PUBLIC Forums => Public Forums => Technical Assistance => Topic started by: Alex Belt on June 09, 2009, 09:45:23 AM
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Our latent print section is going to begin using dye stain on some firearms. Currently, I am working with our latent section at looking at the possible effects of the process on our exams. I was wondering if anyone has noted any effects from the use of the process on firearms, including changes in individual characteristics on bullets and/or cartridge cases or the functioning of a firearm. Also, has anyone done any validation studies on the process when used on firearms? Thanks for your help!
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Several stains and rinses may be either water-based or alcohol based. I have seen issues with water-based stains causing rusting, so we like our LP section to use alcohol-based stains whenever possible. If water-based stains are used it is important that the firearms are allowed to dry to prevent surface rust. We're a state lab, so if one of our customers uses water-based stains and does not let the firearm dry prior to packaging it could be some time before anyone here gets to it. Plastic obviously makes the situation worse. I have seen heavy deposits of super glue, but this cleans up easily.
These are just my observations. We have not done any validations...
Nat
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Hi Alex.
I actually conducted a study a couple of years back that will eventually be published with IAI. Anyway, the quick version is that I worked with a crime scene investigator on this very subject. We took a series of firearms and processed them using MBD (alcohol based dye) then tried to determine whether it had an effect on the identification up to a year later. I was able to still identify the original test fires to the tests 1 year later. We found no rust on the firearms. I don't know what effect the water based dye would have long term but I suspect rust would form as Nat mentioned.
Omar
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Almost every firearm that comes through our lab gets processed for prints prior to firearms analysis, they use dye stains, and we have never once had any issues.
I double checked with them this morning, and they use both methanol based and water based dye stains. As a general rule, they will use water based on any firearms that have wood on them (rifles/ shotguns with wood stocks and forends, and pistols/revolvers with wood grips) and the methanol based on everything else.
There have probably been thousands of guns processed this way and I've never thought there was an issue. Not to say that we haven't had guns with rust, but it's never been rust that I thought might be attributed to any chemicals LP uses. And depending on the agency and the year the firearm was submitted, they may be packaged in plastic bags or cardboard boxes. With that said, they are dried before they are returned to evidence intake.
So if anyone is seeing rust they think might be because of a water based dye stain, it might likely be because it's not being dried all the way. And while I've never done latents--so this statement is purely an observation--I'm thinking that "gunk" build-up might be because they are going overboard with the dye stain. It's a rare occassion when I can even tell it's been used (i.e. end of sawed-off stocks where there is exposed, untreated wood or occasionally in a crevice).