Study of Ink

[This is taken from David N. Carvalho's Forty Centuries of Ink, originally published in 1904.]


THE increasing demands for ink, and the lack of interest as to its composition during the eighteenth century, if viewed in the same lights which prevail in our own times, permitted the general manufacture of cheap grades of ink which possessed no very lasting qualities. The chemistry of Inks was not fully understood, indeed we find Professor Turner of the College of Edinburgh declaring in 1827:

“Gallic acid was discovered by Scheele in 1786, and exists ready formed in the bark of many trees, and in gall-nuts. It is always associated with tannin, a substance to which it is allied in a manner hitherto unexplained. It is distinguished from tannin by causing no precipitate in a solution of gelatine. With a salt of iron it forms a dark blue coloured compound, which is the basis of ink. The finest colour is procured when the peroxide and protoxide of iron are mixed together. This character distinguishes gallic acid from every other substance excepting tannin.”

The general lack of information or knowledge respecting ink chemistry or its time-phenomena was not confined to any particular country, and it does not appear that any general or specific attention was scientifically directed to it until 1765, when William Lewis, F. R. S., an English chemist, publicly announced that he proposed to investigate the subject.  His experimentations covered a period of many years and their results and his theories as to the phenomena of inks were published in 1797. The most valuable of his conclusions were that an excess of iron salt in the ink is detrimental to color permanence (such ink becoming brown on exposure) and also that acetic acid in the menstruum provides an ink of greater body and blackness than sulphuric acid does (a circumstance due to the smaller resistance of acetic acid to the formation of iron gallo-tannate). Many of his other observations were later shown to have been erroneous. Dr. Lewis was the first to advocate log-wood as a tinctorial agent in connection with iron and gall compositions.

Ribaucourt, a French ink maker, in 1798 determined that an excess of galls is quite as injurious to the permanence of ink as an excess of iron.

Pending the completion of the researches of Lewis, the Royal Society of England, affected by complaints from all quarters relative to the inferiority of inks as compared with those of earlier times, brought the subject to the attention of many of its members for discussion and advice. Its secretary, Charles Blagden, M. D., read a paper before the society, June 28, 1787, which was published in the “Philosophical Transactions” and widely circulated. It is so interesting that copious extracts are given:

“In a conversation some time ago with my friend Thomas Astle, Esq., F. R. S. and A. S., relative to the legibility of ancient MSS. a question arose, whether the inks in use eight or ten centuries ago, which are often found to have preserved their colour remarkably well, were made of different materials from those employed in later times, of which many are already become so pale as scarcely to be read.  With a view to the decision of this question, Mr. Astle obligingly furnished me with several MSS., on parchment and vellum, from the ninth to the fifteenth centuries inclusively, some of which were still black, and others of different shades of colour, from a deep yellowish brown to a very pale yellow, in some parts so faint as to be scarcely visible. On all of these I made experiments with the chemical re-agents which appeared to me best adapted to the purpose, namely, alkalis both simple and phlogisticated, the mineral acids, and infusions of galls.

“It would be tedious and superfluous to enter into a detail of the particular experiments, as all of them, one instance only excepted, agreed in the general result, to shew that the ink employed anciently, as far as the above-mentioned MSS.  extended, was of the same nature as the present; for the letters turned of a reddish or yellow brown with alkalis, became pale, and were at length obliterated, with the dilute mineral acids, and the drop of acid liquor which had extracted a letter, changed to a deep blue or green on the addition of a drop of phlogisticated alkali; moreover, the letters acquired a deeper tinge with the infusion of galls, in some cases more, in others less. Hence it is evident, that one of the ingredients was iron, which there is no reason to doubt was joined with the vitriolic acid; and the colour of the more perfect MSS. which in some was deep black, and in others purplish black, together with the restitution of that colour, in those which had lost it, by the infusion of galls, sufficiently proved that another of the ingredients was a stringent matter, which from history appears to be that of galls. No trace of a black pigment of any sort was discovered, the drop of acid which had completely extracted a letter, appearing of an uniform pale ferrugineous color, without an atom of black powder, or other extraneous matter, floating in it.

“As to the durability of the more ancient inks, it seemed, from what occurred to me in these experiments, to depend very much on a better preparation of the material upon which the writing was made, namely, the parchment or vellum; the blackest letters being those which had sunk into it deepest. Some degree of effervescence was commonly to be perceived when the acids came into contact with the surface of these old vellums. I was led, however, to suspect, that the more modern; for in general the tinge of colour, produced by the phlogisticated alkali in the acid laid upon them, seemed less deep; which, however, might depend in part upon the length of time they have been kept: and perhaps more gum was used in them, or possible they were washed over with some kind of varnish, though not such as gave gloss.

“One of the specimens sent me by Mr. Astle, of the fifteenth century, and the letters were those of an engrossing hand, angular, without any FINE strokes, broad and very black. On this none of the above-mentioned re-agents produced any considerable effect; most of them seemed to make the letters blacker, probably by cleaning the surface; and the acids, after having been rubbed strongly on the letters, did not strike any deeper tinge with the phlogisticated alkali. Nothing had a sensible effect toward obliterating these letters but what took off part of the surface of the vellum, when small rolls, as of a dirty matter, were to be perceived. It is therefore unquestionable, that no iron was used in this ink; and from its resistance to the chemical solvents, as well as a certain clotted appearance in the letters when examined closely, and in some places a slight degree of gloss, I have little doubt but they were formed with a composition of a black, sooty or carbonaceous powder and oil, probably something like our present printer’s ink, and am not without suspicion that they were actually printed (a subsequent examination of a larger portion of this supposed MSS. has shown that it is really a part of a very ancient printed book).

