U.S. flag

An official website of the United States government, Department of Justice.

Research and Development of Impression Evidence

NCJ Number
Date Published
February 2013
40 pages
Project goals were to develop an optimal formula composition of Magneto-Rheological (MR) casting fluid; determine the limitations and benefits of using MR solutions as a casting fluid; and if successful in these efforts, develop a method of creating 3D images for permanent storage of the casting impressions.
The MR solution developed created long-lasting, durable, and high-resolution cases, which facilitated the visualization and analysis of small details not discernible on the object that made the impression. With every MR solution, the casting substrate had to be non-porous, so that the solution was not absorbed by the substrate, as well as non-magnetic so the solution was not affected by the magnetic field of the substrate. In addition to the higher cast resolution, the cast formed instantly once the magnetic field was applied, which is not possible with modern methods. With MR fluids, impression details quickly dissipate after the magnetic field has been removed. In order for MR fluids to be used in a professional setting, a commercially available magnetized container would be necessary. The main benefit of Mikrosil and Dental Stone over the current MR fluids is the permanency of the casts and their ruggedness; however, MR fluids have the capability to collect and preserve evidence with higher accuracy at lower costs, faster set time, and with fewer user errors than Mikrosil or Dental Stone casting. The trial MR fluid compositions were developed through trial and error by adjusting the concentration of the components in the fluid. Of the trial solution prepared for this project, the optimal MR fluid consisted of 25.0 g 325 mesh iron, 0.75 g cellulose, 0.75 g sodium nitrite, 0.15 g sodium chloride, 0.5 g silicon dioxide, and 10.0 mL-distilled water. 1 table, 8 figures, 16 references, and a listing of 2 publications that have disseminated the research findings

Date Published: February 1, 2013