The most useful tool for engraving slate is a hardened-steel pencil.
Slate, regardless of its original color, will always turn white when scratched with the steel pencil. Repeated tracing of the lines will widen and deepen them. It is an ideal way to personalize 4" × 4" slate coasters as gifts.
The pencil is 5 1/2" (14cm) long and 1/4" (6mm) in diameter.