第37章
LACK OF INTEREST AS TO THE COMPOSITION OF INK DURINGPART OF THE EIGHTEENTH CENTURY--THE CONDITIONSWHICH THEN PREVAILED NEARLY THE SAME AS THE PRESENT TIME--CHEMISTRY OF INK NOT UNDERSTOOD--THIS LACK OF INFORMATION NOT CONFINED TO ANY PARTICULAR COUNTRY--LEWIS, IN 1765, BEGINSA SCIENTIFIC INVESTIGATION ON THE SUBJECT OF INKS--THE RESULTS AND HIS CONCLUSIONS PUBLISHED IN1797--THE ROYAL SOCIETY OF ENGLAND IN 1787 RECEIVESCOMPLAINTS ABOUT THE INFERIORITY OF INKS--ITS SECRETARY READS A PAPER THE SAME YEAR--THEPAPER CITED IN FULL--DR. BOSTOCK IN 1830 COMMUNICATESTO THE SOCIETY OF ARTS WHAT HE ESTIMATES TO BE THE CAUSES OF IMPERFECTIONS IN INK--ACTION OF THE FRENCH ACADEMY OF SCIENCES--COMPLICATIONS SURROUNDING THE MANUFACTURE OF INKONLY THIRTY-FIVE YEARS AGO.
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 Professer 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.