SCIENCE AND THE FORGER
By F. SHERWOOD TAYLOR
SCIENCE has added but little to the resources of the criminal. The oxy-acetylene blowpipe, dynamite and the machine-gun have somewhat enlarged his equipment, but personal skill remains the chief means of accomplishing his aims. To the detection of crime science has made great contributions, chief of which, perhaps, is the power to examine minutely and identify with certainty the source of small quantities of material by aid of the microscope, micro-chemical tests and examination by ultra-violet light.
No criminal has been worse treated by Science than has the forger. It is true that the first and most difficult step in his detection is to realise the possibility that an apparently innocent document may be a forgery. Once suspicion is roused, however, science can bring a formidable armament to bear on the problem.
The forgery of bank-notes and cheques is familiar ; but in 1934 the work of Carter and Pollard revealed the existence of a new field for the forger's activities. They showed conclusively that there existed a mass of spurious books and pamphlets, purporting to be small editions of poems, or essays, printed by nineteenth-century authors for private circulation. Some fifty editions of forged pamphlets, includ- ing works by Wordsworth, Tennyson, Rossetti, Browning, Stevenson and Ruskin, appeared to be in circulation ; and before their spurious character was proved hundreds of these had fetched high prices in the auction rooms over a period of thirty years.
The exposure of a forgery is only likely to arise through its imperfection. The contents of the document may be inconsistent with its date or character, the type or calligraphy may be imperfect copies of the original, and the materials— paper, ink, dyes, &c.—may be such as to reveal its spurious character. To compose a literary forgery requires consider- able bibliographical knowledge. Most compositions receive several revisions between the time of their first committal to type and their final reception into the author's collected works. Among the forged pamphlets exposed by Carter and Pollard was an " Author's Private Edition " of Tennyson's The Last Tournament. It happens that this poem appeared first in the Contemporary Review. Tennyson made numerous corrections to this earlier rendering before it finally appeared in Gareth and Lynette and a leaf of his corrected proof has survived. Collation of the pamphlet with this shows that the forgery reproduces minor corrections, as made by Tennyson on the above proof-sheet, though several major alterations made by him correspond to the earlier state. The only explanation of this is that the forger took his text from Gareth and Lynette, compared it carelessly with the Contemporary Review text, and restored only the major changes to their earlier form. Such methods of detection are by no means always available ; and examination of type, calligraphy and materials may be more promising.
The forger who wishes to copy a document exactly has a very difficult task. Photographic reproduction is easy and perfectly exact, but the final result, printed from a block, is very easily distinguished from the work of type. The forger exposed by Carter and Pollard was clever enough to ensure that there was no original for comparison, for he forged what purported to be a hitherto unknown edition. Even so he made mistakes. Most of his pamphlets were dated between 185o and 188o, but his type showed certain peculiarities which identified it as a fount which was not cut before 1880.
In the majority of criminal cases it is handwriting or typescript, rather than printed matter, which requires examination. Until 1854 the English Courts refused to receive the evidence furnished by comparison of genuine specimens of handwriting with the specimen whose authen- ticity was in doubt : before that date the evidence only of those who had long personal knowledge of the genuine handwriting was admitted. The intuitive recognition of handwriting is valuable, but microscopic evidence and mea surement of parts of letters and the angles between them are equally so. The minute characteristics of handwriting are usually unknown to the writer and are unlikely to be disguised by him or imitated by another. An interesting case is the traced signature. If you sign your name on two sheets of paper, superpose them and hold them to the light, you will see that the signatures never correspond exactly : a traced signature on the other hand corresponds precisely with its original. Thus a document containing two or more abso- lutely identical signatures is certain to be forged. Typescript is hardly less characteristic than handwriting. By photo- graphing the lettering on an enlarged scale through a screen ruled with fine squares to facilitate measurement it is found that every machine produces work with individual characters of alignment and spacing. The types themselves are designedly made slightly concave, consequently certain parts of letters may print more darkly than others. The number of such irdividual characters in a typewriter is so great that the probability of two typewriters giving absolutely identical work has been estimated as less than one in a billion.