“Whilst I was considering of the experiments to be made, in order to ascertain the composition of ancient inks, it occurred to me that perhaps one of the best methods of restoring legibility to decayed writing might be to join phlogisticated alkali with the remaining calx of iron, because, as the quantity of precipitate formed by these two substances very much exceeds that of the iron alone, the bulk of the colouring matter would thereby be greatly augmented. M. Bergman was of opinion that the blue precipitate contains only between a fifth and a sixth part of its weight of iron, and though subsequent experiments tend to show that, in some cases at least, the proportion of iron is much greater, yet upon the whole it is certainly true, that if the iron left by the stroke of a pen were joined to the colouring matter of phlogisticated alkali, the quantity of Prussian blue thence resulting would be much greater than the quantity of black matter originally contained in the ink deposited by the pen, though perhaps the body of colour might not be equally augmented. To bring the idea to the test, I made a few experiments as follows:

“The phlogisticated alkali was rubbed upon the bare writing in different quantities, but in general with little effect. In a few instances, however, it gave a bluish tinge to the letters, and increased their intensity, probably where something of an acid nature had contributed to the diminution of their colour.

“Reflecting that when phlogisticated alkali forms its blue precipitate with iron the metal is first usually dissolved in an acid, I was next induced to try the effect of adding a dilute mineral acid to writing besides the alkali. This answered fully to my expectations, the letters changing very speedily to a deep blue colour, of great beauty and intensity.

“It seems of little consequence as to the strength of colour obtained, whether the writing be first wetted with the acid, and then the phlogisticated alkali be touched upon it, or whether the process be inverted, beginning with the alkali; but on another account I think the latter way preferable. For the principal inconvenience which occurs in the proposed method of restoring MSS. is, that the colour frequently spreads, and so much blots the parchment as to detract greatly from the legibility; now this appears to happen in a less degree when the alkali is put on first, and the dilute acid is added upon it.

“The method I have hitherto found to answer best has been to spread the alkali thin with a feather or a bit of stick cut to a blunt point, though the alkali has occasioned no sensible change of colour, yet the moment that the acid comes upon it, every trace of a letter turns at once to a fine blue, which soon acquires its full intensity, and is beyond comparison stronger than the colour of the original trace had been. If now the corner of a bit of blotting paper be carefully and dexterously applied near the letters, in order to suck up the superfluous liquor, the staining of the parchment may be in a great measure avoided: for it is this superfluous liquor which absorbing part of the colouring matter from the letters becomes a dye to whatever it touches.  Care must be taken not to bring the blotting paper in contact with the letters, because the colouring matter is soft whilst wet, and may easily be rubbed off. The acid I have chiefly employed has been the marine; but both the vitriolic and nitrous succeed very well. They should undoubtedly be so far diluted as not to be in danger of corroding the parchment, after which the degree of strength does not seem to be a matter of much nicety.

“The method now commonly practiced to restore old writings, is by wetting them with an infusion of galls in white wine.”

(See a complicated process for the preparation of such a liquor in Caneparius De Atramentis, A. D.  1660, p. 277)

“This certainly has a great effect; but is subject, in some degree, to the same inconvenience as the phlogisticated alkali, of staining the substance on which the writing was made. Perhaps if, instead of galls themselves, the peculiar acid of or other matter which strikes the black with iron were separated from the simple astringent matter, for which purpose two different processes are given by Piesenbring and by Scheele, this inconvenience might be avoided. It is not improbable, likewise, that a phlogisticated alkali might be prepared better suited to this object than the common; as by rendering it as free as possible from iron, diluting it to a certain degree, or substituting the volatile alkali for the fixed. Experiment would most likely point out many other means of improving the process described above; but in its present state I hope it may be of some use, as it not only brings out a prodigious body of colour upon letters which were before so pale as to be almost invisible, but has the further advantages over the infusions of galls, that it produces its effect immediately, and can be confined to these letters only for which such assistance is wanted.”

The Society of Arts in 1830, received a communication from Dr. Bostock, in the course of which he stated that the “tannin, mucilage and extractive matter are without doubt the principal causes of the difficulty which is encountered in the formation of a perfect and durable ink and for a good ink the essential ingredients are gallic acid and a sesqui salt of iron.” Owing to his working with galls he was unable to make decisive experiments, but he concludes, and that rightly, that in proportion as ink consists merely of gallate of iron, it is less liable to decomposition and any kind of metamorphosis.

In 1831 the Academy of Sciences in France took up the matter and designated a committee composed of chemists with instructions to study the subject of a permanent ink. After long research it reported that it was unable to recommend any better ink than the tanno-gallate of iron one then in use, but “it should be properly compounded.”

Peddington investigated, 1841-48, the ancient MSS.  collected by the Asiatic Society of Bengal, Calcutta, and published the results in “Examination of Some Decayed Oriental Works in the Library of the Asiatic Society,” which are of much interest as relating to “mineral” inks, the “gall” inks being unknown in Asia after the twelfth century.

Up to thirty-five years ago, the manufacture of “gall” inks necessitated a complicated series of processes and long periods of time to enable the ink to settle properly, etc. It was Professor Penny of the Anderson University who suggested the way to avoid one of the processes pertaining to ink-making by utilizing the known fact, that tannin is more soluble in cold than in warm or hot water. It was adopted all over the world and revolutionized the manufacture of ink, by doing away with boiling processes and hot macerations of ingredients. With hardly in exception the best tanno-gallate of iron (“gall”) inks are now “cold” made.



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