T. Trimpe

Types of Prints Visible prints are made when fingers touch a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink. Plastic prints are ridge impressions left on a soft material, such as putty, wax, soap, or dust. Latent prints: Once the finger touches a surface, body perspiration and/or oils present on the finger ridges are transferred to that surface, such as a tool handle, glass, door, leaving an impression.

Detecting Prints Latent prints deposited on hard and nonabsorbent surfaces (e.g., glass, mirror, tile, and painted wood) are preferably developed by the application of a powder; Prints on porous surfaces (e.g., papers, cardboard, and cloth) generally require treatment with a chemical.

Prints may be collected by revealing them with a dusting of black powder and then lifted with a piece of clear tape. Did you know? Camel hair is the most common animal hair used to make fingerprint brushes. Now many brushes (like the one above) are made out of fiberglass. RUVIS (Reflected Ultraviolet Imaging System) can locate prints without the use of chemicals or powders on most nonabsorbent surfaces.

The cyanoacrylate ester ( Super Glue® ) fuming method develops latent prints on nonporous surfaces, such as metals, electrical tape, leather, and plastic bags. Superglue placed on cotton treated with NaOH or heated Contain for 6 hours Now, can easily be done at a crime scene using a handheld wand. Bottom Right: Magnetic powder can also be used to reveal latent prints. This type of powder works better on shiny surfaces or plastic baggies or containers. ** only used on nonferrous materials** Top Left:

Chemical Detection Iodine fuming is the oldest chemical method. The fumes from heated crystals are not permanent, but can be fixed using a starch solution. Ninhydrin reacts chemically with trace amounts of amino acids present in latent prints to produce a purple- blue color. Physical Developer is a silver nitrate based liquid reagent used to visualize prints undetected by the previous 2 methods. Also works on porous materials that were wet.

Detecting Prints Once the latent print has been visualized, it must be permanently preserved for future comparison and for possible use as court evidence. A photograph must be taken before any further attempts at preservation are made.

Transporting Prints If the object is small enough to be transported without destroying the print, it should be preserved in its entirety. Prints on large immovable objects that have been developed with a powder can best be preserved by “lifting” with a broad adhesive tape. Then, the tape is placed on a properly labeled card that provides a good background contrast with the powder.

Directions: 1 - Cover your table with white butcher paper. You must dust everything on the white paper – not on your table or near the edge of the paper! 2 - Get a lifting kit from your teacher that contains black powder, brushes, and clear tape. 3 - Press the pad of your right thumb on a glass slide to make a print. 4 – Dip a brush lightly into the container of black powder and then tap off the extra on the lid. You only need a very small amount of powder to dust the print. 5 – Hold the brush over the print and rotate it between your thumb and fingers. 6 - Use a small piece of clear tape to lift the print and place it in the box on your worksheet. CAUTION: The black powder will be messy and isn’t the easy to clean up. Keep it on the white paper and don’t dust anything without permission!

Clean Up 1 – Put your brushes away in the tubes and place in the box with the tape and index cards. 2 – Slowly lift the white paper and fold it in the middle. Have someone help you tap the paper and return the extra black powder to the container. 3 – Put the black powder in the box and have it checked in by your teacher. 4 – Get a towel and “dry” wash the table – especially the edges that weren’t covered with white powder. 5 – Get a wet towel to wash off the table and then wipe it with some dry towels. 6 – Clean off the glass slides and return them to your teacher.