Distortion Question

[Charles Parker]

In the article “The One-Dissimilarity Doctrine in Fingerprint Identification” by then Assistant Professor John I. Thornton (I think he has his Doctorate now) that was published in 1977 on page 3 of his article (or 91 as it came from the Journal) he talks about an aspect of distortion he calls “chattered”. The full quotation goes like this “The general nature of the latent impression does not suggest that the finger registered imprecisely due to debris on the finger, nor does an examination of this impression reveal any clear indication that the finger “chattered” over the surface upon which it was developed, thereby creating an additional ridge.”
I am familiar with the term “chattered” in vehicle accident investigation, but I am interested in a more lenghty description or explanation of the term. Better yet if someone had an example of a “chattered” distortion that they would be willing to share.

I am also interested in how other examiners may use the term “overlay” and “double tap”. Are “overlay” and “double tap” just two different words for the same type of event? Or is there separate meaning such as:

Overlay---a double impression where additional friction ridges overlap an existing friction ridge image. Overlays will not coincide with ridge flow and may exhibit some type of checkering. Overlays are not immediate double impressions of ridge detail. Overlays may or may not be the same finger impression or made by the same person.

Double Tap---a subtle double impression where additional friction ridges will coincide or be close to running in the same direction as the existing ridge flow. Double taps are made in close time proximity to the first friction ridge impression. Double Taps are usually made by the same finger.

OR any other description, definition, or usage that you may have of the terms “Overlay” or “Double Tap”.

I have a problem with the time thing and I am interested in how other examiners may use or define these terms.

If you cannot answer this posting, you can e-mail me your response.

[Cindy Rennie]

Good Morning, Charles.

I like the two definitions that you have provided for 'overlay' and 'double tap'. The results are the same (superimposed ridge detail), but I think it is important to distinguish between the two so that you can explain the phenomenon in court, especially if the double tap has resulted in an extra ridge appearing in the 'found' impression.

I also think that 'chattering' results in a 'double tap' (or even a 'triple tap'?), although I have never heard the word used in relation to fingerprints.

I lead a sheltered life......

[Wayne Reutzel]

Charles,
I too like the definitions in your post. Once again we see the need to standardize the terminology we use in this field. I was amusing how another term "superimposed" slid right in there.

[C. Coppock]

Another interesting aspect of latent prints are interference patterns. Interference patterns are caused by like patterns occupying specific spaces in relationship to one another. Interference patterns common with wave frequencies (deposited friction skin ridge impression) interact at various angles to produce specific types of patterns. It is common for latent ridges of a simultaneous impression to overlap at the moment of deposition as the friction skin may move slightly in a lateral or circular direction. The resulting impression may contain the remnants of an interference pattern that produces embedded visual interference geometries that would not otherwise be found in friction skin impressions that may have only a minimal amount of distortion. The visual features where the patterns are at a point of focus along a linear axis are often described as nodal positions. These nodal positions are locations within the distortion area where interference is at minimum and maximum levels of interaction. Anti-nodal positions are were the interference is at a maximum and nodal positions are locations where the interference is at a minimum or undisturbed state. (Glenbrook South Physics Teachers Home Page) (Research Two Source Interference Patterns for more information and visual illustrations on this topic.)

Just more info for the brain.

[Cindy Rennie]

I'm not sure that my brain can take that much information so early in the morning. I obviously need more coffee.

[Charles Parker]

Craig, my knowledge in physics is a little dust and rusty so if I fall here, please pick me up.

I am not sure that “Wave Mechanics” is the way to go on describing aspects of distortion in friction ridge detail. My reasons for that are:

1. Interference patterns are generally caused by like wavelengths (impressions) where distortion may be caused by unlike patterns.
2. Interference patterns in wavelengths occupy specific spaces where friction ridges in distortion occupy random spaces
3. Interference patterns have two vectors (nodal and anti-nodal), while I believe that distortion in some latent prints can have more than two vectors involved (ie overlapping for an unspecified length of ridge).
4. Waves are in motion, ridges are static.
5. Interference patterns in wavelengths can be repeated while I am not so sure that distortion can be repeated exactly each and every time.

