Assessing the Repeatability and Reproducibility of Magnetic Flux Measurements and their Potential to Discriminate Toner Printed Documents

Toner printed documents are commonly submitted for forensic examination, yet some of the methods currently applied to these samples are generally costly, time-consuming, and often provide inconclusive results. The need has been acknowledged for an analytical method which can be applied to toner printed documents which is quick, inexpensive, provides information that is complementary to other techniques, and aides in discriminating toners. The purpose of this study is to evaluate magnetic flux measurements with the following goals: (1) to assess whether magnetic flux measurements can be correlated to toner area; (2) to determine if magnetic flux values remain stable over time; and (3) to normalize magnetic flux measurements of samples with variable text and print features. The magnetic properties of documents produced by 5 electrophotography devices were measured and compared to results obtained one year prior. The area for each measurement was determined using image processing software, and the flux was plotted as a function of toner area to assess the potential relationship. A representative population of 150 toner samples was then assessed using the magnetic flux as a function of toner area as a normalizing unit to determine if significant variation could be observed. The results indicate that magnetic flux does remain stable over time and that there is a relationship between toner area and magnetic flux. The relationship between toner area and magnetic flux allowed for the normalization of data and assisted in comparison of samples with variable text and print features, which is necessary for casework application. The variation present in the population distribution was great enough to allow for discrimination based on magnetic flux measurement. Magnetic flux measurement is promising as an efficient, non-destructive method to aid in the discrimination of toner printed documents.