Ink Differentiation

Document Alteration and Ink Analysis

Being asked to distinguish between two or more inks that may have been used to alter a document is a common problem posed to the Forensic Document Examiner. Additions and/or obliterations in most cases are made with ink of the same color as the original entries. Once the authenticity of a document has been questioned where an important entry has been obliterated, damaged or faded, a possible unauthorized alteration has been made or simply verifying only one ink was used to complete the document, the examiner is challenged with determining, preferable using nondestructive techniques, the true history of the document.

Modern inks are a combination of synthetic or natural dyes or pigments held in suspension, along with a volatile solvent. The resultant color may be the result of a single coloring agent or a mixture of several dyes and/or pigments. And, depending on the different coloring agents used, the reaction to light stimulus (visible and non-visible) will vary.

When ink is exposed to a specific range of light energy (infrared or visible), three (3) different reactions can occur:

  1. 1. The light, all or partial, will be reflected by the ink. This will cause the ink to appear paler or to disappear.
  2. 2. The ink will absorb the light and convert it to heat or undergo structural or chemical changes. The result is the ink will appear darker.
  3. 3. The light will be absorbed by the ink and then be re-emitted at a different wavelength, a process known as “infrared Luminescence”. The ink will brighten or appear to “glow” when visualized in the infrared region.

Drexler Document Laboratory, LLC utilized state-of-the-art instrumentation to compare and examine inks. The tests are non-destructive and results of illumination reactions are documented. It is noted that this examination can only be performed on the “original” document. In addition, examinations of this type, because of the non-portability of the equipment required, must be conducted in the laboratory.