Investigations into factors affecting the cascade developer used in ESDA-a review

The Electrostatic Detection Apparatus (ESDA) is a technique most commonly used for the visualisation of indented impressions on questioned documents. This work investigates some of the variables which are known to affect the results of ESDA and some variables which have, as yet, not been addressed. The investigation of variables included: examining the effects of different levels of indentation on different qualities of paper, chronological aging of cascade developer and the effects of repeated use of cascade developer on both the quality of results and the glass beads themselves, the effects of storage of cascade developer in a humidified environment and finally the effects of variation on the image development time. Results indicate that chronological aging of cascade developer does not have a negative effect on the quality of results and a 200 g portion of cascade developer will give good quality results for up to 30 traces before the quality will begin to deteriorate. Humidification of the cascade developer appears to have no advantages over storage in a normal environment and, in fact, the toner is lost sooner with humidification. The surface of the glass beads are affected through repeated use of cascade developer and appear to become visually smoother which may lead to a loss of attraction between them and the toner particles.