CHAPTER XIII
HOW TO DETERMINE AGE OF ANY WRITING
The Different Kinds of Ink Met With--Inks That Darken by Exposure to Sunlight and Air--Introduction of Aniline Colors to Determine the Age of Writings--An Almost Infallible Rule to Follow--To Determine Approximate Age of Ink Possible--The Ammonia System a Sure One--A Question of Great Interest to Bankers and Bank Employes--Thick Inks and Thin Inks--So-called Safety Inks That Are Not Safe--How to Restore Faded Inks--An Infallible Rule--Restoring Faded Writing--Restored by the Silk and Cotton System That Anyone Can Arrange--Danger of Exposing Restored Writing to the Sun.
The inks in common use over the United States at the present time, and for some years past, are not as numerous as one might be led to conclude. They are probably fifteen or at most twenty in all, including the most popular blue, red, magenta, and green inks. But among these there is a notable difference in character. Some are thick, heavy, and glossy, in character, and flow sluggishly from the pen. Few of these become much darker by standing. In this class will be found the copying inks and those in which a large quantity of gums or similar thickening agents are used.
Other inks are pale, limpid, and flow easily from the pen, and this class usually shows a notable darkening by exposure to sunlight and air. It will be unnecessary here to refer more particularly to the intermediate varieties or to discuss their various composition.
It should be, remembered here that in the last twenty years, or since the introduction into general commerce of aniline colors, which Hofmann discovered in 1856, these latter have been employed more and more in writing fluids; not only in mixtures of which they are the principal ingredients, but to a greater or less degree in all inks. Their presence, even in small quantity, in the gallo-tannate of iron and logwood inks can be generally detected by an iridescent and semi-metallic luster.
To assist in determining the ages of writings by one and the same ink, it is to be observed that the older the writing the less soluble it is in dilute ammonia. If the writing be lightly touched with a brush dipped in ten-per-cent ammonia, the later writing will always give up more or less soluble matter to the ammonia before the earlier. In case of inks of different kinds this test is not serviceable, for characters written in logwood ink, for instance, will always give up their soluble material sooner than nutgall inks, even if the last named be later applied. To estimate the age of writing from the amount of bleaching in a given time by hydrochloric or oxalic acid is very precarious, because the thickness of the ink film in a written character is not always the same, and the acid bleaches the thinner layer sooner than the thicker.
The determination of the age of a written paper is a problem difficult of solution. According to F. Carré the age can be approximately determined if the characters written in iron ink are pressed in a copying press and a commercial hydrochloric acid diluted with eleven parts of water is substituted for water; or, if the written characters are treated for some time with this diluted acid.
The explanation is that the ink changes in time, its organic substance disappears little by little, and leaves behind an iron compound, which in part is not attacked even by acids.
An unsized paper is impregnated with the described diluted acid, copied with the press, and a copy from writing eight or ten years old can be obtained as easily as one by means of water from a writing one day old.
A writing thirty years old gives, by this method, a copy hardly legible, and one over sixty years old, a copy hardly visible. In order to protect the paper against the action of the acid, it should be drawn through ammoniacal water.
To determine the exact age of writings by the ink is not easy. The approximate age may be determined with some degree of certainty. If ink-writings are but a few days old, it is easy to distinguish them from other writing years old. But to tell by the ink which of two writings is the older, when one is but two months and the other two years, is, as a rule, impossible.
Where during the progress of a trial a document purporting to be years old is introduced in evidence, and it can be shown that it is but a few days old, having been prepared for the occasion, ordinarily the age of the writing will be comparatively easy of demonstration by the expert. Oxidization will not have set in to any extent, if the ink is very fresh, and this, with a careful watching of the color for any darkening, will determine whether or not the ink is fresh. This ink study should be a question of the utmost interest to bankers and bank employes.
A ten-per-cent solution of ammonia applied to two inks in question will show which is the fresher. The older ink will resist the action of the ammonia longer and give up less soluble matter than the newer writing. Nutgall, and logwood inks, of course, should not be tested comparatively by this method, as the logwood ink will respond to the ammonia sooner than the nutgall ink.
F. Carré also gives another method for determining, approximately, the age of ink-writings. If the writing is in iron ink, and is moistened with a solution of one part of hydrochloric acid to eleven parts of water and put in letter-copying press and copy transferred to copy paper it should give a strong copy, if but ten years old; a hardly legible copy, if thirty years old; and if sixty years old, a few marks will be copied, but they will not be legible.
If the same solution be used in place of water, as in the ordinary letter-copying process and the copying paper be saturated with it, the result will be the same.
To determine the age of writing by applying bleaching acids and watching results and counting the seconds is a dangerous method. Thick inks will respond to the acids slower than thin, and the time comparisons are misleading.
Safety inks, so-called, designed to resist the action of acids and alkalies have been repeatedly put upon the market, but no such ink has ever successfully challenged the world and proved its title of safety.
Many chemicals are recommended as restorations for faded writing, but these should be avoided as far as possible, as they are liable to stain, disfigure the paper, and in the end make matters materially worse. Familiarity with particular handwritings after some practice will enable the reader to make out otherwise unintelligible words without any other assistant than a powerful magnifying glass.
If the ink is very faint, the simplest and most harmless restorative is sulphate of ammonia, but its loathsome smell once encountered is not easily forgotten. The experiment in consequence is very seldom repeated for the result is scarcely good enough to risk a repetition of so horrible a smell.
The writing on old and faded documents may be restored, by chemical treatment, turning the iron salt still remaining into ferrous sulphate. A process which will restore the writing temporarily is as follows: A box four or five inches deep and long and broad enough to hold the document, with a glass, is needed. A net of fine white silk or cotton threads is stretched across the box at about one half the depth. Two saucers containing yellow ammonium hydrosulphide are placed in the bottom of the box. By means of a clean sponge or brush, moisten the paper with distilled water; then place it on the net with the writing side down. The action of the vapor of the ammonium hydrosulphide will cause the obliterated writing to slowly turn brown, then black. But within a short time after removal from the box the writing will again disappear.
Another method is to wash the document carefully in a solution of hydrochloric acid, one part, and distilled water, one hundred parts. Dry the moistened paper somewhat, leaving it just moist enough to hold a uniform layer of fine yellow prussiate of potash. A plate of glass with a light pressure should be placed on this. In a few hours dry the paper thoroughly, and carefully brush off the yellow prussiate of potash. The writing should come out a Prussian blue. This restored writing will be permanent unless exposed too much to the light.
The hydrochloric acid must be thoroughly removed; otherwise, it will destroy the paper. Crystallized soda, two parts, and distilled water, one hundred parts, in solution, will counteract the hydrochloric acid, if the document is allowed to float on it for twenty-four hours.