1. Serial Number Restoration

2. Serial Number – A unique number typically applied to an object by a manufacturer
Serial Number Restoration – The practice of restoring an obliterated serial number by using scientific methods

3. Types of Serial Numbering Application Methods
Serial numbers can be applied in a variety of methods. Each method has unique characteristics which enable them to be differentiated from each other.

4. Dot Matrix
Dot matrix engraved serial numbers are fairly shallow and are made by a succession of dots

5. Laser Engraving
Serial numbers engraved with a laser are shallow and have a “burned” appearance.

6. Stamped Serial Numbers
Stamped serial numbers are made by using a stamp with a positive impression of a number and applying sufficient pressure to impart a negative impression of the stamp on the object
Stamping of serial numbers on objects encountered in crime laboratories (firearms, vehicles, etc) is the most common method. Because of this, the lecture and laboratory exercise will concentrate on this type of serial number application.

7. Stamped Serial Numbers

8. Stamped Serial Numbers - Theory
The compressed area at the base of the stamping is strained below the surface of the stamp mark
The diagram on the right is meant to show a side view of the distortion the metal is encountering from the stamping process.
As the force of the stamp (depicted by the green arrow) encounters the metal, we see the resulting strain throughout the thickness of the metal. The amount of distortion is shown by the bending in the lines.
The raised areas around the sides are caused by the metal swelling from the force of the stamp. This was evident on the previous slide where the number “7” had swelling around the sides.
The bottom of the valley of the top line is the area which came in contact with the tip of the stamp. This is the lowest area of the stamping and it the what is visible.

9. Obliteration
When serial numbers are obliterated, they are generally ground down beyond the lowest point of the original stamping.
This results in the visible portion of the serial number being removed.
By removing the serial number, criminals hope that the object can not be identified as having been stolen.
The red line represents the area ground in an attempt to obliterate a serial number. As you can see, it has been ground beyond the area of the lowest point of the stamp. This would result in the serial number no longer being visible.
Law enforcement uses the serial number of firearms to determine if a firearm has been reported stolen. The absence of a serial number makes it impossible to find the original owner of the firearm.

10. Obliteration
The serial number is no longer visible due to the removal of the top layer of the metal.
The area below the obliterated layer is affected by the stamping process and is the reason serial number restoration is possible.
The red line represents the new surface of the metal with the valley of the original stamping removed.

11. Visualizing Restorations
Serial numbers appear when they are acid etched due to specular reflection.
Specular reflection – light reflecting off a smooth surface
Diffuse reflection – light reflection off rough surfaces
Specular Reflection
Diffuse reflection
Rough Surface
Smooth Surface

12. Serial Number Restoration
An obliterated serial number typically has a surface that has been scratched so that the number is no longer recognizable

13. Serial Number Restoration
The first step in the process of restoring the serial number is to polish the surface by using sand paper in progressively finer grits.
Polishing the surface will help in visualizing the serial number.
The polished surface gives us specular reflection (even, consistent reflection of light) where as the area that is attacked by the acid will yield diffuse reflection (scattered reflection of light)

14. Serial Number Restoration
Acid Etching – The acid reacts with the metal and produces hydrogen gas bubbles

15. Serial Number Restoration
The result of the acid etching is a restored serial number. The dark appearance of the numbers is the result of diffuse reflection.

16. Case Studies
An ATV was suspected of having been stolen from a local dealership.
When police attempted to read the VIN (Vehicle Identification Number) it was observed that it had been obliterated.
The number in question was located on the engine

17. Case Studies
The surface with the obliterated number was located on the top of the engine block

18. Case Studies
This is the area on top of the engine where the VIN number was stamped.
The first step in the restoration process will be to sand it smooth.

19. Case Studies
After the surface was sanded, Acid was applied to the engine block.

20. Case Studies
The Vehicle Identification Number was restored to H310E Using this information, police were able to verify the ATV was stolen and press charges against the suspect. H 3 1 E - 6 6 7 4