Paper AS+SS-WeM5
What Came First? The Black Ink or the Black Ink? That Is the Question

Wednesday, November 9, 2016, 9:20 am, Room 101B

Determining the order of deposition of ink markings in questioned documents (forgeries) is an important forensic task. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) has received attention as a possible technique for this purpose because it is a surface sensitive technique that can provide chemical images, potentially resolving the top ink from the bottom ink. Furthermore, static SIMS imaging is non-destructive, which is important for the preservation of unique evidence. Prior work demonstrated that ToF-SIMS can correctly determine deposition order of intersections between inks of dissimilar colors¹, and that the order of deposition between fingerprints and ink can be elucidated if the fingerprint is on top of the ink². In order to further test the abilities and robustness of the method, intersections between similar inks need to be examined. In this study, three different black ink samples were tested (Bic^TM, Papermate^TM, and Staples^TM brand pens). Preliminary work produced inconsistent results, and indicated that a more thorough analysis of the primary ions striking the sample and of the polarity of the secondary ions collected needed to be done. Therefore, chemical images of the ink intersections were collected using Ar­₁₀₀₀⁺, Bi₃⁺, and Bi₃²⁺ primary ions, with both positive and negative secondary ion spectra. Data were analyzed using Principal Component Analysis (PCA) and Multivariate Curve Resolution (MCR). Data analysis included consideration of regions of interest as well as full image analysis, with and without restrictions to the secondary ion mass range. The results point to issues regarding incorrect apparent order of deposition, potentially based on the interactions of inks of different types. This brings the forensic use of ToF-SIMS for determining the order of deposition in ink forgeries into question, and points to the need for further research on factors that can result in incorrect apparent deposition orders.

1. A. He, D. Karpuzov and S. Xu, “Ink identification by time-of-flight secondary ion mass spectrometry”, Surface and Interface Analysis, 2006, 38 (4), 854-858.

2. N.J. Bright, R.P. Webb, S. Bleay, S. Hinder, N. Ward, J.F. Watts, K.J. Kirby and M.J. Bailey. “Determination of the Deposition Order of Overlapping Latent Fingerprints and Inks Using Secondary Ion Mass Spectrometry”, Analytical Chemistry, 2012, 84, 4083-4087.