Dating of ballpoint pen ink

In this paper we describe a case in which a cash book, dated of the year 2000, was sent to the Forensic Science Division, Document Laboratory, Zurich Canton Police in March 2003. The questioned document was a list of 29 pages containing a consecutive handwritten numbering and dated entries (payments) made of blue ballpoint pen ink. By definition, a cash book has to be written by hand and the entries have to be made daily. The questioned document was suspected to have been written within a short period (e.g., a few hours) and backdated. The document lab was asked to determine the date of the entries of the questioned list. On one hand, we were asked, if the cash book had been kept on account consecutively during the period of one year, and on the other hand, the judges were interested in knowing, if the document could have been written in 2003 and back dated to 2000. To answer these questions, the document was examined for latent elements by electrostatic detection device (ESDA). The relative dating of the entries was performed by the quantification of the ballpoint pen ink dyes and their degradation products using HPLC. Results show that it is possible to determine the relative age of entries written by ballpoint pen within a relatively short time scale, if storage and supporting material of the different samples are the same or at least similar.