Name: ______Date: ______Period: ______

Lab Practice: Fingerprint Lifting and Latent Print Disclosing Techniques

Prints are most commonly characterized by their composition or by the material in which they are left. PLASTIC PRINTSare impressions left in soft material like wax, paint, or putty. VISIBLE or PATENT PRINTSare made by transference of blood, dirt, ink, or grease. Lastly, LATENT PRINTS, which are normally invisible and must be developed before they can be seen and photographed. Print evidence is fragile. A touch will destroy one.

Part One:DUSTING FOR PRINTS (Magnetic and Non-Magnetic Dust)

The most popular developing technique is DUSTING. Most people's fingers carry a coating of perspiration and oil. When fingers come into contact with any relatively smooth surface, the friction releases the oil from between the ridges. It is for this reason that fingerprinting is sometimes called friction ridge pattern analysis. When powder is applied to the surface, it sticks to the oil and discloses, i.e., brings out, the pattern.

Dusting works well smooth surfaces like finished wood, metal, glass, plastics, Formica, and tile. It works less well on paper, cardboard, and leather. Powders vary in color, stickiness, and photographic and magnetic qualities. The most common colors are black, white, gray, aluminum, red, and gold. The best color to use is one in sharp contrast to the surface color. For example, a white or gray powder works best on a dark surface, and a black powder works best on a lighter surface.

Procedure 1:Non-Magnetic Dusting (Check off Each Step As You Accomplish It.)

____ 1.Get your finger as greasy as possible. Behind your ear or on your face is a good place to get the oils you need.

____ 2.Leave your fingerprint on a piece of laboratory glassware. Trade the glassware with a partner remembering which finger was used.

____ 3.Before the brush is used, shake or spin it in the empty jar until the bristles spread apart and become fluffy.

____ 4.Powder is never poured directly from container. Instead, hold the container upside down and back upright again. Tap on the lid and open.

____ 5.The tip of the brush is dipped into the powder left in the lid.

____ 6.The brushing is done lightly, swinging it in short, fairly quick, uniform strokes. Try to follow the general direction of the ridges so that the powder does not deposit into the valleys.

____ 7.After brushing, unroll the lifting tape about one half inch and fold it over to form a tab for handling. It is important that you not get your fingerprints on the tape.

____ 8.Pull on the roll of tape so that the rest of the exposed tape is kept slightly taut, and cover the print area about a half an inch beyond the print in either direction. Be careful not to get air bubbles under the tape. Bubbles destroy the value of the print.

____ 9.Rub the tape over the print. After the tape is firmly in place, lift the print by pulling the tape gently and evenly away from the surface. Using a scissor, liberate it from the roll.

____ 10.Quickly apply the tape to an index card. Excess tape may then be cut away.

____ 11.Repeat steps 1-10 for two more fingers, each from a different person.

____ 12.Label the card with your name and date. Label each fingerprint with the name of the person from whom it was taken and which finger it is. Identify the pattern for each print and determine the ridge count.

____ 13.Now that you’re done with the index card and you are happy with the results, throw it in the trash. Repeat this task a second time, only this time use a real fingerprint backing card. See the example on the next page for formatting your results. They are glossy and therefore are better for displaying lifted developed prints. Submit this copy to Mr. Schuster.

Fingerprint Backing Card Format: Work carefully and conserve the space.

Procedure2: Dustingwith Magnetic Powder

____ 1.Slide the applicator handle down. Place the tip of the applicator over the power to form a plume of magnetic dust.

____ 2.Sweep the powder over the surface and watch the faint ridge detail appear. Brush in the direction of the ridges.

____ 3.Lift the prints with tape just like you did for the first dusting procedure. Follow the same format. Mount them on a backing card and submit them for grading.

Part Two:Latent Print Amplification/Development

At least four other methods, other than dusting, exist for developing latent prints. IodineFuming works well on porous surfaces such as paper and unfinished wood, especially if the prints are fresh and/or if the purpose is to find out if they’re fresh. This iodine technique also leaves no trace, so no one can tell that you have looked for prints. The procedure involves placing a few iodine crystals in a fuming pipe, heating the pipe with a lighter or match, and blowing the iodine fumes through the mouthpiece of the pipe onto the surface. Iodine fumes are purple in color, although the prints that develop will be yellowish brown. Prints developed by this method disappear rapidly, so they must be photographed quickly.

Another method is Silver Nitrate. This involves spraying silver nitrate onto a surface (such as wood or cardboard) with an aspirator, or it can be applied with a brush or swab. After the liquid is in place on the surface, it is left to dry for five to ten minutes. Then the treated area is exposed to ultraviolet light. Under the right conditions, bright light works just as well as the UV light. This method produces a clear, crisp print because the chemical picks up on the salts in the perspiration. Prints developed this way also disappear after a short time, so lifting and analysis is done via photography immediately.

A fairly recent method is Superglue Fuming. Police departments will use a big storage container or aquarium along with a hotplate, like the kinds that keep coffee cups warm. A few drops of superglue are placed on the hotplate, and the object containing prints is placed into the container. The hotplate is turned on, the container is sealed, and in about fifteen or twenty minutes, any prints that were invisible are now visible in grayish tone on the object because the cyanoacrylate from the glue bonds to the print.

Another method is Ninhydrin Spray. This is a particularly useful method for all kinds of surfaces, including books and wallpaper, and is designed to develop prints that may be very old. Ninhydrin will develop prints made over 30 years old. Ninhydrin produces a blue-violet color on the developed print. The area is either soaked or sprayed. It is important to make sure the area is well ventilated. Drying takes from ten to twenty minutes, but the process can be hastened by using a heat lamp or iron.

Procedure 1: Ninhydrin Amplification

____ 1.Acquire a strip of printer paper designated for this procedure. Write your name on one end.

____ 2.Grease up your index finger and thumb and press the strip of paper between these fingers.

____ 3.Go to the fume hood and find the Ninhydrin in the processing tray.

____ 4.Using forceps, dip the sample into the Ninhydrin solution, allowing any excess to drip back into the tray. Repeat if necessary to ensure complete saturation. Recap the Ninhydrin when not in use.

____ 5.Allow the sample to the drying for at least 15 minutes.

____ 6.If the print is not showing up, heat it with the steam iron.

____ 7.Examine the results

Procedure 2: Superglue Fuming (Cyanoacrylate)

____ 1.Acquire a test tube designated for this purpose. Clean it thoroughly with a dry paper towel.

____ 2.Use a piece of masking tape and a pencil to label your tube with your name, date, and period.

____ 3.Grease up your fingers and leave clear prints on the test tube.

____ 4.Go to the fume hood and set your tube in the metal test tube rack.

____ 5.Once everyone has deposited their test tube into the rack, Mr. Schuster will activate the SuperGlue fuming.

____ 6.Examine your results.