wipe off the excess.
Marble also engraves light. For this, Trotec gives clearly more energy than for slate, with 50 % power at 20 % speed on the same 100 W machine. Trotec also recommends trying a focus distance shifted by about 1 mm up and down, because very hard stones often come out better with a slightly changed focus.
Ceramic and tiles
Glazed tiles and mugs react very differently depending on the glaze. A CO₂ laser frosts or removes the glaze. With diode lasers a lot depends on the colour: dark glazes tend to absorb the blue light, while white and light ones hardly do. For light tiles, many people use a coating of marking spray or paint, similar to glass. Do not rely on dishwasher resistance until you have tested it yourself.
Starting values
A rough guide for your first test grid. Stone and glass differ from piece to piece.
| Material | 10 to 20 W diode | 40 W diode | 40 to 55 W CO₂ |
|---|---|---|---|
| Slate | 30 to 60 %, 100 to 300 mm/s | 20 to 40 %, 200 to 400 mm/s | 15 to 30 %, 300 to 500 mm/s |
| Granite, dark | 60 to 100 %, 80 to 200 mm/s | 50 to 80 %, 150 to 300 mm/s | 40 to 70 %, 150 to 300 mm/s |
| Glass, coated | 60 to 100 %, 80 to 200 mm/s | 50 to 80 %, 150 to 300 mm/s | not needed |
| Glass, uncoated | not suitable | not suitable | 15 to 30 %, 200 to 400 mm/s |
As a calibration start for stone under 60 W laser power, Trotec gives about 100 % power at 15 % speed and tests downwards from there. How to build a grid is covered in Material test.
Safety
Glass can crack during engraving, and small splinters fly. Handle freshly engraved pieces carefully. Lasering stone and ceramic produces fine dust. Vacuum it up rather than blowing it away. With open diode lasers, smooth glass reflects part of the beam back. Always wear safety glasses rated for your laser’s wavelength. More in Laser safety.
Continue with: Material test and Engraving, cutting, marking.