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 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.