Critical review and trends in forensic investigations of crossing ink lines

This manuscript presents a critical discussion of the methods and techniques proposed for determining the sequence of crossing ink lines and their advantages, limitations and effectiveness are compared. Some trends are described, such as examination of physical features using optical and electron microscopy in the 60's and 70's, the use of the lifting technique in the 80's and the ESDA in the 90's. The year 2000 introduced chemical analysis with IR and Raman spectroscopy and also surface analysis with 3D laser Profilometry, for more objective examinations. The last decade has seen the application of the VSC and hyperspectral imaging, combined with chemometrics for automated, more informative and representative examinations. Nevertheless, interpretations remain visual and blind testing can be used for method validation. Some studies addressed some of the factors affecting the crossing of two ink lines but much of the physicochemical aspects remain uncomprehended and understudied.