Thumbprint

“ The forged print is not an absolute facsimile of the true print. There is a slight discrepancy. But, in addition to this, the paper bears intrinsic evidence that the thumb-print on it is a forgery."
"We will consider that evidence presently, Dr. Thorndyke. To return to the possibility of forging a finger-print, can you explain to us, without being too technical, by what methods it would be possible to produce such a stamp as you have referred to?" ”

“ The thumb-print of the secretary of the United States treasury, reproduced on the face of greenback, silver certificate and bank note of any series would discourage counterfeiting as nothing else ever has done.
But this thumb-print possibility in commercial papers has its greatest future in the positive identification which either thumb or finger print carries with it. Criminologists all over the world have satisfied themselves of the absolute accuracy of the fingerprint identification. ”

“ Two different-sized prints could hardly be made by the same thumb. Then there is the evidence of the use of appliances. Safe-robbers do not ordinarily provide themselves with inking-slabs and rollers with which to make distinct impressions of their own fingers. Then there is the accidental mark on the print which also exists on the only genuine print that could have been used for the purpose of forgery, which is easily explained on the theory of a forgery, but which is otherwise totally incomprehensible. ”

“ In tracking a criminal by a single impression made by a finger, the lineations in so small a space would require to have been clearly imprinted, and to have what many finger-print patterns have not, some notable or significant characteristics about it. Then, when enlarged by photography into a picture of some thirty inches, the measurements from fixed points in the pattern should correspond with those of the person in custody, on suspicion, and the curves should be shown to concur in all their sinuosities. ”

“ Now, this is an entire mistake. A finger-print is merely a fact—a very important and significant one, I admit—but still a fact, which, like any other fact, requires to be weighed and measured with reference to its evidential value."
"And what do you propose to do first?"
"I shall first satisfy myself that the suspected thumb-print is identical in character with that of Reuben Hornby—of which, however, I have very little doubt, for the finger-print experts may fairly be trusted in their own speciality." ”

“ If grey powder is sprinkled over the spot and then brushed off a distinct impression is seen. If the impression of the fingers is left on something soft, like wax, it is often best to use printers' ink to bring out the ridges and patterns of the finger-marks. And so on for various materials. Quite a science has been built up around finger-prints.
“I wish I had that enlarging camera which I have in my laboratory. However, my ordinary camera will do, for all I want is to preserve a record of these marks, and I can enlarge the photographs later. ”

“ There are, however, certain differences between plate-printing and block-printing which affect the essentials of art. When paper is driven into a line so as to fetch the ink out of it, the line may be of unimaginable fineness, it will print all the same; but when the paper is only pressed upon a raised line, the line must have some appreciable thickness; the wood engraving, therefore, can never—except in a tour de force—be so delicate as plate engraving. Again, not only does plate-printing excel block-printing in delicacy; it excels it also in force and depth. ”

“ There, the ten digits of both hands of all the persons who come to be measured, are impressed with clearness and rapidity, and a very large collection of prints is steadily accumulating, each set being, as we shall see, a sign-manual that differentiates the person who made it, throughout the whole of his life, from all the rest of mankind.
Descriptions are also given of various methods of enlarging a finger print to a convenient size, when it is desired to examine it closely. Photography is the readiest of all ”

“ There are important points connected, with the printing of finger-patterns, especially for legal investigation, which come now to be considered. A human finger, as we have seen, is not, for printing purposes, just like a lithographic stone, a box-wood engraving, or a plate of zinc, steel, or copper. ”

“ The method of printing at the laboratory is to squeeze a drop or so of ink on to the slab, and to work it thoroughly with the roller until a thin and even [Pg 39] layer is spread, just as is done by printers, from one of whom a beginner might well purchase a lesson. The thickness of the layer of ink is tested from time to time by taking a print of a finger, and comparing its clearness and blackness with that of a standard print, hung up for the purpose close at hand. ”

“ Then, without a word, he took an ink-pad from his pocket, slipped the glove upon his right hand, inked the tips of the fingers and pressed them carefully upon a sheet of paper. From an inner pocket, he produced a sheaf of photographs, laid them beside the prints, and carefully compared them. Finally he straightened up and looked at us, his face working.
"Do you know what this does, gentlemen?" he asked, in a voice husky with emotion. "It strikes at the foundation of the whole system of finger-print identification! It renders forever uncertain a method we thought absolutely safe! ”

“ Now, if ten prints are taken, without special precautions, from a single finger, it will probably happen that no two of them are exactly alike; for the finger being a rounded object of which only a small part touches the paper, the impressions produced will show little variations according to the part of the finger by which the print is made. But a stamp such as I have used has a flat surface like that of a printer's type, and, like a type, it always prints the same impression. ”

“ The chances of a single finger-print of very simple design, so to say, being repeated in the case of another person, is not to be ignored, and if the suspected smudge is obscure the evidence ceases to be of much value. ”

“ Many must have heard of some such use of a man's hand; and the correspondence that has taken place has brought to light old instances of the hand, or the nail of a finger, or the teeth in one's mouth, being used to certify a man's act, or a woman's. But these have all been isolated instances. Sir Francis Galton, however, has pointed out [2] that in our own times the engraver Bewick had a fancy for engraving his thumb-mark, with his name attached, as vignettes, or as colophons, in books which he published. ”

“ But just as in some fields the ploughman has perforce had to swerve and veer round some fast embedded boulder or old tree stump, varying his intended pattern, so, too, in our fingers curious divergent lineations are found to occur, and we cannot very well tell the reason why. Coloured patches may be designed like so many pretty wall-paper designs, to enclose these patterns in books on finger-prints, but I, for one, cannot see that they throw any light on their genuine nature and origin. ”

