Manufacturer and builder 5, 1876
The following is suggested by Böttger for dyeing cotton a pure blue: Heat a mixture of 187 grains of Prussian blue, 187 grains of tartaric acid, ½ fluid ounce of ammonia water, and 2½ fluid ounces of water, and filter after cooling. Add to the deep blue filtrate gradually a solution of caustic soda, until it is decolorized, and after some time assumes a light yellow tint. Impregnate the cotton with this solution, and pass it (preferable after allowing it to dry) through a warm, very dilute solution of sulphuric acid. This will neutralize the caustic soda, which discolored the Prussian blue, forming the soluble and neutral sulphate of soda, and the cotton will immediately assume a beautiful blue color, and needs only to be washed in water. The sulphuric acid must be so diluted that it has only a slightly perceptible sour taste.