Forensic Identification Marks on Metal Surfaces

Uncovering the Secrets of Identification Marks on Metal Surfaces

Introduction:

For students of forensic science, understanding the methods used to introduce identification marks on metal surfaces is a fascinating journey into the world of crime investigation. These marks serve as critical evidence, and knowing how they are created and restored is essential for aspiring forensic experts.

Exploring Identification Methods:

Identification marks on metal surfaces are introduced through several methods:

Cast Marks:

Creation: Cast marks are produced using molds, where molten metal is poured and cooled to imprint the mold's impressions onto the metal.

Characteristics: These marks are typically raised above the metal's surface.

Restoration Challenge: Erasing these marks makes it nearly impossible to restore the original ones.

Engraved Marks:

Types: Engraved marks come in two forms.

a. Marks Engraved by Tools: These marks are created by using sharp needle-edged tools to make indented, dot-like impressions, which can be used to form letters or numbers.

b. Marks Engraved by Electrical Engravers: Electrical engravers leave continuous impressions on metallic surfaces.

Punched Marks:

Usage: Punched marks are prevalent in identifying electric, electronic, household, and manufactured articles. They are made by striking die-bearing identification marks with a hammer.

Characteristics: The metal undergoes compression, disturbing its crystalline structure under several contours, typically to a depth of one millimeter.

Challenges and Restoration:

When identification marks are intentionally erased, it poses a challenge for forensic experts. Criminals often attempt to remove these marks by filing the metal's surface. However, these erased marks can be restored.

Restoration Technique:

The technique of applying a suitable chemical reagent for restoration is similar for most metals, although the chemical formula varies. The restoration process involves the following steps:

1. Surface Preparation: The obliterated surface is cleaned thoroughly of dirt, grease, or paint with a suitable solvent and photographed.

2. Polishing: The surface is polished until smooth using a grinding or polishing machine.

3. Heating: The surface is heated and then allowed to cool.

4. Chemical Reagent Application: A chemical reagent is applied with a cotton ball attached to a stick or glass rod.

5. Examination: The identification number is read under suitable illumination. The process is repeated until the number becomes visible. A photograph is taken as soon as the number appears, as it may disappear after subsequent reagent applications.

6. Final Photograph: The best photograph is obtained after applying a transparent oil to the metal surface.

Conclusion:

Understanding how identification marks are created and restored on metal surfaces is a fundamental aspect of forensic science education. This knowledge equips students to play a vital role in uncovering evidence and solving complex criminal cases in the future.