T  H  E      D  E  T  A  I  L

Monday, June 9, 2003

Good morning via the "Detail," a weekly e-mail newsletter that greets latent print examiners around the globe every Monday morning. The purpose of the Detail is to help keep you informed of the current state of affairs in the latent print community, to provide an avenue to circulate original fingerprint-related articles, and to announce important events as they happen in our field.

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One of the biggest values of the Weekly Detail is the networking opportunities it provides.  I have learned that all except the $199 Canadian Deluxe rooms at the IAI host hotel in Ottawa are booked up.  However, I have also learned that there is another hotel 1/2 a block away that has 2-bedroom suites available for less than that! ($189/night).  They also include a kitchen, living room, and a washer and dryer.  For someone willing to share a living room / kitchen and save on expenses, this works out to $95 Canadian, or about $70 US each.  The hotel name is Les Suites, and you may reach the reservation desk at: (613) 232-2000.  If you are interested in maximizing this networking opportunity, send me an e-mail regarding gender and smoking preferences, any special requests, and a short bio of yourself for the other person to see, and I will get people in contact with each other. (kaseywertheim@aol.com)  New title: webmaster / matchmaker.  :)

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Last week, Josh Bergeron shared an excellent example of the use of Adobe Photoshop to demonstrate uniqueness.  This week, Chris Grice shares his thoughts on "reverse color" latent print impressions.

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TONALLY REVERSED LATENT PRINTS

by Chris Grice
Criminalist/Certified Latent Print Examiner
Forensic Science Laboratory
State of CT-Department of Public Safety

A standard fingerprint record usually bears black friction ridges. Therefore, as latent print examiners, we are generally used to comparing black ridges in the latent print to black ridges in the inked. If the latent was developed in such a way that the ridges are light in color, such as with gray powder processing or a fluorescing reagent, a photographic tonal reversal of the latent print is routinely undertaken. Less common is the tonal reversal that occurs in some latent prints that is unrelated to any photographic intervention. The color of the ridge detail of a latent print is dependent on several factors: the background color, the method or reagent used to visualize the print, surface conditions, and whether the ridges or the furrows are developed. This report will discuss situations in which ridge detail develops and appears is in an opposite color tone than expected. 

When examining latent and patent print impressions, there can sometimes be a difficulty in the proper interpretation as to what are the ridges and what are the furrows. In most cases, natural or foreign substances present on the friction ridge skin are deposited on the surface when the surface is touched. The ridge details are therefore reproduced as a result of the same medium that was present on the friction ridge skin, and the furrows remain the color of the surface substrate. This is sometimes called a positive print. In contrast, let’ s take the example where the finger has the effect of removing, or at least pushing aside, something present on the surface substrate, usually a surface contaminate. This results in a cleared area in which the remaining surface substance outlines the ridge detail, creating a negative impression. This phenomenon is often characterized as a “take-away” print. The two impression-deposition methods can best be understood and visualized mentally by using the example of blood prints vs. prints in blood.

A “blood print” occurs when moist blood is present on an area of friction ridge skin and a surface is touched. Another possibility exists and is generally referred to as a “print in blood”.  This is when blood is already present on the surface when touched by friction ridge skin. Usually, in order for a latent print "of value" to occur in this situation, the  layer of blood on the surface must be relatively thin and partially dry and/or agglutinated.  Obviously, the specific conditions necessary to create “prints in blood” make them less commonly observed than “blood prints”. It is important to realize however, that not all blood prints are positive (true color) prints and not all prints in blood are negative (reverse color) prints. Pressing a blood-covered finger to a surface with extreme heavy pressure will force blood off the summits of the ridges and into the furrows and leave a classic negative print. 

Other situations exist which can generate tonally reversed latent prints.  Most experienced latent print examiners have had the experience of processing an extremely dirty piece of glass with visible impressions. If the dirt layer on the window has attracted moisture from high humidity or nighttime condensation, processing with dusting powders results in powder adhering to the entire background except where the friction ridge skin has removed the dirt. The normal reaction in this situation is often to start looking for ridges in the same color as your processing powders but ultimately if you do this you often will be looking at the furrows in such a situation. A print left in a dusty surface is a similar “take-away” impression. In addition, one should be conscious of the possibility of ridge/furrow tonal reversals when processing extremely heavy items that have been picked up or carried. The pressure of the fingers on the surface due to the weight involved is such that the latent print residue is pushed into the furrows in the deposition process. This phenomenon has been personally observed on safes, heavy furniture and appliances moved at scenes of crimes.

