A study to visualize and determine the sequencing of intersecting ink lines.

Determining the sequencing of intersecting ink lines is one of the current problems for forensic document examiners. The way two inks will distribute and interact with each other and the paper at the crossing is a dynamic process that can be affected by many variables. Thus, the main purpose of this manuscript is to visualize and have a more comprehensive understanding of this process as well as study a methodology for determining the correct order of intersecting ink lines. For this, overlapping layers of different types of inks from writing instruments and printers were cross-sectioned and examined with a microscope. Results from pen/pen crossings showed that liquid-liquid and gel-gel intersections tended to form a double layer but oil-oil intersections usually formed mixtures. Additionally, oil-liquid and oil-gel intersections tended to form a double layer whenever the oil ink was on top and liquid-gel intersections tended to form a double layer for almost all crossings with exception of the ones involving a gel pen ink from one manufacturer. Results from pen/printer crossings showed the formation of a double layer only when the printer ink was on top of the pen ink. On the other permutation, the pen ink tended to penetrate through the printer ink producing the mixture of both inks. The inks drying time was found to be an important factor affecting the interaction between two inks in a crossing, particularly crossings involving gel pen inks. On the contrary, the type of paper and the writing pressure showed no significant influence on the inks distribution at the crossing. The methodology developed was reproducible with overlapping layers but there were many experimental difficulties during the validation process of intersections representing real crossings. Moreover, interpretation was dependent on the operator's eye which was a limiting factor.