A Method for Determining the Condition of an ESDA or IMEDD

Many Forensic Document Examiners (FDEs) have taken steps to prepare their laboratories for accreditation.One important requirement of this process involves the testing of equipment to ensure it is in good working order and capable of providing quality results. Two instruments used to decipher indented impressions on paper are the Electrostatic Detection Apparatus (ESDA) and the Indentation Materializer Electrostatic Document Device (IMEDD). The results produced by these instruments can vary due to a number of causes including: unfavourable ambient conditions (low relative humidity), weak corona discharge, a dirty corona wire, insufficient application of toner and weak pressure generated by the vacuum pump. A simple device is described that enables the ESDA or IMEDD operator to repeatedly produce constant impressions on paper test strips. The test strip is subjected to the same experimental conditions as the questioned document and is placed on the platen each time the instrument is used. The degree to which impressions on the test strip are recovered is a function of the ambient conditions and the instrument’s condition. If test results lie outside an acceptable range, the instrument must be repaired or the test postponed until environmental conditions are favorable.