Ninhydrin Wives' Tales?

[Heidi Eldridge]

Hello again!

For those of you who used to know me, this is Heidi Fraser; I just got married and got a new account name, so "Heidi Eldridge" is what you'll see from now on.

I have some questions about ninhydrin. We're going through our Procedures Manual and doing a lot of questioning of how "things have always been done" in an attempt to substantiate WHY we do things the way we do them. We've found that a lot of our written policies seem to have their roots in oral tradition, and we're trying to track down actual research that shows these things are not simply forensic wives' tales. I was hoping some of you could help me out...

Do any of you have citations (or personal empirical knowledge of the reasons) for:

(1) Letting ninhydrin sit for 24 hours after processing to develop before evaluating prints;
(2) Letting ninhydrin sit in the dark while developing.

Or do you even do it this way? I was always told the 24 hour thing was sort of arbitrary and based on the fact that prints can continue to develop for an unknown amount of time, but due to operational needs, a line needs to be drawn somewhere to get casework out the door. Has anyone else heard differently? Anyone know of any studies?

And as far as the dark thing goes -- is it even necessary?

Thanks all!

[atorres]

Hey Heidi,

Being sort of new to the field, I can only tell you what I/we do now at my agency and what I did before coming to KCSO...

At KCSO we have a DFO/Nin oven that we use. You set the temp, humidity and time depending on what process you are using. With Nin. the temp is set at 80, the humidity is at 65% and the time is at 5 min.

Before, when I was down at Salem PD, we used a steam iron. Plug it in, use a little heat (not directly on the evidence) and then use some steam. Which, if you dont have or cannot afford one of those ovens a steam iron worked pretty well for me.

I have heard leaving it for 24 hours, which I think was what was done before steam irons and the oven. I don't have any papers in regards to the 24 hour time. I have not heard the dark, but I know when using 1,2-Indanedione you are suppose to put the evidence in the dark for 24 hours. Again, I am sure there is some research or papers about this, but I dont have any. Hope this helps. Let me know if you have any other questions. I am sure there will be a lot of people who will reply, who will have more info.

Anne

[kevin]

HFE and Heptane mixes I would let sit for 24 hours + bagged up if you don't have a heat/humidity chamber.

Those are the two that seem to have a bit of developement lag in my experience. A steam iron will sometimes not get hot enough for HFE so I would sit on those for a longer time but again, but I am basing that off of experience. It has more to do with what your working solution is but I think the carrier plays a role as well. I have seen stuff come up after being processed and photographed during a technical review in the past and dropped a note about it into the procedure manual to account for those situations ('...to remain sealed for at least 24 hours' or something to that effect). Sorry if that is not much help- I feel your pain there.

[Dogs Nose]

Hi Heidi,

Can't help with references, but the reason you leave Nin 24 hours vs using an oven or iron to heat is to avoid background discolouration (poor contrast). When you heat the document you will find the background will go a light purple colour so the contrast is not as great as it is with the (most often) white background of letting the reaction occur naturally over time. You can easily test the difference in the lab yourself.

We still stock Nin but very rarely use it. Indanedione Zinc is far superior in my humble opinion. No waiting and the photos look impressive at court with fluoro ridges (fine detail easier to see as a result). The DFO vs Ind-Zinc argument is all the rage these days apparently, your position just depends on where in the world you are.

DN

[RL Tavernaro]

Heidi,

Can't provide published references at this time, however can provide some empirical experience.

I think 'Dog's nose' has it right about background discoloration being reduced, although I believe that slower development without the application of heat/steam/humidity is the controlling factor. We actually did some research & testing in the Arizona state lab quite a number of years ago, although to my knowledge the results were not published outside our lab system. One portion I recollect was in attempting to come up with an efficient and productive method of developing latent prints on large amounts of currency. (I once had to process 14,500 'one dollar' bills... using traditional ninhydrin spray & steam iron netted 3 identifiable latent prints, one of which was ID'd to suspect).

Most examiners know there is a background problem with processing used paper currency with ninhydrin, due to the absorption into the paper of amino acids when being handled repetitively. What may not be as well known is that even brand new, uncirculated bills have also been problematic. A Secret Service agent once suggested to me that the problem came from the use of animal fat in the paper 'sizing' formula used on U.S. currency. Basically, the use of ninhydrin to process U.S. currency, along with traditional heat/humidity acceleration would result in a strong purple background, obliterating any latent prints.

We found that currency could be processed in bulk by dipping a large, loose 'roll' of currency in a large beaker of ninhydrin/heptane just long enough to completely soak all bills, and then allowing to air dry at room temperature. Latent fingerprints would tend to develop faster than the background, so a visual check would be made every few hours, photographing prints as they became visible. After 24 hours (sometimes sooner), the background would tend to overpower the latent prints. We experienced a significant increase in identifiable latent prints developed.

In general, I would also add that when practical, it is a good practice to wait 24 hours or more to check for additional latent prints becoming visible, even when heat/humidity were previously used as an accelerant. I have personally experienced pulling evidence for court and finding additional ninhydrin developed latent prints, documented by photographs taken of the same area at the time of original examination without the prints being visible.
Regards, RLT

[Neville]

And continues to develop for over a month later. I soon learned to point out in court that prints that were not visible a year ago may now be visible so I have not compared those, also that the prints I identified may not now be visible as they fade with time. Yes I was caught out with that one very embarrassing when you can't see the print; luckily the label with my writing on it was still there.