Forensic Chemistry (1921)
Discoloration of Documents.
— Occasionally documents are discoloured intentionally in order to give them a fictitious appearance of age, or they are scorched and partly burned and sometimes creased and torn for a similar reason. These same devices are also resorted to for the purpose of hiding evidence of fraud.
Discoloration due to age is largely a process of oxidation brought about by natural means and it takes place in proportion to the extent to which the paper has been exposed to the air and light, and hence the outsides and edges of old documents, which are the most exposed, become the most discoloured, the discoloration progressively diminishing towards the less exposed parts. In addition to the general discoloration, however, there are frequently on old documents brown spots due to mould which are very characteristic both in appearance and distribution. It may be mentioned that these spots become translucent when wetted with water, regaining their original appearance when dry, the smaller spots as a rule becoming entirely translucent while the larger ones remain opaque at the centre. This is a very simple test and one that may be applied to almost any document without fear of injury. Sometimes isolated brown spots not caused by mould but by iron or other impurities also occur.
Other natural causes for the discoloration of documents are exposure to dust and dirt and occasionally staining by fruit juice, grease and the excreta of rats, mice and insects. In the latter case the outsides and edges of the documents generally suffer the most. Where a document has been intentionally discoloured with dust, dirt or mud, this is evident as a rule by the discoloration showing definite streaks or lines when carefully examined, the dirt generally having been rubbed on either with a cloth or with the hand.
Discoloration may also be due to heat, in which case it is an actual partial burning of the surface of the paper, which becomes very brittle if the burning is severe, and when one side becomes scorched, unless the paper is thick, the opposite side also shows signs of burning. When a number of documents are exposed to fire while together those on the outside naturally suffer most, and those on the inside may be only slightly burned or not burned at all, and any holes produced correspond in relative position in the various documents. The edges of the documents too, being loose, always burn first. These facts are frequently forgotten by forgers whose handiwork shows a definite selective action which is unnatural, certain documents or parts of documents being burned or spared in a manner that could not possibly be accidental. In one case a piece of blank paper which had been scorched in the same suspicious manner as some forged documents was found in the house of one of the accused persons.
Artificial discoloration made to simulate age is produced by means of a coloured solution. The author has never been able definitely to establish the nature of any solution employed, but in the East coffee is very probable, while in the West tea might be used. A water extract of tobacco or a dilute solution of potassium permanganate would also serve the same purpose. The use of a coloured solution is generally indicated by the characteristic shape of the edges of the discoloured areas, or the way in which the liquid has run may be plainly visible, and a thin dark line sometimes occurs where there were any very marked creases on the paper at the time it was treated. Occasionally too portions of the paper, often very small, may be found which have altogether escaped the action of the solution.