U.S. flag

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

Performance Evaluation and Utility Assessment of Magneto-Optical Sensor Technology for Detecting and Visualizing Obliterated Serial Numbers in Firearms

NCJ Number
Date Published
March 2014
31 pages

This project evaluated magneto optical (MO) sensor technology for the detection and visualization of obliterated serial numbers in five different metals and one composite material (All materials tested are currently used by firearm manufacturers).


The evaluation found that the MO sensor technology is a valid and reliable method for identifying obliterated serial numbers in ferromagnetic materials. The MO sensor's operating principle is the Faraday-effect, which allows for the real-time visualization and analysis of the magnetic distribution of sample materials. The technology is manufactured by Matesy GmbH and is commercially available in the United States through Absolute Magnetic Measurements & Solutions, St. Petersburg, FL. This technology requires little to no sample preparation, is easy to use, and allows for the identification of obliterated serial numbers in seconds, with time increasing to minutes at lower detection limits. When compared to the current two gold standards in serial number restoration (chemical etching and magnetic particle inspection), MO sensor technology outperformed both in results and utility with the tested samples. The MO sensor technology's limitation is its configuration. For this technology to work effectively, the sensor must be in direct contact with the sample, so it can only be used on planar surfaces. Although this restriction limits the detection and restoration of obliterated serial numbers in firearms, it may not limit the detection and deciphering of alterations in documents that use magnetic ink, or the development and visualization of fingerprints using magnetic powder. This report recommends that the application of the MO sensor technology in its current configuration be tested and evaluated in questioned document and latent print examinations. 15 tables, 7 figures, and a 7-item bibliography

Date Published: March 1, 2014