Slate is the most forgiving material of all: engraving appears bright white on black with instant contrast and almost no way to get it wrong. Perfect for coasters, signs and personalised gifts.
Settings: what really matters
Slate is not laser-cut, only engraved. The beam does not carve the stone, it flakes off a thin surface layer — that micro-flaking is what appears white.
High power at fast speed gives the best white. Unlike wood, a second pass improves nothing: it greys the result by re-burning the dust already released.
Slate is rarely flat. Focus at the centre of the engraved area, not at an edge, otherwise contrast shifts from one side of the piece to the other.
Risks and finishing
No toxic fumes, but very fine mineral dust you should not breathe: keep extraction running and wipe the piece with a cloth rather than blowing on it.
A little mineral oil or wax over the whole piece deepens the black background and makes the white engraving pop dramatically. On a coaster, use a neutral food-safe oil.
Every figure on LaserSettings comes with the machine, the laser source, the material and the thickness it was tested on. A setting published for a 10 W diode says nothing about a 40 W CO2, and a setting for 3 mm says nothing about 6 mm: check those four things before you copy any number.
Settings are confirmed or disputed by the members who reproduce them, so reliability comes from cross-checking rather than popularity. Photos of the result — cut edges, engraving shades, scorching — tell you more than a single number found on a forum.
Whatever the material, treat a published setting as a starting point: run a small power/speed test grid on an offcut, clean the lens, redo the focus, work with fume extraction and air assist, wear glasses rated for your wavelength and never leave the machine unattended.