Forty Centuries of Ink / Or, A chronological narrative concerning ink and its backgrounds, introducing incidental observations and deductions, parallels of time and color phenomena, bibliography, chemistry, poetical effusions, citations, anecdotes and curiosa together with some evidence respecting the evanescent character of most inks of to-day and an epitome of chemico-legal ink.

by David Nunes Carvalho

To confirm the chemical tests which may be employed in the determination of the artificial aging of ink marks, photographs made by permitting light to transmit through the paper and to interfere with its rays by filtering them through a "color" screen containing orange and some green, will indicate the presence of a fugitive substance in the ink, usually the "added" color employed in its manufacture.

The process of bleaching or "removal" of ink marks from paper is frequently employed in the attempted eradication of words or figures and the substitution of others on monetary instruments, commonly called "raising." Its purpose is usually a criminal one and some observations as to the modus operandi and its chemistry are not out of place here.

Ink marks made with a compound consisting of the combination of iron and an infusion of galls or its equivalent (a tanno-gallate of iron ink), as treated with certain chemicals, change from a compound with color to a chemical compound, with no color. Nothing has in fact been absolutely removed or eradicated, but it is a mere change of form, a sort of re-arrangement of the particles, the ingredients which formed the original color being still present, but in such a condition that they are invisible to the eye. A restoration of the invisible ink marks so that they can be observed, becomes possible by the use of chemical reagents and is the reverse of the one of erasure or bleaching, and changes the constituents again into a compound which has color from the one which had none. It does, not, however, reproduce the exact composition originally existing. Such a reagent simply goes to the basis of the material as first used, takes up what was left and reforms the particles sufficiently to make them abundantly recognizable. An apt illustration of these chemical changes of color is found in what is known as the phenolphtalein test solution, which is colored deep purplish-red by alkali hydrates or carbonates, and then by the addition of an acid rendered colorless, to be again reddened by an over- plus of the alkali and so on ad infinitum.

A popular material for the purpose of making chemical erasures is chlorinated lime or soda, which becomes more active by first touching the ink mark to be removed with a one half strength solution of acetic acid; this hastens the liberation of chlorine gas, THE active agent which causes the "bleaching" to take place. Hydrogen peroxide, also a bleaching compound, is less rapid in its action than chlorinate of soda; the same may be said of combinations of oxalic and sulphurous acids.

The most effective re-agent for the restoration of a chemically "bleached" iron ink mark is the sulphide or sulphuret of ammonia (it has several names). This penetrating chemical blackens metals or their salts, whether visible or not, if brought together. It must not be used by direct contact, the best and safest plan being to place a quantity in a small saucer, to be set on the floor of a closed box; to fasten to the box lid the specimen to be operated on; in this way the restoration is due to the fumes of the chemical and a possible danger of destruction of the specimen much lessened, especially if the marks are very light or delicate ones. The restoration of color under particular conditions may also be obtained by treatment with tannic acid, potassium ferro-cyanide (acidulated) or a weak solution of an infusion of galls.

CHAPTER XVIII.

INK CHEMISTRY.

SOME OBSERVATIONS AS TO CHEMICAL EXAMINATION OF INK MARKS BY ALLEN—ERASING OF INKS BY CHEMICAL MEANS—APPROVED CHEMICAL TESTS IN THE ASCERTAINMENT OF INK CONSTITUENTS.

A COMPILATION of the methods of Robertson, W. Thompson (Lord Kelvin), Irvine, Wislar, Hoffman and others, relative to the chemical examination of ink marks, is to be found in "Allen's Commercial Organic Analysis." Their experiments, however, date back many years ago, a few of them before the time of the use of the "anilines" for added color. The so-called "alizarin" ink referred to has now become obsolete. The following is the citation in part:

"In chemico-legal cases it is sometimes of importance to ascertain the nature of the ink used, to compare it with specimens of writing of known history, and to ascertain the relative ages of the writings. A minute inspection should first be made with a magnifying power of about 10 diameters, and any peculiarities of color, lustre, shade, etc., duly noted, and where lines cross each other which lie uppermost. The examination is often facilitated by moistening the paper with benzine or petroleum spirit, whereby it is rendered semi- transparent. The use of alcohol or water is inadmissible.