-----------------------+-----------+-----------+-----------+----------- -- |Solution 1.|Solution 2.|Solution 3.|Solution 4. -----------------------+-----------+-----------+-----------+----------- Water | 100 | 100 | 100 | 100 Gum arabic | 20 | -- | -- | -- Ammonia-citrate of iron| -- | 50 | -- | -- Ferric chloride | -- | -- | 50 | -- Potassium ferrocyanide | -- | -- | -- | 20 -----------------------+-----------+-----------+-----------+----------- Mix the first three solutions in the following order in the proportions stated:-- Solution 1. 20 parts. Solution 2. 8 " Solution 3. 5 " As soon as the solution, which at first gets thick and cloudy, is clear and thin, it is spread over the surface of well-sized paper, which is then dried in a warm room. The print, which appears yellow on a dark yellow ground, is treated with the developer (solution 4) by means of a brush dipped in the solution. When the image is deep blue in colour, the print is washed in water and then placed in dilute hydrochloric acid (1 part of acid to 10 parts of water) till the ground is quite white. A final washing with water is then necessary. Waterhouse gives the following formula:-- ---------------------+-----------+-----------+-----------+----------- -- |Solution 1.|Solution 2.|Solution 3.|Solution 4. ---------------------+-----------+-----------+-----------+----------- Water | 650 | 150 | -- | 100 Gum arabic | 170 | -- | -- | -- Tartaric acid | -- | 40 | -- | -- Ferric chloride | | | | solution 45° Baumé | -- | -- | 150 | -- Ferrocyanide of | -- | -- | -- | 20 potassium | | | | ---------------------+-----------+-----------+-----------+----------- Solutions 1 and 2 are mixed and No. 3 added gradually with constant stirring. The mixture is left twenty-four hours, and diluted with water to a specific gravity of 1·100. The paper is coated with the solution and used as already directed, being developed in ferrocyanide of potassium solution and washed with water, treated with weak hydrochloric acid, and then finally cleaned from all traces of acid. _Black Lines on a White Ground._--This modification of the ordinary blue print is arrived at with the following formula:--