Examination for determining whether a writing has been done at one time, or added to later, necessitates some acquaintance with the nature and qualities of ink. In the ordinary case the assistance of a chemist is necessary, but an enlarged photograph shows up minute differences with amazing accuracy.

In the majority of instances alterations are made some time after the original has been written, in which case a difference in the shade of the ink will be perceptible, even to the unassisted eye. This is particularly true when the now almost universal blue-black ink is used.

The period required for an addition to become as black as the older writing depends very much upon the character of the paper. If this be smooth and hard, and the writing has not been dried with blotting paper, but allowed to dry naturally and slowly, it will become black much quicker than if the paper be rough and of an absorbent nature.

A fairly reliable test is to touch a thick stroke of the suspected addition with a drop of diluted muriatic acid—as much as will cling to the point of a pin. Apply the drop to the suspected addition and to the older writing at the same moment, and carefully watch the result. The newer writing will become faint and watery, with a bluish tinge almost instantly, but the change will be slower in the case of the older writing, taking ten or even twenty seconds. The longer the period required for the change, the older the writing.

This same acid test is applied to prove whether a writing is in ordinary ink, or has been lithographed or photographed. If the two latter, the acid will have no effect.

On more than one occasion collectors have purchased as original autographs of celebrities which proved to have been lithographed or photographed, but the persons so deceived have generally been inexperienced amateurs.

When the difference between a written and printed signature has been once noticed it is hardly likely that an observant person will be deceived. It is, however, as well to be carefully on guard against this contingency, for modern photography and process printing have been brought to such a degree of imitative perfection that it is easy for a not too keen-eyed person to experience great difficulty in forming an opinion in the absence of the acid test. Fortunately that is infallible.

It must, however, be admitted that up to the present no great success has attended efforts to determine how long an interval has passed between the writing of the original and the suspected addition. Broadly speaking, the most that the expert can hope to gain from an examination of ink under these circumstances are hints, clues and suggestions rather than definite, reliable facts. Fortunately it often occurs that a suggestion so obtained proves of immense value to the trained or careful observer, though it might convey no conviction to others.

As in the case of nearly all deductive reasoning the handwriting expert becomes sensitive to slight suggestions. If called upon, as he sometimes is, to explain to others how and why one of these slight and almost imperceptible signs fit in with his theory, he fails. Therefore the cautious expert, like a good judge, is careful in giving reasons for his judgment only to cite those which are self-evident.

Many an expert has made a poor exhibition in the witness-box by failing to convey to a jury the impression produced on his own mind by a slight piece of evidence, the proper understanding and interpretation of which can only be grasped by those who have learned how to recognize faint signs.

The process of chemically testing inks for the purpose of ascertaining the points mentioned is quite simple, and is distinctly interesting. In a very important case the services of a qualified chemist will probably be requisitioned, but the cost of the necessary material and the time required to make oneself proficient as a capable tester are so slight that even the small fee that would be charged by a chemist is scarcely worth paying.

The materials necessary are a few test tubes, some bottles of lime water, diluted muriatic acid, a solution of nitrate of silver in distilled water, in the proportion of ten grains to the ounce, some camel hair pencils, and clean white blotting and litmus paper. The whole need not cost more than half-a-crown.

The method of using these materials is best illustrated by describing a test often needed by autograph collectors.

A very common method employed by forgers to give an appearance of age to the ink used in spurious old documents is to mix with ordinary ink, muriatic acid, oxalic acid, or binoxalate of potash. The presence of these colouring agents can be detected in the following manner.

In the first place, washing the letter with cold water will make the ink become darker if acid has been used to brown the ink, but the following test will settle the point beyond dispute:

With a camel's-hair brush wash the letter over with warm water. If, as sometimes happens, a sort of paint or coloured indian ink has been used, this will be immediately washed away and disappear, leaving a rusty smudge. If not, apply the litmus paper to the wetted ink, and the presence of acid will be shown in the usual way by the litmus paper changing colour. If genuine, wetting makes no difference.

Next, pour a drop or two of the water from the writing into a test tube from off the letter, add a little distilled water and one or two drops of the nitrate of silver solution.

If muriatic acid has been used to colour the ink, a thick white precipitate will be seen in the tube immediately.

If not, pour a few more drops of the water which has been washed over the writing into a second test tube, add a little distilled water and a few drops of lime water. A white precipitate will be seen in the tube if either oxalic acid or binoxalate of potash has been employed.

In many cases it will be sufficient to place the tip of the tongue to a thick stroke. An unmistakable acid taste will be noticed.

Further and fuller particulars of the methods resorted to by forgers to simulate ancient documents will be given in the chapter on Autographs.

It is sometimes important to know whether a stroke has been made over another, as in the famous case in which the real issue turned on the question whether an apparent alteration in a signature was really a pen-mark made to indicate where the signatory should sign. It was obvious that if the mark was made first the signature would be over it; if, as was suggested, the mark was added in an attempt to alter or touch up the signature, it must have been written over the signature.

In cases of this kind an enlarged photograph leaves no room for doubt. The ink is seen lying over the lower stroke as plainly as a layer of paint in a picture can be seen overlying the stroke beneath.

This is one of those apparently difficult points which become marvellously simple when dealt with in a practical manner.

Pages might be needed to explain what a very simple experiment will reveal at a glance.

Take a word which has been written long enough for the ink to have become dry, and make a stroke across it. For example, make a letter t without the bar, then, after a lapse of an hour or two, add the cross bar. When this is quite dry and has become as dark as the first mark, examine it with a good glass. The ink of the added bar will be seen plainly overlaying the vertical stroke, but any doubt can be promptly removed by taking an enlarged photograph.

Even when the second stroke is added while the ink on the first is still wet the upper stroke can be distinguished, though not so clearly as if the first stroke had been allowed to dry first.

By practising and examining such strokes, the student will soon learn to distinguish important signs which leave no doubt as to which stroke was first made.