Various kinds of so-called " liquid slating " have been sold for converting any smooth board or wall into a black-board for school or other purposes. The following give very good results; No. 1 is probably the best, but is somewhat expensive.
1. Take alcohol (95 per cent.), 4 pints; shellac, 8 ounces; lamp-black, 12 drachms; ultramarine blue, 20 drachms; jaow-dered rotten stone, 4 ounces; powdered pumice stone, 6 ounces. First dissolve the shellac in the alcohol, then add the other ingredients, finely powdered, and shake well. To apply the slating, have the surface of the board smooth and perfectly free from grease. Shake well the bottle containing the preparation, pour out a small quantity only into an old tea-cup, and apply it with a new flat varnish brush as rapidly as possible. Keep the bottle well corked, and shake it up every time before pouring out the liquid.
2. Instead of alcohol take a solution of borax in water; dissolve the shellac in this and color with lamp-black.
3. Dilute silicate of soda (water-glass) with an equal bulk of water, and add sufficient lamp-black to color it. The lampblack should be ground with water and a little of the silicate before being added to the rest of the liquid.