It was used alone as an ink long before, as well as contemporaneously with, those of the tanno-gallate of iron family. Its lasting properties are most remarkable if it be true that, used as a dye, there is still in existence specimens of it on cloth five thousand or more years old. The history of its use ALONE as an ink is difficult to ascertain back of a certain period;the writer has several specimens of it, one written in 1692 whose color is a green blue; another written about a century ago is believed to be as bright blue as the day it was placed on the paper; from 1810 to 1850 it was in common use particularly in hot climates where it was "home-made." Consequently if the old "gall" inks contained a lasting added color, indigo must have been the one, Dr. Stark whose investigations along this line for twenty-three years have already been cited has said that he preferred for his own use an ink composed of galls, sulphate of indigo and copperas (sulphate of iron);this means a tanno-gallate of iron ink with indigo for "added" color. Like formulas calling for different proportions of constituents both before and after his time in England and the continents of Europe and America are to be found in considerable number, proving that its use was more or less constant in this respect. To determine, then, whether or not the blacker specimens of the ancient writings contained indigo in any of its forms was most important, and the plan adopted most simple. Specimens of writing in ink of which the manufacturer's name was known as well as his formula and only thirty years old showed evidence of considerable "browning;" some of them when tested in juxtaposition with those of from fifty to one hundred years old which had turned completely brown, gave approximately the same results, and differentiated largely from the results obtained from jet black specimens of eighty to five hundred or more years of age. In a number of the browner ones indigo was found to be present while in many of the black ones it was not, demonstrating that the reason for the continuing blackness of the older inks is not due to an added color or pigment of any kind and furthermore that the "Stark" and corresponding ink formulas after the test of TIME did not retain their original blackness but deteriorated to a brown color; moreover, that their purpose as in the present day was to give an agreeable and immediate color result, a free-flowing ink, and to cheapen the cost of manufacture when compared with that of an unadulterated tanno-gallate of iron ink.
No disagreement being now possible as to the lasting color virtues of a properly proportioned tanno-gallate of iron ink WITHOUT an "added" color or pigment, there remained the sole question as to the vehicle utilized to hold this combination in suspension and whether or not it had to do with the continuing blackness of the older inks.
The answer must lie between the vegetable product known as gum and the animal product known as gelatine. The first disintegrates, quickly absorbs moisture and gradually disappears, while gelatine (isinglass) "contains under conditions 50% carbon, although its molecular formula has not yet been determined. It cannot be converted into vapor and does not form well-defined compounds with other bodies; it is insoluble in alcohol which precipitates it in flakes from its aqueous solution. It is also precipitated by tannin, which combines with it to form an insoluble non-putrescible compound. Gallic acid, however, does not precipitate it." (Bloxam.)Possessing an undisturbed and complete history it was the very substance employed long before the discovery of gall ink, and is found present in the earliest specimens of the "Indian" inks which remain to us.
It must now be evident that there can be no material difference of opinions as to what has been so clearly and conclusively established, viz. that ink which contains a base of tanno-gallate of iron (without "added" color) is a permanent ink, and the length of its durability and continuing pristineness can be disturbed only by inferior quality of constituents, wrong methods of admixture and its future environment. Hence any black ink with this combination missing is of no practical value whatever either for record or commercial uses.
"Indian" ink, except for specific purposes, belongs to the great past and will so continue with its virtues unchallenged and proven, until some solvent is discovered for the carbon which forms nearly the whole of its composition, at which time THE perfect ink can be said to have been discovered.
