Re: Umm. I was wondering if you could tell me the variables of a PERFECT finge-

Hello Callie,

I see that you are doing a study to see what surfaces, or if all surfaces, will yield sufficient latent prints to make a match. This sounds like an interesting study.

As I explained before, different surfaces are more likely to yield latent prints than others. Smooth, hard surfaces such as metal and glass are good materials. Porous materials such as clothing, wood and bumpy surfaces such as textured plastics are not very good.

If I understand your question, you want to know what variables are examined to make a match. Fingerprint friction ridge details are generally described in a hierarchical order at three different levels, namely, Level 1 (pattern), Level 2 (minutia points), and Level 3 (pores and ridge contours). In other words, an examiner will look at the overall latent print and see if there is a general pattern match to a known, looking for loops, points, etc. Sometimes they can be eliminated at this point. If they match, then the smaller details called minutia are examined with a magnifying glass. Finally, unique markings from the sweat pores and ridges are compared. These fine details need to be present for an examiner to call a match. In the US, there's currently no number of matching points needed for a match to be made, but generally there are 7 or 8 points of identification.

So to answer your question, although you may obtain some latent prints from some rough plastic surfaces, they may be insufficiently registered to make an identification.

A good source of information can be found at: http://www.biometrika.it/eng/wp_fingintro.html

Also look at: http://www.wvstatepolice.com/crime/latent.pdf
http://www.latent-prints.com/
http://www.crimtrac.gov.au/systems___projects_fingerprint_analysis___the_basics .html

After looking at this information, you should have a better "feel" for what a good latent print with identification detail looks like. You will have to assess the latents that you obtain from various surfaces and rank them according to their ability to be compared. Perhaps your chart will have the surfaces on the X-axis starting with the best surfaces like glass, metal and go out to the least successful such as wood and textured plastic; then along the Y-axis, plot the "likliehood of obtaining a match".

Good luck with your study.

Dale L. Laux
Forensic Scientist