The visual appearance of inks is only one clue to their composition. Sometimes two inks can look identical to the naked eye but further tests may be able to distinguish between them. Where possible non-destructive tests are used. For example inks can be examined using infra red or ultraviolet reflectance at various wavelengths or using visible light but examining emissions from the ink in the infra red area of the spectrum (infra red luminescence). Our examiners use an instrument known as a VSC 2000HR to carry out non-destructive specialised lighting examinations. Inks may also be distinguished by other more complex chemical tests but these are likely to be destructive to some extent. LGC is fortunate in having the backing of its world renowned analytical chemistry section. This means that we can use high end techniques to examine inks such as Matrix Assisted Laser Desorption Ionisation Time of Flight Mass Spectrometry.
Differentiating inks can be important in cases where a document is suspected of having been altered. A classic example is where a zero is added to a cheque making the value ten times as much. Additionally, entries which have been obliterated may be readable using these methods, for example by rendering the obliterating ink transparent under a particular light source.
Care must be taken when inks are deemed to be indistinguishable using any testing method. The fact that two inks are indistinguishable does not prove that they both came from the same pen as a large number of pens are likely to hold indistinguishable ink either because they originate from the same manufacturer or because, by chance, they contain closely similar ink.
The 'dating' of inks is a hugely complex area and depends to a large extent on the conditions used to store the document that bears the ink. Many factors affect the apparent ageing of ink including: exposure to light, heat, humidity and thickness of ink line. For these reasons a direct dating of ink lines is seldom carried out by this Laboratory. Nevertheless, other methods for providing relative dating of documents can be carried out. An example of this is the relative sequencing between two different ink strokes (i.e. was one stroke written before or after another). Examination of the intersection between the ink strokes or the intersection between an ink stroke and an indented impression may provide evidence as to the order in which they were written.