A preliminary study of 3D depth measurement of the grooves generated by three different pens for handwriting

In order to produce a handwritten graphic trace, contact between the tip of the writing instrument and the writing medium is required. The pressure of the pen tip on the paper is necessary to ensure that there is a transfer of ink on paper, depending upon the writing instrument, the paper, the writing surface, and the author’s habit, more or less pressure will be exerted when this contact is made. In the field of forensics, the effort exerted by the writing hand is evaluated by the intensity perceived in the color and amplitude of the graphic pattern, over the depth of the groove visible on the back of the sheet. The inking of the stroke might not be directly correlated with the degree of indentation in the paper. For example, it may happen that the inking of the stroke is not directly correlated with the level of depth of the groove in the paper, therefore could be due to defects of the graphic medium dispensing, or by the speed of the movement of the hand of the writer. The measure of the depth of a writing groove and the measure of the relative pressure variation along a graphic pattern may constitute an important fact for the forensic examination of documents. The subject of this article is therefore a first metrological approach that aims to quantitatively define for any given “writing means” (i.e., pens) and “writing medium” (inks): the differences in degree of indentation for the same individual; the differences in degree of indentation, if any, for different individuals; the absolute limits that the degree of indentation can vary continuously.