Superglue fuming (Forensic Science)
Forensic scientists have used superglue fuming since 1982 to visualize latent fingerprints and palm prints on nonporous surfaces such as metals and plastics. The developed prints are white and provide especially good contrast with dark-colored surfaces. Dyes such as rhodamine can be used to enhance the contrast of prints with light backgrounds and can cause prints to fluoresce when viewed under the appropriate conditions.
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How Fuming Works (Forensic Science)
Superglue, like many adhesives, is a polymer. A polymer is a type of molecule that exists in the form of long chains of repeating units, called monomers. Superglue consists almost entirely of cyanoacrylate ester, which consists of carbon, hydrogen, oxygen, and nitrogen and polymerizes (forms long chains) rapidly in the presence of minute amounts of water.
When superglue vapor comes in contact with a fingerprint on a nonporous surface, it quickly begins polymerizing. Layers of polymer build up until the minute details of the fingerprint are visible. Because the vapor interacts only with the fingerprint, the area around the details remains free of superglue. In addition to enabling visualization of the fingerprint, the superglue makes the print permanent, thus preserving it.
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Procedure (Forensic Science)
Superglue fuming is often performed in a fuming tank. The item to be fumed is suspended or propped inside a glass tank, such as an aquarium, so that the area of the item suspected to contain a fingerprint or palm print is not touching any surface of the tank. A source of superglue vapor is also required. The superglue may be vaporized in one of two ways: Either a small amount of sodium hydroxide, a very strong base, is added to the unpolymerized glue or the glue is heated. Crime labs typically employ the heating method, as it tends to be more efficient, but methods of heating the glue vary from lab to lab. The heat source can be anything from a lightbulb to a small warming plate (of the kind designed to hold a coffee mug) to a cup of boiling water.
To begin the fuming, a small amount of superglue (roughly the size of a quarter) is typically placed on an aluminum foil tray, which is then placed above the heat source inside the fuming tank, along with the item to be fumed. The tank is then sealed, and the vapor is allowed to fill the chamber. The vapor interacts with the object in the tank and develops any prints that might be present on the surface. The fuming is allowed to progress for anywhere from less than an hour to six hours, depending on the efficiency of the heat source, the lab’s protocols, the size of the tank, and the object being fumed. When the fuming is complete, the heat source is turned off and the tank is opened....
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Safety Considerations (Forensic Science)
Although superglue is nontoxic—it is even sometimes used to seal surgical wounds—the vapors given off during the fuming process will bind to skin, eyes, and mucous membranes if these are left unprotected. Persons wearing contact lenses should not come into close proximity to superglue fuming because of the possibility that the lenses will bond to the eyes. The fumes themselves can also be very irritating. To prevent exposure, laboratories generally conduct superglue fuming in chemical fume hoods, and those performing the procedure wear safety goggles and gloves and make sure that none of their skin is exposed.
If a fume hood is not available, such as when a fuming wand is used at a crime scene, extra care must be taken to ensure that no one is exposed to the fumes. In addition to wearing the kinds of personal protective gear noted above, the person using a fuming wand often employs a face mask to avoid inhaling the vapors.
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Further Reading (Forensic Science)
Champod, Christophe. Fingerprints and Other Ridge Skin Impressions. Boca Raton, Fla.: CRC Press, 2004. Comprehensive discussion of fingerprint evidence includes detailed information on superglue fuming.
Gardner, Ross M. Practical Crime Scene Processing and Investigation. Boca Raton, Fla.: CRC Press, 2005. Guide to investigating crime scenes focuses on practical applications of forensic techniques. Discusses the different kinds of tank setups used in superglue fuming.
Genge, N. E. The Forensic Casebook: The Science of Crime Scene Investigation. New York: Ballantine, 2002. Easy-to-read overview of crime scene investigation features a section on fingerprints that discusses methods of print visualization, including superglue fuming.
Jackson, Andrew R. W., and Julie M. Jackson. Forensic Science. 2d ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2008. Provides a broad overview of forensic science and includes basic information on superglue fuming of fingerprints.
Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 9th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2007. Excellent introductory textbook covers most forensic disciplines. Includes in-depth information on fingerprints.
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Superglue® Fuming (World of Forensic Science)
Superglue® fuming, also known as cyanoacrylate fuming, is one of the processes used to chemically enhance fingerprints on smooth or nonporous surfaces. When an object is subjected to superglue fuming, fingerprints that are present on its nonporous parts will appear in white. Further dying is possible, increasing the contrast with the background. This technique is one of the most used fingerprint enhancement techniques and has a paramount role in forensic sciences. It allows the observation of fingerprints that would not otherwise be detected. It was first used in 1978 by the Criminal Identification Division of the Japanese National Police Agency.
Superglues are monomeric liquids of cyanoacrylate esters. They are also known as high-strength or rapid glues. When vaporized, the cyanoacrylate ester vapors will selectively polymerize on the secretions left by fingerprints on nonporous surfaces. The resulting hard, white polycyanoacrylate coating covers the fingerprint pattern. This provides the forensic scientist with a first enhancement of the contrast of the fingerprint to the surface. If this enhancement is not enough, it is then possible, after allowing the fingerprint to dry for a moment, to apply different dyes selectively on the polymerized glue. Some of these dyes are also fluorescent (light-emitting) at given wavelengths, which greatly improves the contrast to the background.
In order to process an object for fingerprints with Superglue® fuming, the object is placed in a small chamber. The humidity inside the chamber is important, and a relative humidity of 80% is recommended; air that is too dry provides poor results. The Superglue® is placed on a hot plate and heated to about 212°F (100°C). The surfaces of the object are monitored, and the process is stopped as soon as the fingerprints appear with enough contrast. Many crime laboratories use a homemade unit, comprised of a recycled fish tank, a beaker with water, a small fan to produce humidity, and a modified soldering iron to vaporize the Superglue®. Over time, some companies have developed units specially designed for this process that allow for more accurate control of the humidity, temperature of vaporization, and vapor circulation. Different portable systems have also been developed for field work, and some police agencies have built big chambers to accommodate vehicles.
SEE ALSO Alternate light source analysis; Fingerprint; Fluorescence.