Electrostatic Detection (or Not) of Indented Writing in Paper which was in Contact with Plastic when the Writing was Made

The Metropolitan Police Forensic Science Laboratory in London was the first such laboratory to use an electrostatic detection device (EDD) to develop indentations in documents. The apparatus used by this laboratory became known as an Electrostatic Detection Apparatus (ESDA) [1]. As the use of ESDA continued it became apparent that there were occasions when indentations that were visible in documents by oblique light were not imaged by the electrostatic technique. However, visual examination showed corresponding indentations in the plastic bags or document wallets in which the documents had been sent to the laboratory. Specific testing was undertaken which showed that neither indented writing nor embossed writing in the side of the paper that was in direct contact with the plastic when the writing causing the distortion was made was not imaged by ESDA. Further experience of the author and colleagues, spanning decades, did not contradict those observations. In 2017, discussion with an opposing expert in a civil dispute brought to the attention of the author an electrostatic image of handwritten indentations made through a plastic document wallet. This paper reports on a small study undertaken to investigate the phenomenon.