How to engrave slate with a diode laser: settings and technique guide

Slate is one of the most satisfying materials to laser engrave. You do not need any coating or treatment — the laser ablates the dark surface and reveals a lighter grey or white layer beneath. The result looks clean, permanent, and professional.

Diode lasers engrave slate well at 445nm wavelength. You cannot cut slate with a laser — the stone is too dense — but engraving works across the full power range from 10W diodes upward.

Surface preparation

Wipe the slate surface with a damp cloth and let it dry completely before engraving. Dust or grit on the surface can scatter the beam and cause uneven marks. Some makers apply a thin coat of dish soap to the surface and let it dry, which can improve contrast — the soap residue changes how the surface ablates. Worth testing on a scrap piece.

Slate coasters and tiles vary in surface flatness. Run your finger across the surface before placing it in the laser. If there is significant variation in height, shim the lower corners with a piece of card to level it. The focal distance affects engrave quality more on stone than on wood because there is no material compression to absorb minor focus error.

Settings for slate coasters

Getting white contrast vs grey contrast

The brightness of the engraved mark depends on depth of ablation. More power or slower speed removes more material and produces brighter marks. But too much power creates a rough, cratered surface that looks blown out rather than clean.

Start at the settings above and run a test square. If the result looks grey rather than white, increase power by 5% or decrease speed by 10%. If the surface looks rough or spalled, reduce power. The target is clean ablation that reveals the lighter stone layer without fracturing it.

Image settings: photo vs line art

For photograph engraving on slate, use grayscale mode in LightBurn with Jarvis or Newsprint dithering. These dither algorithms produce dots that read as continuous tone from a normal viewing distance. Threshold (pure black/white) works well for logos and text but loses mid-tone detail in photos.

Line art and text engrave crisply on slate at any DPI above 200. 254 DPI is a good default. There is no benefit to running higher DPI on slate for simple vector designs — the stone surface cannot resolve the extra detail.

Cleaning after engraving

After engraving, there will be dust on the surface — ablated stone particles that look like white powder. Wipe with a damp cloth or use compressed air to blow it off. The engraved marks are permanent; the powder is just residue from the process.

Some makers apply a light coat of oil to the finished piece. Baby oil, mineral oil, or a beeswax polish darkens the un-engraved slate and increases the contrast of the engraved marks. Apply a thin coat, let it absorb for a few minutes, then buff off the excess. The result looks more polished and shows off the design better.