Analysis of writing inks on questioned documents is difficult due to the limited amount of ink available for analysis. Nondestructive methods of analysis are performed prior to chemical analysis. Typical nondestructive methods include microscopic examination using white light as well as other wavelengths of light ranging from ultraviolet to infrared. These tests can reveal significant similarities or differences between questioned ink samples. Identification or characterization of inks requires extensive chemical analysis. The most common chemical methods utilized is thin layer chromatography (TLC). This technique separates the components of the ink whereby comparisons can be made between to questioned samples. Other methods such as High Performance Liquid Chromatography (HPLC) and Gas Chromatography (GC) are more sensitive and can detect the non visible components. Another aspect of ink analysis is dating of the ink. There are several methods employed to estimate when a questioned document was written. The extraction rates or percentage of ink extracted by fluorescent, absorption or density measurements are compared between a questioned sample and a known sample.
Reference: Forensic Science Handbook, Volume I, 2nd Edition, edited by Saferstein, R. (Englewood Cliffs, NJ: Prentice Hall, 2002).
NCFS Research:
- A study was conducted on the use of electrospray – mass spectrometry (ESI-MS) to discriminate black pen inks. Through a set of three methods, the type (i.e. ball point, gel, and roller) of pen was determined.
For more information contact Dr. Michael Sigman.