For permanent writing on slate chalkboards we recommend our edding 4000 matt paint markers and edding 4040 matt paint markers. These pens are ideal for semi-matt designs on dark and particularly porous surfaces. Their paint-like, opaque ink is water-based and odour-free, as well as being weatherproof and extremely lightfast.
If you want to be able to wipe the writing off a slate chalkboard then we recommend our chalk markers, such as the edding 4090 or the edding 4095. If the surface of your chalkboard is smooth and non-porous, you should be able to wipe off the writing easily with a damp cloth.
Both our matt paint markers and our chalk markers operate with a pump system, so you need to shake them well before use. After shaking, remove the cap and pump the marker until ink appears in the nib.