striations on fp tape

[sandra wiese]

Hello all! We are having a bit of a mystery here and I'm hoping for your assistance. Attached is a scanned image of a fingerprint lift. You will notice on the tape a series of striations. We have one CSI who repeatedly has these on her lifts. We have had her replace her tape, her brushes, and have her tape removal and placement (on the card) technique reviewed and she seems to be doing both in a smooth motion.

I suspect still that on-scene she is using a herky-jerky motion to remove the tape, but she works a graveyard shift and I'm not to the point yet where I am going to disrupt my entire life to shadow her during the night shift. We just gave her a magnifier to use to review her lifts for these striations and see if she can be hyper-vigilant in helping us solve this issue. It has been going on for weeks and weeks and several prints have been ruined as a result.

The striations are not substrate specific and do not happen always, just 90% of the time. Additionally, some of the striations make a turn/curve, but largely they are straight from edge to edge of the tape with inconsistent distances between them and they do not occur the length of the lift, just in spots and those spots are inconsistent across different lifts/cases.

I'm posting this here on the off chance that it is not her technique that is causing them but something else I am missing. Thoughts?

[SConner]

What is she storing her tape in, on, or under between uses? Is that pattern the result of something heavy pressing against the roll of tape and leaving its imprint? I'm theorizing that the adhesive is soft and gummy enough that the non adhesive side wouldn't have any visible indication that the roll was squished for lack of a better word. Are the striations three dimensional? Can you feel them if you scratch your finger over the tape?

[sandra wiese]

Nope, not three dimensional. Though good thinking! Her tape is stored in a kit like a small tool box. They just lay on the top in a tray. I would think during our summers that the tape could get that hot, but she works graves and in the winter it is usually 20-30 degrees here and the kit is loaded into the van at the start of shift and stays there until end of shift.

keep thinking....

[kevin]

I've seen scrathches simlilar to this when someone used a wooden popsicle stick to press out air bubbles in the tape when they were laying their lift down, but if you can't feel it in the striations in the tape then that would probably rule that out...

[Pat]

In my experience, this defect in lifting occurs when the tape is laid across a surface but not pressed firmly everywhere on the tape prior to lifting. If the tape has not stuck solidly, it can produce this type of striation in the lift.

[Shane Turnidge]

Hi Sandra, I believe the "herky jerky" tape pulling is likely part of the problem here. I've seen this condition from time to time and I'll try to offer some thoughts as to how to correct it.
(I'm guessing the direction the tape is being pulled off the roll is from right to left.)

When pulling fingerprint tape off a roll It's important to not apply too much pressure to the roll itself with one hand while the other is pulling the tape off. This creates stress in the flexible tape which can result in sprue marks. Sometimes we see these striations when the CSI is being a little too frugal with the fingerprint tape. Perhaps get your CSI to pull a larger piece of tape from the roll in one smooth quick motion and have her cut the piece she needs with a sharp knife or pair of scissors. (Do not bite and rip) Then place an end down on the substrate well in advance of the latent print and slowly but deliberately lower the angle of the tape towards the substrate over the latent while using a roller to mate the tape to the substrate, all the while keeping tension on the fingerprint tape to avoid bubbles.
Before lifting the tape from the subtrate make sure the backing (card, acetate etc.) is in a location ready to receive the fingerprint tape. Then lift the tape in a deliberate but smooth motion and place the tape on the backing medium in the same manner as the lift was created. (with a roller)

In colder climates, such as here in the "Great White North", we tell our CSI's to keep their fingerprint lifting tape in their inside jacket pocket close to their bodies to ensure the tape and the adhesives are warm and function well. Keeping the tape warmer also helps avoid those annoying rips when the fingerprint tape gets brittle. Kits that are kept in cold garages not only affect the quality of the tape but we find the fingerprint powders lose their tooth as well. It would probably be a good idea to keep them inside and warm as well.

If this problem persists perhaps create a test environment where you and your CSI do the same things to see at what stage these striations are being created. This should help you avoid the midnight shifts. 8)

I hope this helps,
Shane Turnidge

[areitnau]

Looks like it could be something like she is smoothing out the lift with a corner of her fingernail or something like a credit card.

[RM1023]

The tape was too cold when the tech pulled it off the roll. Even here in sunny California we have the same problem on the night shift. Just tell her to warm up the tape before using it. We usually see this problem with the larger 3-4 inch widths. You still need to watch out for the herky-jerky motions though.

[Cindy Homer]

If you have found the culprit, I would be interested in knowing but here are my experiences:

I have purchased fingerprint tape in the past that came with machine marks on it that looked just like this when a print was lifted. Needless to say I couldn't use any of the rolls I purchased. It is very faint and unless the CSI is a fingerprint examiner they might not even notice the striations. Your vertical striations are very uniformly spaced so machine marks would be one avenue to investigate. One other tip in case he/she isn't doing it is to always discard the first amount of tape that's been sitting exposed on the roll and use the next area that hasn't been sitting exposed. The outside surface of the roll becomes scratched even if it isn't "visibly" damaged. Again, if the CSI isn't a fingerprint examiner they might never notice. This could be the cause of the non-uniform and angled scratches.

It's probably something very simple. It would be nice to know what you end up finding.

Good luck,

Cindy

[dadof3]

I agree with the cold tape. I have the same problem during the winter months. My suggestion is to warm up the tape before use. We usually put it up in the front window and turn on the warm air defrost. Even used a hairdryer one time to warm up my tape. Usually hear it happening as you pull the tape off the roll. It makes a series of popping sounds.

[Kathy Saviers]

I had several rolls of tape from one distributor that had those marks. I changed to a different distributor and the problem vanished. It was the same time of year, same weather conditions, so I ruled out environmental issues. Plus, these marks were showing up on all of the latent prints that were being turned in so I ruled out poor technique. I took away those rolls of tape from the deputies, giving them new rolls, and the problem disappeared.

I think it was a bad run of tape with uneven adhesive distribution on the surface.

You might changing suppliers or, at least, that batch of tape.

Kathy Saviers
(out-of-work latent print examiner)