12. CHAPTER XII.
STUDY OF INK.
LACK OF INTEREST AS TO THE COMPOSITION OF INK DURING PART OF THE
EIGHTEENTH CENTURY—THE CONDITIONS WHICH 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,
BEGINS A SCIENTIFIC INVESTIGATION ON THE SUBJECT OF INKS —THE RESULTS
AND HIS CONCLUSIONS PUBLISHED IN 1797—THE ROYAL SOCIETY OF ENGLAND IN
1787 RECEIVES COMPLAINTS ABOUT THE INFERIORITY OF INKS —ITS SECRETARY
READS A PAPER THE SAME YEAR—THE PAPER CITED IN FULL—DR. BOSTOCK IN
1830 COMMUNICATES TO 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 INK ONLY
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 logwood
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.