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Firearms Examiner Training

Microscopic Procedures

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Microscopic Procedures

The following should be addressed prior to any microscopic comparisons:

  • Review laboratory protocols, as needed.
  • Complete administrative requirements:
    • Chain of custody
    • Marking of evidence
    • Laboratory case identifiers
    • Investigative file identifier
    • Examiner identity
    • Quality assurance
  • Follow laboratory safety protocols.
  • Determine the presence of trace evidence and follow laboratory protocol for collection.

    Examples of trace evidence include
    • paint,
    • glass,
    • blood,
    • bone,
    • soft tissue,
    • hair,
    • fibers,
    • wood,
    • metal smears,
    • masonry,
    • stone.
  • Determine if latent fingerprint examinations should be performed prior to toolmark examinations.
  • Determine if other examinations (not requested) should be performed. If so, coordinate with the investigator.
  • After the requirements dictated by trace evidence and latent fingerprints have been addressed, the toolmarked area can be cleaned:
    • Paint may be removed by soaking the tool in alcohol or acetone.
    • Plaster may be removed by soaking the tool in 15 percent acetic acid.
    • Loose material may be removed by rinsing the tool in water or methanol.
    • Blood and other biohazards may be removed by soaking for at least one minute in a 10 percent bleach solution.

Click here to read a sample forensic worksheet and report - Toolmark Identification (Tools & Toolmarks)

Microscopic Comparisons

When conducting microscopic comparisons, considerations include these:

  • Ensure that stereo- and comparison microscopes meet all maintenance and calibration standards.
  • For the comparison microscope, select an appropriate level of magnification for both objective lenses. This setting will frequently be 1x or 2x. Ensure that the objective lenses are locked in place.
  • Select the appropriate level of magnification for both ocular lenses. This will typically be 10x. If used with the objective lenses set at 1x or 2x, this will produce a total magnification of 10x or 20x, respectively. Many examiners prefer the lower end of this range.
  • Select the same type and orientation of light source for each comparison microscope stage.

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