Scientific American 38, 12.6.1847
In manufactures, his is the most brilliant of all the blues. Neither wood, indigo, copper nor cobalt can approach to it. For a long time its application to woollen dyeing was deemed impossible, as a basis of iron was considered to be necessary to the formation of the color; but by late discoveries new combinations of a different nature have resulted in the production of a color of intense brilliancy and very durable without a single grain of iron used as a basis. The process is, for one pound of woollen cloth, two ounces of the prussiate of potass, two of tartaric acid, and equal quantities of nitric acid and sulphuric until the liquor has a slight acid taste. The goods are (any quantity to the above ratio of proportions) put in the boiler after the stuffs are dissolved and gradually brought to a boil and kept boiling for twenty minutes; they are then taken out and washed, and a fresh boiler with a small proportion of logwood and the muriate of tin brought to the boil, through which the goods are run for about 15 minutes. Light blues need not the last process. Cochineal instead of logwood, gives the color an exceedingly rich tinge.