Spanish white, which is simply very fine chalk, is mixed with water and just enough flour paste to cause the particles to adhere when dry. If too much paste is used, the crayons will he too hard and will not mark well; if too soft, they will crumble. The proper proportions should be found by experiment, as different qualities of flour possess different adhesive properties. The wet chalk may be formed into proper shape by means of paper moulds, or it may be rolled out to the required shape and cut into suitable lengths.
For making drawings of objects of natural history, etc., it is frequenely desirable to use colored crayons, the most useful colors being green, red and yellow. A little cheap, dry paint mixed with the chalk will give the desired tints.
Crayons which are not too hard to make a good clear mark, are very apt to be brittle and unable to stand any pressure on the point when they are of sufficient length to be handled easily. If the crayons are made true cylinders, they may be covered with paper, which will serve the same purpose as the wood in the common lead pencil, and may be cut away as wanted. The common crayons, being conical, are not so easily covered, but may, nevertheless, be wrapped with a long, narrow slip of paper so as to be strong and durable.