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Gun Bluing to Develop Latent Prints

By H.W. “Rus” Ruslander MS. CSCSA, CLPE, D-ABMDI & CBPE

Why Use Gun Bluing….As An Aid to Investigations

With increasing frequency, the crime scene investigator, processing a scene, comes across fired cartridge casings. It is of the utmost importance to process these casings for latent fingerprints in order to assist in the identification of the perpetrator.

Develop latent fingerprints on brass cartridge casings recovered from crime scenes is an added step in helping identify the perpetrator.

Recovered casings can be dipped into diluted or undiluted gun bluing to cause a chemical reaction between the bluing and the fingerprint residue on the casing.

It seems to work best on brass casings not the nickel plated or aluminum types.

The reaction is fast and must be stopped with a water bath before the print is overexposed.

Other Processes Can Be Used

  • Super Glue  Cyanoacrylate Ester Vapors
  • Fixes Latent Prints to Surface
  • Prevents Latent From Being Damaged
  • Works Well, Gives Good Results
  • Observe MSDS Precautions   
  • Wear Eye, Hand & Respiration Protection  Work in Well Ventilated Area

Before you ever Process Real Evidence

  • Practice on similar items in the lab.
  • Document your procedures and results.
  • Keep a log of what you do for future reference.
  • Take basic and advanced training courses.
  • Discuss techniques with co-workers.
  • Be comfortable with the procedure.

Take Special Note

  • Are the shell casings all the same caliber?
  • Are they the same brand?
  • Are they the same color?
  • Color is described as white metal or yellow metal.
  • What color is the primer?         
  • What is the head stamp information?

More on Processing

  • If using Gun Bluing, NEVER dip the base in the bluing.
  • Have a fresh water dip tray readily available.
  • Watch the reaction very closely.                       
  • It only takes a few seconds to occur.
  • You can always re-apply if the reaction is too weak.
  • Always photograph any results 
  • Remember depth of field, this is a curved surface.

 Mixing the Gun Bluing

  • Can be used either full strength or diluted

If diluted

  • 50:50 is best
  • Half gun bluing and half distilled water
  • Causes reaction to slow down
  • Easier to control
  • Try various dilution ratios         
  • Use the mixture you are most comfortable with

Steps to Take

  • First, you must use tweezers, terminal pliers or forceps that will not react with the bluing. Use either plastic tools or dip metal ones in the liquid plastic sold in hardware stores.
  • Grasp casing by base, not neck.
  • This protects the primer from becoming altered by the acid.
  • Dip quickly and remove. Watch closely!

Observation   

  • Watch the reaction closely; it only takes a few seconds.
  • If you wait too long, the casing will turn black.
  • Immediately dip the casing in fresh water to stop the reaction.
  • Examine the results.
  • If reaction is not acceptable, repeat process but watch it closely.

Other Applications

  • Coins
  • Keys
  • Metallic objects




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