Scientific American 1, 13.9.1856
The sulphate of indigo (chymic) is used in great quantities for coloring silk and woolen goods, and fine sheepskins. It is the principal coloring ingredient for light blues and greens. It is made by dissolving finely pulverized indigo in pure strong sulphuric acid. The very best of indigo is required for its manufacture because inferior indigo requires more sulphuric acid while it gives out far less coloring matter thereby involving a loss of material in condition with an inferior product. All indigo contains more or less lime; but the inferior kind the most; this the reason why it takes up more sulphuric acid to manufacture an inferior chymic.
At the present moment, and for the past two years, the sapply of the first quality of indigo has not been equal to the demand for it, and that demand is constantly increasing. Some very excellent indigo, well adapted for making chymic, used to be obtained from Guatemala, but the kind most esteemed is the first quality of Bengal, for which we are dependent on a colony of Great Britain.— About twelve years ago, the best Bengal indigo could easily be obtained, but at present it is almost unknown in the market. A spurious article, however, much resembling it, is abundent, but it does not possess one half the coloring matter of the genuine, and yet it is sold at a retail price varying from six to fourteen shillings per pound.
Our object is to direct the attention of our southern planters to the cultivation of the indigo plant, and the manufacture of the best kinds of indigo, for inferior kinds are by far too plentiful.
About sixty years ago—and within that period-some a very fine qualities of indigo used to be cultivated in South Carolina; its character was much higher than the finest Guatemala or the best Bengal, but it is now unknown in the arts, to the great regret of calico printers, dyers, and leather dressers.—In the ferment ration of the indigo plant so much oxygen is absorbed that its manufacture was found to be very injurious to the health of the negroes on the plantations; this was one reason for giving up its culture; and another, and perhaps the strongest, was the higher profits derived from the cultivation of cotton. It appears to us now, however, that with the curds a of sufficient care, the health of the negroes may be maintained as well as in the rice culture: also that the price which could now be obtained for it would be very remunerative. There are hundreds of persons in our country who would rather pay two dollars per pound for the best kind of indigo - that quality which was manufactured at one time in South Carolina or the kind that was sold for the best Bengal twelve years ago — than that which is now sold for seventy-five cents per pound. We think these considerations ought to induce some of our planters to engage in the cultivation of the finest qualities of indigo.
Since our planters have best all the efforts of the East India Company to rival them in the cultivation of cotton, it appears to us that their honor is somewhat at stake to regain their lost reputation in the cultivation of indigo.