Origin of the "Powder Rubbing" Technique
                                                                                                                                                                                                                                                                                                                            Page updated 18 May 2008 
   
Extracted from "Super Glue Sticks It to the Bad Guys", published in Identification News, Vol. 34, No. 2, March 1984, pages 7-11, by Michael R. Grimm, CLPE and Richard A. Taylor, CLPE, both employed by the Virginia State Crime Laboratory in Roanoke, Virginia, USA.
  
... Within the past month a discovery was made involving the use of super glue to process plastic bags from two drug cases and a petit larceny of a black powder pistol kit. In the first case sixteen baggies were processed in the conventional manner - with only one showing a little ridge detail of no value for identification. While holding the bag up to the light for better viewing it slipped out of the examiner's hand, which was protected by the use of rubber surgeons gloves. Upon examination of the area that was under the thumb and forefinger where the bag was held, it was noted that ridge detail had “appeared,” white ridges with a very light brown colored background! Further deliberate ‘ rubbing ‘ of the bag with the rubber surgeons gloves produced two fingerprints of value for identification. Subsequent treatment of the remaining fifteen bags resulted in two more fingerprints of value, two of which were later identified as the fingerprints of one of the suspects. Similar treatment of the cellophane wrapped pistol kit produced a palm impression of extreme clarity showing even the fine pore structure of the ridges. The latest case entailed the processing of eight bags of cocaine.  Conventional methods produced no discernible ridge detail.  However, use of the "rubbing technique" supplied the examiner with two fingerprints later identified as those of one of the suspects.

The “rubbing” technique appears to change the black powdered surface to a shade of light to medium brown with the ridge detail appearing in white.  Very vigorous rubbing seems to enhance the ridge detail rather than delete it as you might expect....
  

Webservant note:  In the decades since the post-cyanoacrylate (super glue) "powder rubbing" process was published, many agencies have adopted it as the last step in examining any nonporous (glass, metal, plastic, etc.) surface.  Because cyanoacrylate polymerization creates a relatively strong three-dimensional  structure when latent prints are developed, powder can be rubbed over such cyano-processed prints (as a last step in the processing sequence).  The powder rubbing process can create contrast that enables photography and identification of previously undetected friction ridge impressions. 

The color of the friction ridge detail developed with this process depends on several factors, including the following:

  • The color of powder used;
  • The presence of contaminants on the surface;
  • Whether the friction ridge impression was deposited from the finger/palm, or was caused by the finger/palm removing (lifting away) part of a contaminate coating already present on the surface.

The basic concept is that the powder is rubbed on the relatively smooth surface bearing hard, three-dimensional (super glue-developed) ridges and furrows of cyanoacrylate polymer, causing contrast by filling furrows and accumulating powder on each side of the three dimensional friction ridge detail.

Many latent print examiners have used this technique to reveal impressions that were previously invisible by cyanyo-fuming followed with dye-stains, laser examination and "normal dusting" with fingerprint powders.  Sometimes the failure of detection through dye staining and laser (or alternate light sources) exam may be due to background/substrate luminescence  that quenches (competes with) the faint glowing of weak (minute deposit) friction ridge impressions.  Sometimes the lack of detection through normal dusting after cyano-fuming may be due to the absence of sufficiently "sticky" friction ridge deposits.  

This technique is simple, inexpensive, and risks nothing when all conventional techniques have already been exhausted without developing identifiable latent prints. 

Nothing works to successfully develop latent prints on all nonporous surfaces and the powder rubbing technique will definitely not produce successful results each time it is used.  However, consistent use as a last-step procedure on nonporous surfaces will produce enough successful instances to convince examiners to always consider it when all other steps have failed.