Supplies:
2 – Small glass coffee cups (from Dollar Store) $2.00
1 – Small bottle of gun bluing (from Wal-Mart or sporting goods store – approx. $2.00)
1 – Pair tweezers
Several coins – quarters work best
Small cheap magnifying glass – this glass may also be used for your trace evidence lab
Instructions:
A. Place approximately 1 ounce of gun bluing into a small coffee cup or other small glass container.
B. Add approximately 1 ounce of water to gun bluing (50:50 mix).
C. Fill second small coffee cup with clean water.
D. Rub forefinger and thumb on forehead in order to ensure that plenty of body oils are on fingers. Dry fingers will be very difficult to work with.
E. Grasp a coin between your forefinger and thumb placing a fingerprint on the coin.
F. Using tweezers, dip coin in to mixture of water and gun bluing.
G. Check every few seconds for developing latent fingerprints.
H. As fingerprints appear on coins, dip the coins into the cup with the clean water to stop development process.
I. You may wish to try this experiment several times using coins and other small metal items that will not be damaged by discoloration.
J. You may need a small magnifying glass to view the fingerprints clearly.
K. Post a synopsis of your findings and experience. Your classmates will post a comment and feedback on your posting.
M. You are to review your fellow classmates’ results and experience and post a comment to their postings. (This counts for your participation grade.)
Process Summary:
Gun bluing contains cupric salt, selenious acid and an acid. Cupric ions and selenious acid are reduced by the oxidized (etched) metals of copper, aluminum, zinc & iron. The reagent etches the coin’s metal surface not protected by sebaceous-containing latent print residue, and deposits a dark-colored Cu-Se coating to reveal friction ridge detail, then immersed into the gun bluing solution. A water bath stops the chemical reaction.
Accepted Deviations:
Should the over-development occur, excess gun blueing may be removed from the metal coins using acidified hydrogen peroxide. A clear lacquer spray can be applied to the coins to stabilize the development process, and, to enhance the contrast of the developed friction ridge detail. A number of gun bluing products sold under various trade names can be used in a diluted solution to reveal friction ridge detail on cartridge surfaces.
Post a 1000 word synopsis of your activities and results to the thread that will be provided. The synopsis should include your methodology and findings.
Example of how the report should look like and the template is attached.