“ On the other hand, a method of identification depending on water ink could never have survived for such strict work as our finger-prints. On the palm of the hand it can give a fairly good impression for such simple [Pg 40] identification as is wanted (say) for passports, because the large creases will obviously be those of the bearer of the passport, or as obviously not. These lines of the palm, so well known in palmistry, are as clear to a man as the shape of his hand, while those on the pads of his own fingers are scarcely noticed even now by one man in a million. ”

“ Plate-printing gives by far the finer and sharper impression, but as there is a perceptible body of ink transferred to the paper from the cut lines, it has been supposed that an impression from plate would be more easily photographed than one from surface where only a film of ink is spread upon the top of the raised lines. But surface-printing being much less sharp and distinct than plate-printing, imperfect copies of notes for which that process is used are the more likely to escape detection. ”

“ The principle of a print made from an engraved wood block is that the projecting parts are covered with a thin film of ink, and when the paper is lightly pressed down upon these lines it picks up the ink from the surface wherever it touches it. In the case of an engraved metal plate, the lines on which are cut in the same way and with a similar graver to that used for white line engraving on wood, the inking and printing is quite different. ”

“ At the present moment any printer, and there are many printers in every town, would, at a small charge, blacken a slab and take the prints effectively, after being warned to use very little ink, as described in Chapter III. The occupation of finger printing would, however, fall more naturally into the hands of photographers, who, in addition to being found everywhere, are peculiarly well suited to it, for, taken as a class, they are naturally gifted with manual dexterity and mechanical ingenuity. ”

“ Photographs are valuable in themselves, and the negatives serve for subsequent enlargements. They are unquestionably accurate, and the labour of making them being mechanical, may be delegated. If the print be in printer’s ink on white paper, the process is straightforward, first of obtaining a negative and afterwards photo-prints from it. The importance of the paper or card used to receive the finger print being quite white, has already been pointed out. An imprint on white crockery-ware is beautifully clear. Some of the photographs may be advantageously printed by the ferro-prussiate process. ”

“ In the first place it is necessary to obtain possession of, or access to, a genuine finger-print. Of this finger-print a photograph is taken, or rather, a photographic negative, which for this purpose requires to be taken on a reversed plate, and the negative is put into a special printing frame, with a plate of gelatine which has been treated with potassium bichromate, and the frame is exposed to light. ”

“ If an inked roller is passed over this relief, or if the relief is pressed lightly on an inked slab, and then pressed on a sheet of paper, a finger-print will be produced which will be absolutely identical with the original, even to the little white spots which mark the orifices of the sweat glands. It will be impossible to discover any difference between the real finger-print and the counterfeit because, in fact, no difference exists. ”

“ See how I adjust it," and I watched him, as, with a delicate thumbscrew, he made the needle-like points of the finder coincide with the outside lines of the whorl. "Now here is a photograph from the other robe, also showing the thumb," and he applied the machine carefully to it. "It also is a double whorl of fourteen lines, and you see the angles are the same. And here is the print of the right thumb which your client made for me." He applied the micrometer and drew back that I might see for myself.
"But these photographs are enlarged," I objected.
"That makes no difference. ”

“ A tep-sai of Bengal. A finger-print. Bengal.
The common way for illiterates to sign is to wet the tip of one finger with ink from a pen, and then touch the document (leaving a small black blot) where we touch a wafer. The mark [Pg 36] so made is called 'tep-sai', 'tep' meaning 'pressure' by touch or grip, and 'sai' meaning 'token' (I do not know the etymology) . I ask my readers now to compare the 'tep-sai' with the 'finger-print' alongside it, and to say whether the tep-sai could afford any means of identification by comparison with another blot from the same finger. ”

“ When the skin-pattern is impressed upon soft sealing-wax, clay, putty, and so on, the relievo image produced is different in this way from an ordinary ink-printed pattern. The convex ridges are now concave furrows, while the hollows are changed into heights.
In both kinds of impressions a reverse or mirror pattern is produced, a matter of some practical importance. This effect may, or may not again be reversed in the photographic process. It is not impossible, in such circumstances, that a suspect’s finger might be confused with a resembling “mirror” pattern, which was really not his own. ”

“ No printer who uses illustrations should be without a wood engraving outfit, consisting of four to six tools, and the cunning to use it. There are many cases in which a process plate, or a chalk plate, or old wood type, can be cleaned up, altered or improved with a little handwork. Sometimes in a zinc plate the fine lines in a sky print clearly on a small run, but soon begin to round and flatten; if not essential to the design they may then be entirely cut out {231} and the run continued. In chalk plate, surfaces may be cast black and then cut into with a white line, as in the Schafhausen. ”

“ After the finger is inked, the square is rolled around the finger without letting it slip. Extreme caution should be exercised to see that each square bears the correct fingerprint impression. After all the inked impressions are properly taken, the ten squares bearing the impressions are pasted or stapled to a standard fingerprint card in their proper positions, i.e., right thumb, right index, right middle, etc. ”

“ I fear that he has failed, like some other writers, [9] to see the definite force of the word 'identification' in the finger-print system. It means that if a man can be indicated whose finger-print agrees with that on a document, he is identified with the man who put that one there. That is all we want. But it will be seen that there must be two [Pg 41] impressions at least, that will bear comparison, to constitute 'identification'. ”