Secondary impressions of writing and ESDA-detectable paper-paper friction

Non‐destructive DNA recovery from handwritten documents using a dry vacuum technique

“…Another essential component of paper evidence examination is the detection of indented writing, which may result in valuable investigative leads. The ESDA process causes impressed markings to become visible after charged toner particles settle onto a thin mylar film (~9 µm) which is held in place atop the document by a vacuum pump [8]. The mylar foil comes into contact with the document and also lifts off adhering cellular material, as shown in a study successfully swabbing the foil surface for DNA after completion of the ESDA process.…”

Visualizing Indented Writing on Thermal Paper by the Controlled Application of Heat

“…Secondary impressions are another form of indented writing, created by the close contact of two documents. Here, impressions from the writing on the original sheet, if significantly embossed on the back surface, will create an indent on the adjacent sheet . When the impression caused by latent pressure during writing and secondary impressions appear on the same adjacent sheet, the result can be difficult to discern .…”