Forensics Lab 8.5: Revealing Latent Fingerprints Using Super Glue Fuming

This article incorporates, in modified form, material from the not-yet-published Illustrated Guide to Forensics Investigations: Uncover Evidence in Your Home, Lab, or Basement.

For 80 years or more, dusting was the only widely used method for raising latent fingerprints on nonporous surfaces. Various incremental improvements were made over the decades–including the introduction of superior powder formulations, fluorescent powders, and magnetic powders–but dusting for fingerprints in 1980 was essentially unchanged from print dusting in 1900. That all changed with the introduction of Super Glue fuming, which quickly became the default method for raising latent prints on nonporous surfaces. The method is simple: the object to be treated is placed in a chamber with a source of humidity present and Super Glue fumes are introduced into the chamber. Development is usually complete within a few minutes.

Dennis Hilliard comments

For fuming we have used a 10-gallon fish tank with Lexan covers. A small beaker of hot water is placed in the tank to provide humidity. An aluminum boat holds the Super Glue, with a cup warmer to warm it. You can use wire to hang plastic bags, etc. To ease clean up, cover the inside of the tank with aluminum foil that can be discarded and replaced.

Super Glue developed prints are often dusted with black powder to allow for a lift, especially on irregular surfaces for preservation by photography. DFO can be mixed with Super Glue to give a fluorescent property to the print.

Super Glue fuming works even at room temperature, although it may take hours to a day or more for development to be complete. Super Glue fuming is usually done by using special packs that emit Super Glue fumes as soon as they’re opened or by using heat to vaporize a puddle of the glue, but an alternative method is available that depends on an interesting chemical reaction between cyanoacrylate ester and cotton (as well as wool and other fabrics). The reaction between Super Glue and cotton is extremely exothermic (heat producing), which is why it’s a very bad idea to wear cotton gloves when you work with this glue. In fact, if you saturate a cotton ball with Super Glue, the cotton ball may eventually burst into flames.

Prints developed with Super Glue may be viewed and photographed directly with an oblique light source, but they are often treated with special fluorescent dyes to improve contrast and detail. Examined under an appropriate ALS with proper filtration between the eye or camera and the specimen, dye-treated Super Glue prints stand out starkly against the background. We’ll forgo dye treatment in this lab session, because most of these dyes are expensive and difficult to obtain. What we will do is fume various nonporous objects with Super Glue and observe the results.

Required Equipment and Supplies

• goggles, gloves, and protective clothing
• magnifying glass, loupe, or stereo microscope to examine specimens (optional)
• camera (optional)
• super glue fuming chamber (see Substitutions and Modifications)
• cotton balls (at least one per specimen)
• paper towels
• aluminum foil
• sodium hydroxide solution, 0.5 M (sufficient to saturate the cotton balls)
• super glue (cyanoacrylate-based, one tube or bottle)
• nonporous specimens (see Substitutions and Modifications)

The MAKE Forensic Fingerprinting Kit includes all of the specialty items needed for this lab session. Alternatively, you can purchase these items individually from Maker Shed or other laboratory supplies vendors.

Substitutions and Modifications

• You may use any disposable lidded container that is of appropriate size for your specimens. We decided to treat only small specimens, so we used a plastic tub that had contained grocery store potato salad. The interior of the fuming chamber will be covered with cured cyanoacrylate resin when you finish this lab. If you need to remove it, use acetone, a widely-available solvent that will (eventually) remove the residue. It’s better to use a disposable fuming chamber. If you intend to fume larger objects, such as beverage cans, you’ll need a larger fuming chamber than we used. If you use a larger chamber, you may want to use some stiff wire and clips to suspend the specimens rather than simply balancing them at an angle on the bottom of the chamber as we did. Some humidity must be present for best results. We simply soaked part of a paper towel in hot tap water and placed it on the bottom of the fuming chamber to provide the necessary humidity. We folded aluminum foil into small boats to contain the cotton ball and keep it isolated from the wet paper towel and the specimen itself.
• If you don’t have a bench solution of 0.5 M sodium hydroxide, you can make one up by dissolving about 2 g of sodium hydroxide in about 100 mL of cold water. (The exact concentration is not critical.) Add sodium hydroxide to the water slowly and with stirring. This process evolves considerable heat. If you don’t have pure sodium hydroxide, you can substitute an equivalent amount of any crystal drain cleaner that lists its primary ingredient as sodium hydroxide.
• Choose a variety of small, nonporous, disposable objects as test specimens. We used microscope slides, which are cheap and fit easily into our small chamber. You can also try coins, small glass or plastic bottles, and similar nonporous objects. Also obtain at least one specimen of glossy magazine paper.

Procedure

There’s some work to be done before you begin the Super Glue fuming process. First, soak several cotton balls (at least one for each specimen you intend to fume, and it’s a good idea to have a few extras) in 0.5 M sodium hydroxide solution and place them aside on a plastic or other impervious surface to dry completely. Handle these cotton balls carefully; sodium hydroxide is extremely corrosive. Make your specimens by pressing your fingers onto the nonporous objects you selected. Again, you’ll get the best results by rubbing your finger against your nose or forehead before making the impression on the objects. (Yes, we know that criminals aren’t normally this cooperative, but we want to make things as easy as possible for beginners.)

1. If you have not already done so, put on your splash goggles, gloves, and protective clothing.
2. Set up your Super Glue fuming chamber.
3. Place a moistened paper towel or a small container of hot tap water on the bottom of the chamber.
4. Fold a piece of aluminum foil into a small boat, place the boat on the bottom of the chamber, and place one of the treated cotton balls in the boat.
5. Place the specimen in the fuming chamber, as shown in Figure 8-16, orienting it so that the surface that contains the latent prints is open to the atmosphere in the chamber.

Figure 8-16. Setting up the Super Glue fuming chamber

6. Add a few drops of the glue to the cotton ball, and immediately replace the lid on the fuming chamber. The cotton ball should begin to emit fumes within a few seconds. Allow development to continue for several minutes. You can check development progress by quickly lifting the lid and examining the specimen, although this allows fumes to escape. If necessary, you can add a few more drops of super glue to the cotton ball to increase fume output, or replace the original cotton ball with a new one and add a few drops of glue.
7. When development appears to be complete, open the container (be careful of the fumes) and remove the specimen. You can dispose of the paper towel, boat, and cotton ball with household trash.
8. Place the specimen on a clean, flat surface and examine it carefully under strong oblique light with the magnifier or loupe. You should see fingerprints revealed in considerable detail as crystalline white traces. If you have a camera, shoot an image of the developed fingerprints for your records. Record the pertinent details for the specimen in your lab notebook. If the specimen is small enough, tape it to pertinent page of your lab notebook and label it.
9. Repeat steps 3 through 8 for your other specimens.

Figure 8-17 shows a latent fingerprint revealed by super glue fuming.

Figure 8-17. Latent fingerprint revealed by Super Glue fuming

Review Questions

Q1: For which specific types of surfaces is Super Glue fuming appropriate?

Q2: Is Super Glue fuming more akin to physical development processes such as dusting, or to chemical development processes, such as ninhydrin? Why?

Q3: What other treatments are commonly used after Super Glue fuming?

August 16, 2009