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Serial Number Restoration Laboratory Exercise. Serial Number Restoration is a procedure commonly performed in forensic crime laboratories to determine the original owner of an item. Criminals commonly obliterate a serial number in an attempt to make tracing the number impossible.
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Serial Number Restoration is a procedure commonly performed in forensic crime laboratories to determine the original owner of an item. Criminals commonly obliterate a serial number in an attempt to make tracing the number impossible. When serial numbers are obliterated, criminals typically only scratch the surface enough so the numbers are no longer visible to them.
Note the partial arc in the area of obliteration. This is indicative of a number with a curved upper area such as an 8, 9, or 0. The number 6 can be excluded due to its extending along the right side. Step 1. Examine the metal to see if any partial characters are visible.
Step 2. Smooth the surface • Starting with course sandpaper, begin smoothing the surface of the area of obliteration
Step 3. Polish the surface • Using progressively finer sandpaper, polish the surface until it’s smooth
Step 4. Application of Acid • Acid is swabbed with a cotton swab or dropped onto the area of obliteration to begin the etching process • Take notes on the effect of the acid on the metal • While the acid is on the surface, the cotton swab can be used to wipe the surface to facilitate viewing the number • It may take attempts with different acids to achieve results
Step 4. Application of Acid • It is important to try the different acids on the metals to note their reaction. There is a difference between an aggressive and an effective acid. The reaction with the metal should be somewhat slow and consistent. If an acid is too aggressive, the metal will be etched too quickly and there is a risk the serial number will be “burned” out. • Because of the variety of compositions of metals and alloys, it is necessary to try different acids to see which one will work best. • The ideal acid for your metal will allow you to view the serial number while the restoration process is occurring and is effective but not too aggressive.
Step 4. Application of Acid • The laboratory exercise contains two types of metals, stainless steel and carbon steel. • Stainless steel reacts best with Fry’s Reagent and Acidic Ferric Chloride • Carbon steel reacts best with 25% Nitric Acid and Acidic Ferric Chloride
Step 4. Application of Acid • Some acids will take longer than others to react with the metal. If an acid doesn’t react within a few minutes, a new acid should be used. • Acids can be blotted up with a paper towel for removal, however caution should be used as these acids are strong and will burn your skin. • As with all laboratory exercises using acids, safety glasses and protective clothing should be worn. The use of acid should be regulated to a fume hood or other well ventilated area.
Step 5. Record Serial Number • Once the serial number is visible, record your results 1 2 3 4 5
Review Original Serial Number Obliterated 1. Look for visible number fragments 2. Sand with course sandpaper 3. Polish with fine sandpaper 5. Record restored serial number 4. Apply acid
Documenting the Restoration • As numbers appear during the restoration process, write them down. At times, the complete number may be unclear. If that is the case, write down the possible numbers could be. 5 4 ? 7 ? 3 or 8 5 3 4 ? 7 0 or 9 5 3 4 2 7 0
Documenting the Restoration • On the bottom of the worksheet the reaction should be documented. Different reagents will reactdifferently with the various metals.
