Superglue® Fuming
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.
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