CLPEX Chat Board

I have read from various sources that prints developed with Ninhydrin can fade over time, but I've never seen any kind of published timeline as to when the fading starts to the point they are no longer visible. If this happened could it be re-treated with more Ninhydrin or another chemical?

I'm not sure if what I'm about to share will be of any use, but it's the best I can do in the absence of any personal research. I received some evidence on February 18, 1999 in a homicide case. The case file has since been archived, so I can't confirm the actual date I processed the evidence. It is fair to say that I would have processed it within a couple of weeks of the receipt date.

There was a handwritten note on a piece of paper that was inside the pages of a magazine. I developed a number of latents with ninhydrin, had them photographed, and subsequently identified eight of them to the defendant. Prior to trial, the Solicitor indicated he wanted me to testify to both the location and orientation of each latent on the paper. When I reviewed the evidence prior to my testimony on October 13, 2001 the vast majority of the ridge detail was no longer visible. The photographs, of course, made it possible for me to answer his questions. However, I have no way of knowing at what point the ridge detail began to fade or when it was no longer visible. All I can say is that in this particular case, it happened within 2 years, 8 months.

I'm sorry if this is not beneficial, but it's all I can currently offer.

John

A Ninhydrin reaction is a chemical reaction between ninhydrin and amino acids present in latent print residue...the reaction shows as a purple color - your typical ninhydrin reaction - overtime once all the amino acids are consumed the reaction ceases - it is at this point that the print can begin to fade...the amount of time will be dependant upon the intensity of the reaction - if you have a light reaction it will probably fade quicker than a darker more intense reaction...I have had Ninhydrin prints that are no longer visible after a few months...and I have had Ninhydrin prints that are still visible after 18 months...

The chances of "refreshing" the print once it is faded is minimal since the amino acids would have been consumed during the first application of the Ninhydrin.

I have also had ninhydrin latents appear over time. The documents would be treated and examined, and then filed awaiting return to the investigator. In some cases, it would be a month or two before the returns were done. We woud re-examine the documents before returning them, and sometimes new latents would be found.

Cindy,
Is your section using a heat/humidity cabinet in your process or just relying upon the ambient lab & office heat and humidity? The reason I ask is, given your experience, we may then be missing latents by 'trying to be efficient' in making our returns or doing follow-up procedures.
TAS

given your experience, we may then be missing latents by 'trying to be efficient' in making our returns or doing follow-up procedures

This should read "given your experience, we may then be missing latents by 'trying to be efficient' in making our returns or doing follow-up procedures TOO QUICKLY "

TAS

Members of our Document Section tell me that they put the treated documents into a sealed cabinet (about 6' high and 4'wide) with a humidifier on the floor. They turn the humidifier on and wait until the 80% of the door is covered with steam.

They turn the humidifier off and let the documents sit for about two hours. The internal temperature of the cabinet is about 100 degrees Farenheit.

(The treatment for DFO is the same except the documents are left to sit for 12 minutes, not two hours and there is no steam added).

We typically keep the documents for about a month before returning them, and we re-examine them before we send them back. (When I was doing that job, I would wait until I had a whole stack of documents to return, and do them all at once).

We have also sucessfully re-ninned documents on which the original latent has faded, and we have ninned documents that we have had in our property bureau for months or even years and obtained good latents.

I should think that it would be impossible to guage how long it takes a nin print to fade for the same reasons that it's impossible to guage for how long a latent fingerprint has been on a surface - there are just too many variables of time and atmospheric conditions.

The bottom line is that nin latents are like a box of chocolates - you never know what you're gonna get.