In the decoration of schools, and sometimes in that of nurseries in private houses, the painter may be asked to treat blackboards or sections of the wall surface which can be used in this capacity.
Most paint manufacturers will supply ready-mixed blackboard slating for this purpose, not only in black but also in dark blue, dark green, and other colours which, it is claimed by some authorities, are less trying to the eyes than black. The surface should be prepared, primed, and under-coated in the usual way and the slating applied on top.
Many decorators prefer to make up their own blackboard composition, and though it is not difficult to do so, some care is necessary to produce a finish which will give a film with just sufficient ‘ bite ‘ to hold the chalk marks without retaining too much and thus making them difficult to wipe off. Quite an effective mixture, to yield a dark-blue slating, can be made by taking the following:
Before applying, stir well together and apply quickly with a flat brush. Should it be found that the coating, after it has dried on the surface, is rather too rough to permit easy cleaning, wash well and flat down with fine-grade abrasive paper.