You have an interesting point of view, but I just do not think that “Wave Mechanics” gives itself as an easy application to distortion in friction ridges.

However you have caused me to re-think the issue. Perhaps I am trying to be too specific. Perhaps I need to generalize and simplify. For example:

Distortion: A physical change in the natural shape of friction ridges. Distortion may be described in the following manner.
1. Matrix interference.
2. Substrate interference.
3. Pattern interference.
4. Pressure interference.
5. (might have to add a number 5, I am thinking on this one)

By simplifying we can do away with all the slang words such as: chattering, overlay, double taps, double impression, background clutter, debris filled, pressure filled, etc.

It will be easier to describe distortion now. “The latent print is distorted by pattern interference”. We will not have to know or describe all those little terms anymore. Just fast quick and easy.

It seems that simplifying and generalizations are the way to go. Look at the word “unique” how it has simplified the statement “friction ridge detail is never duplicated in its most minute (mi-noot) detail”. Or the word “permanent” for the statement “friction ridges are formed before birth and barring serious injury remain unchanged throughout a persons life”. And of course “ACE-V” has certainly simplified our concept of the methodology of comparison and evaluation.

That may be the way to go. Generalize and simplify. Thanks Craig for your input.

[Charles Parker]

I knew I had seen the word “antipodal” in reference to latent prints before. There is an article published titled “Antipodal Latent Fingerprints” in the Oct. 1976 issue of the Fingerprint and Identification Magazine (V58 #14), written by Stephen C. McKasson and Joseph G. Wichmann, both document examiners with the PIS—Chicago (add another S and I am in trouble). They go on to describe it as the powder adhering to the background and not to the ridges (color reversal). It is interesting in their footnote that says [In our research we found no word to precisely cover latent prints which develop by having powder adhere to the background rather than the ridges. We have decided to use the word “Antipodal” meaning diametrically opposites as black is to white]. Funny that they could not find any reference to a “Color Reversal”?

They go on to describe a case in which half of a latent was Antipodal and the other half was normal (they did not use the word podal). They finally took a photograph and cut it along the line of division and were able to work out the differences with the known exemplars. Thank-You for Photoshop®.

I think it is interesting that most authors do not consider “Color Reversals” an aspect of distortion. They treat them on their own. However I have seen a number of latent prints that are part regular and part reversal. This could range from just a few ridges to almost all of the latent print. I would think that something that is part one color and part another would be considered distorted. I guess it depends on what your definition of distortion is.

I ran across a different one that was authored by G. Tyler Mairs in the April 1951 issue of Fingerprint and ID Magazine (Vol. 32 #10), of which the title is “Handling Latent Friction Ridge Prints”. Mr. Mairs uses the term “Intaglio Print”. Some of you who may be stamp collectors may know what Intaglio Printing is. The design is cut into a plate (not raised) and ink is applied with the excess wiped off the top of the plate and then pressed on to a paper surface with good pressure. Mr. Mairs used the term in reference to “Blood Prints” where the blood was in the furrows and not the ridges. Again a reversal.

Antipodal and Intaglio. Two terms lost in history. I guess they just never did catch on?

Also in the 1976 issue there was a latent print (right slant loop) and an inked print (right slant loop) side by side. The discussion was about the unusual identification and distortion. The latent print appeared to have about 8 ridges between the delta and core while the inked print had about 20 ridges between the delta and core. OOOWEE a discrepancy (or is it a dissimilarity—I forget which?) A good identification through. Now was that an “Overlay” or a “Double Tap”. Why a Double Tap of course.

[C. Coppock]

You can think of the "wave" aspect regarding latent prints as a frozen visual frame of a wave event. However, the wave itself is not needed, it (pattern interference) is just well described in wave mechanics. This feature is also noted in Morie patterns, which is directly related.

Craig