The short answer
Use greyscale when the material darkens gradually with power — many woods and coated materials do — and when your controller modulates power cleanly at the speed you engrave. Use dithering when the material is essentially binary, when your controller cannot modulate power reliably, or when you want a predictable, repeatable structure. On materials like anodised aluminium or slate, where the mark is either there or not, dithering usually looks better than a greyscale ramp that the material cannot express.
- Material reacts gradually to power → greyscale is worth trying
- Material marks or does not mark → dithering
- Unsure about your controller → dithering is the safe default









