Buy extract of logwood, which may be had at three cents an ounce, or cheaper by the quantity. Buy also, for three cents, an ounce of bi-chromate of potash. Do not make a mistake, and get the simple chromate of potash. The former is orange red, and the latter clear yellow. Now, take half an ounce of extract of logwood and ten grains of bi-chromate of potash, and dissolve them in a quart of hot rain water. When cold, pour it into a glass bottle, and leave it uncorked for a week or two. Exposure to the air is indispensable. The ink is then made, and has cost five to ten minutes' labor, and about three cents, beside the bottle. The ink is at first an intense steel blue, but becomes quite black.