High Energy Milling of Micro Magnetic Powder for Fingerprint Development

Abstract

Highly reflective magnetic powders have been available commercially for latent fingerprint development on dark background surfaces for a few years, however there are needs of a superior darker variety of the magnetic powder which would be ideally suitable for obtaining good contrast on light background surfaces. A novel dark magnetic powder is therefore suggested for the application in latent fingerprint development on light backgrounds. Based on a comprehensive analysis of the manufacturing techniques for the production of metallic powders and previous experiences, a series of dry milling trials were proposed using a high energy vibratory mill. In these milling trials, atomized iron powders of appropriate particle dimensions were chosen as the starting material. The starting atomized iron powders are mixed with a specific process controlling agent in cylindrical plastic pots, which are fixed on the vibratory mill. Stainless steel balls were used as the milling medium. The amount of starting iron powders and the milling time are designated so as to obtain flakes of different particle dimensions. After the designated milling process, the powders were carefully exposed to the air to avoid catching fire and separated from the steel balls. Thereafter, the samples of the powders were inspected using scan electron microscope and the result reveals that some good quality flakes with leafy characteristics and high aspect ratio were developed. The samples of the powders were also used to develop latent fingerprints on a common background at the university’s forensic investigation laboratory, and the result indicates that some flakes obtained can be considered as good quality darker variety of magnetic powder for fingerprint development.