Almost all forgeries are on paper, which is a variable and characteristic substance. Paper is, of course, a tangle of vegetable fibres, intermixed with a mineral " loading " which is usually an opaque white substance, such as china- clay, or barium sulphate, and with " sizing " such as starch, casein., glue, rosin, &c. The various constituents of paper were introduced at different dates and give valuable clues to its age.
Before 1861 all paper was made of rags with occasionally some admixture of straw. Before 1600 the rags were of linen only. After that date some admixture of cotton became common : the presence of artificial silk fibres is to be expected in a rag paper made later than 192o. From 1861 the fibre of esparto grass was used and after 188o " chemical wood "—wood-pulp bleached by sulphites. These fibres, when viewed under the microscope, appear quite different.
The most conclusive proof that the majority of the pamph- lets discussed by Carter and Pollard were forgeries lay in the character of the paper. The " private edition " of Tennyson's Morte d'Arthur, dated 1842, proved to be printed on a paper composed of esparto grass, introduced in 1861, and chemical wood, introduced in 1880.
Inks provide no less a problem for the forger of documents. The oldest inks owe their blackness to carbon particles, as does india ink, and were essentially a mixture of lampblack and gum-water. From perhaps the second century A.D. onward inks composed of a mixture of iron sulphate and an infusion of galls with some gum and salt came into use and were not improved on until about 1836. Such inks depended for their colour on oxidation by the air, so were somewhat pale when first applied to the paper, becoming much darker on drying. From 1836 onwards (in this country) indigo and other dyes were added to ink to give it a strong colour while still wet. Several forgeries have been detected by the presence of aniline dyes in writing supposed to have been much earlier than 1867, the date of their introduction.
The newest weapons for the detection of forgeries are the ultra-violet and infra-red rays. Substances reflect ultra-violet light in a manner quite different from that in which they reflect common light. Thus where writing has been erased colourless salts may remain absorbed in the neighbouring paper-fibres, and the erasure, though imper- ceptible in common light to eye or camera, may show up clearly in a photograph taken by ultra-violet light. These rays, moreover, excite fluorescence in most substances. Ultra-violet light, from which ordinary light has been filtered out by a dark screen of Wood's glass, is invisible ; but when it strikes most substances they absorb it and give out some of its energy in the form of ordinary light. Thus most objects when examined by ultra-violet light glow with a characteristic coloured radiance. Different papers shine out with different coloured lights. In one case a skilled forger had altered a perforated cheque by filling up some of the holes with paper-pulp and punching others, but examina- tion in the above manner caused the new filling to shine out with quite a different tint from that given by the sur- rounding paper. Imitation watermarks are sometimes forged by stamping the pattern in paraffin wax which renders the paper more transparent. This wax glows brilliantly under ultra-violet light and can at once be detected.
The infra-red rays have their uses. Thus writing ink is relatively transparent to these rays, and may be hardly visible in a photograph taken in this light : aniline inks, too, are much more transparent than ordinary inks. Ancient documents, of which a part has been obliterated by a censor, can easily be read in this way.
Most remarkable of all, perhaps, is the power to photograph a document through a closed envelope ; this depends on the fact that paper is almost transparent to infra-red light, while printers' ink is not so.
No doubt the forger will continue to flourish because in so many cases no close examination of his products is made. But the ease of ultra-violet ray examination is causing many banks and financial houses to adopt it as a routine procedure. This may lead to a decrease in forgery, or on the other hand it may lead the forger to invent methods which ultra-violet ray analysis will not detect. If I were a book collector I should certainly submit a rare pamphlet to the rays of a Wood's lamp ; I might even purchase a microscope and acquire the technique of recognising esparto grass and chemical wood.
Previous page
