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Document Dating

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  P540-542

2026-08-26

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Document Dating

In addition to analyzing and comparing inks, questioned document examiners are sometimes called upon to determine if the age of a document is consistent with what it is purported to be. An example involves a situation where some writing on a docu ment is not written at the time it is dated. These cases involve determining the age of the document. The most common way of doing this is by determining the age of the ink on the document. For example, a few years ago there was a case in Michigan where a physician was accused of entering notes about a particular medical procedure in a patient’s file after the patient died. A questioned document examiner was called upon to determine if the notes were written at the time that the date on them indicated. There are a number of ways of estimating the age of an ink sample. The most common method is to examine chemical changes to the ink as it dries. When ink dries, a number of chemical processes are going on at the same time, for example, the solvent in the ink is constantly evaporating. As this happens, some of the compo nents of the ink may form polymers (e.g., resins). In addition, the dyes in the ink will change in chemical composition over time. One way of tracking the drying of ink with time is to determine how easily it will redissolve in a suitable solvent as it dries.

Inks become less soluble as they dry. This process can be tracked by TLC. IR spectrophotometry can also track this drying process. As the solvent evaporates, some of the IR peaks will decrease in intensity. As polymers form in the ink, some new peaks will appear. As the dyes in inks age, their chemical compositions change. Mass spectrometry or some types of chromatography can track this process. For example, as the composition of a dye changes, its molecular weight will change and this will be reflected in its mass spectrum. These techniques can be used to determine if one set of writings on a document is appreciably older or younger than others or if a docu ment as a whole is as old as it is purported to be. It should be kept in mind that these processes that age documents take place over a long period of time and measuring these changes may not be entirely accurate. It may take several weeks or months before a change in the ink is reliably detectable.