Blue Printing

Proce of reproducing drawings in which the lines appear white on a blue ground. The drawing is made on partially transparent paper or cloth with very black ink, and this is laid for a few minutes in sunlight on the sensitized paper, which has previously been prepared in a dark room. The action of the light causes chemical changes, and after the paper is washed with water the drawing appears in white lines. One of the formulas for preparing the sensitized paper is as follows: Di olve 14 oz. of red pru iate of potash in 8 oz. of water and keep it in a bottle; di olve 14 oz. of citrate of iron and ammonia in 8 oz. of water and keep it in a separate bottle; pour equal parts of these into an earthen dish, and wash the paper with a sponge soaked in the solution.