CLPEX Chat Board

Greetings,
Can anyone point me to literature that discusses the occasional situation where, specifically, CA development occurs on the substrate or it's contaminants, thus revealing a take-away impression? In other words, the fingerprint "contact" was not developed as a deposit per-se, but instead a void ( complete with ridge detail ), and if not for the CA residue development of the background, the print would not be visible. Everything I'm finding online deals with the development of the constituents of the print as a deposit.
TAS

It would be my guess that the literature does not exist due to the rarity of the conditions. Cyanoacrylate polymerizes in the presence of sodium lactate or alanine and to a lesser degree the inside of the CA tank

Take away prints in my experience happen when a dry medium adheres to the moisture on the fingers. I most often see this in dust on entertainment centers during a res burg or on the exterior of a car when it is dusty or it's spring time with pollen. In each of the take away scenarios however, the deposition of fingerprint residue is prevented due to the adherence of said dust/pollen to the residue. Plus, I don't know anyone who CA Fumes the exterior of cars or entertainment centers, except maybe Steve.

Does anyone else have any other more common experiences where the conditions might present differently?

One of my favorite exercises I provide to trainees is to give them black finger print ink and white copy paper. Using only those two items and one of their fingers, I challenge them to deposit prints onto the paper with light ridges and dark furrows. How do they accomplish the task? I will check for answers soon. JohnV

You're killing me JohnV.

I can't figure this one out. I tried licking my fingers first, I tried heavy pressure, I tried rotation - I fee like this is one of those simple things I'm overlooking but I am also not the brightest in the pack.

Touch the inked paper with your fingers, then flip the inked paper over and press it against the copy paper.

subtraction. Put a thin layer of ink on the paper and touch it with a clean finger? The ridges would look lighter by comparison. (works on a glass plate when rolling fingerprints, not sure about paper)

Put just enough black ink onto a finger. Rub the ink into the furrows and onto the summits of the ridges. The finger is covered in a coat of ink. Lightly touch white paper a number of times until ink is significantly removed from the summits of the ridges. Then, press heavily onto the paper. More furrow ink than ridge summit ink is transferred to the paper. The print appears as a reversed color print. But it is not a take-away print because it did not take anything away.

Think of the ink fingerprint cards back in the day. The stand held multiple cards because of the needs for different agencies/records. If the operator did not properly replenish the ink onto the arrestee's fingers and only pressed the fingers heavily onto subsequent cards, prints on the subsequent cards might appear as reversed color: black furrows and light ridges.

A finger is coated in residue. The finger touches many things. Residue is reduced on the summits. Residue remains in the furrows. Then the finger touches something using heavy pressure. More furrow residue is transferred than summit residue. Cyanoacrylate develops residue. The print appears as a reversed color print. But it is not a take-away print because it did not take anything away. Cyanoacrylate does not care if the residue came from the summits or furrows.

For the original concern: Did cyanoacrylate develop summit residue or furrow residue?

John Vanderkolk wrote: ↑Wed Mar 03, 2021 7:06 pm Put just enough black ink onto a finger. Rub the ink into the furrows and onto the summits of the ridges. The finger is covered in a coat of ink. Lightly touch white paper a number of times until ink is significantly removed from the summits of the ridges. Then, press heavily onto the paper. More furrow ink than ridge summit ink is transferred to the paper. The print appears as a reversed color print. But it is not a take-away print because it did not take anything away.

Pretty much the way bloody prints frequently appear as reverse color, too. Good brain teaser, John!

This is the best that I could do with a Porelon pad. A PerfectPrint pad was even worse and believe it or not, we don't have printer's ink anymore!

It's definitely more noticeable around the core but as you get away from that, the ridges are still dark - more than likely because I didn't use heavy pressure out there. The RGB values are similar between the ridges on the exterior of the pattern and the core area. But the extra ink gets squished in between the ridges and results in a darker color or more closely to that of the ink. Nonetheless, a great exercise for a trainee and one that I will steal (if I ever get to use it on a trainee!!!)

Thanks all for the commentary - I am going to add this to my list of things I want to look at further but with regard to VMD processing.