The chronological order of creation of crossing lines scratched into a copper surface was determined using 3D profiles
measured with SWLI and CM. As the methods used are based only on the deformations of the surface and since the
imaging techniques can be used for different materials, the proposed methods are potentially effective also on other
materials.
Determining the chronological order of orthogonally crossing lines is studied in forensic science. The order of creation of
such lines allows in some cases determination of the history of an object without comparing it to other objects.. Methods
based on two dimensional (2D) imaging have been used for this task, but such methods are ineffective if the lines are
made with a similar tool. We apply Scanning White Light Interferometry (SWLI) and Confocal Microscopy (CM) to
study crossing lines on a copper surface scratched with a scratching device. Both SWLI and CM quantitatively measure
the 3D surface profiles with sufficient accuracy for forensic applications. 3D image processing allows removing
unimportant features, such as surface form and roughness, as well as measurement noise from the measured profiles.
Separating inherent features in the crossing area, from other surface characteristics allows one to determine the sequence
of creation of the lines even on a rough and wavy surface.
Cutting tools leave characteristic marks that can connect a set of toolmarks to an individual tool. When the depth
resolution of an optical microscope is insufficient, more advanced three-dimensional (3D) imaging methods such as
Scanning White Light Interferometry (SWLI) and confocal microscopy are required. We cut ten copper wires (2.1±0.1
mm diameter) maintaining a predefined blade orientation and position using diagonal cutting pliers. Images of the
sample surfaces were created using equipment based on optical microscopy, SWLI and confocal microscopy. SWLI and
confocal microscopy set-ups can produce consistent high-resolution 3D images that are relevant for forensic toolmark
comparison.
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