Another situation in which a “take-away” print may occur with ridge to furrow tonal reversal involves certain types of tape. When tape is freshly peeled off a roll, especially duct tape, there is a residue of adhesive left behind on the non-adhesive side of the tape. If the roll of tape is then touched before the residue dries or hardens, the friction ridges remove the largely invisible adhesive residue. Processing causes development of the adhesive background residue, while the ridge detail remains the color of the tape surface. Although these “take-away” prints on tape only occur if the roll of tape is touched before the adhesive residue dries, the development of the take-away print can be accomplished long after the residue has dried. Prints of this nature have been developed and identified on a roll of tape, which sat untouched for two years in a Police Property Room after seizure in a sexual assault and binding incident.  Although no literature has been found regarding this type of negative impression on tape, this case and several other cases personally observed demonstrate the prominence of this phenomenon. 

There are a number of techniques to aid in the correct interpretation of ridge vs. furrow orientation. Tonal reversals can usually be anticipated if the background collects so much powder that it appears as dark as the lines within the friction skin print. In the case of a print created by or in a medium of blood, a dark field of blood appearing connected to and around the friction skin print should be an indicator of the “print in blood” scenario and the ridges will likely be the areas absent of blood. Examination for pore detail can often give vital clues as to the true ridges. The pores appear as dark spots in light-colored spaces, or conversely, white spots in dark-colored spaces. With powder-developed prints, care should be taken not to misconstrue large loose excess powder particles as pores. Unfortunately, prints in the more liquid viscosity of blood fail to replicate the smaller detail, and therefore may not readily demonstrate pore detail. 

Partial tonal reversal is also not uncommon. It should be looked for when blood on the surface is taken up and re-deposited by the ridges. Slippage or slight movement of the finger or hand is not uncommon with both “blood prints” and “prints in blood” due to the increased liquid volume present.  Further, heavy pressure on one part of the print can cause partial tonal reversals in just those areas.

Recognizing what represents the ridges and valleys in a good clear latent print will present little problem to the experienced examiner. In other cases, it may be difficult or impossible to determine if the latent print is a reverse color print until it is compared to a known inked print. If the reversal is present when two prints from the same source are examined, what appears as a dividing ridge or bifurcation in one print will appear to be an ending ridge in the other. An enclosure in one print will appear as a short ridge in the other. The core will always have one more or one less apparent rod when comparing the reversed print to the un-reversed one. The easiest way to solve the dilemma of possible color reversal is to have photographs prepared of both the positive and negative images of the print in question to determine concisely if this has occurred.  Of course in the digital world of today, inverting the images is often just a mouse-click away.

Through an understanding of when and why tonal reversal can occur, the examiner can more readily detect and account for this type of distortion.  If left unaccounted, distortion might seem to the examiner like a "difference" and the identification may not be made.  Further, a thorough understanding of any phenomenon makes it easier to explain in court.


References

Cowger, James F. (1983). Friction Ridge Skin. New York, NY: Elsevier Science Publishing Co., Inc.

Hamm, Ernest D. (1989, June). Enhancement and Development of Blood Prints . Paper presented at the 74th Annual Educational Conference-International Association for Identification, Pensacola, Fla.

Lowe, Alfred J. (1988, July). Recognition and Identification of Reverse Color Latent Prints. Journal of Forensic Identification, Vol. 5.  

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Discuss this and other fingerprint-related issues on the CLPEX message board off the homepage of the website, or at (http://www.clpex.com/phpBB/viewforum.php?f=2)

And as usual, the onin.com forum (http://onin.com/fp/wwwbd/) is also available for more formal latent print-related discussions.

For discussions with an international flair, check out Dave Charlton's forum at: http://charlton97.proboards12.com/index.cgi

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FUNNY FINGERPRINT FINDS

"The Inside Story: Fetal Development Weeks 18 Through 21 
See what's happening with your baby in the fifth month! 

Week 18 

The unique swirls and whorls that are your baby's fingerprints begin to appear at the tips of her fingers this week."

http://www.parents.com/articles/pregnancy/1033.jsp

Thanks, Cari Sandberg-Berry for this week's Funny Fingerprint Find!

My FFF folder is empty, so be on the lookout and forward any FFF's you come across this week.

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