dry time after cyanoacrylate method is complete

[Tara]

How long after the fuming process is complete can you process that same item with powders/dyestain. Do you need to wait any particular period of time. In my training and experience, there has never been a designated time or pause needed to proceed on with the appropriate subsequent processing technique. What would be the reasoning (for a piece of evidence that has been fumed successfully) to give the evidence drying time overnight? It is already dry and permanent for that matter. I overheard another examiner mention this at a recent conference, and could not jusitfy the reasoning. Any thoughts... :? :?

[Lab Rat]

I don't see why there would be a need for a lag/dry time before processing. Just to prove it, put a test print on the inside of the glue chamber door or a test substrate (like I usually do) and when you are done fuming try and wipe off the print. I have never had one smear or not be dry immediately after fuming.

[Heidi Fraser]

I usually try to leave CAed items for at least half an hour after fuming... longer, when I have the time. I haven't tested this emprically (maybe someone ought to do so), but anecdotally, I have noticed from time to time that if I take my CA standard (we do ours on a piece of acetate) out of the chamber and squirt it with RAM within a few minutes of fuming, oftentimes, the standard will disappear as if the RAM washed it away and I can't see it under RAM. When I leave it to sit for a period before applying RAM, this doesn't happen.

As I said, this hasn't been tested in any kind of controlled environment, it's just an observation. But I don't like to take chances with evidence, so I always let the contents of my fuming chamber sit for half an hour to an hour.

Heidi

[Andrew Schriever]

Heidi,

I have seen the same thing with my test prints. I dont know the reason, maybe the CA polymer accumulates and it takes some time for the bonds between the CA molecules to fully harden.

I have done some testing (nothing elaborate) of variable CA fuming times to get optimal development of prints and have noticed that it seems like the edges of the prints seem to accumulate the polymer and turn that familiar whitish color quicker than the center of the print. In instances where I have stopped the fuming before the center appears fully developed and processed that print with a dye stain, sometimes the stain will wash away the center (not fully developed portion) of the print while the outer edges remain intact. Maybe, if I left these types of prints to 'cure' for a while, the CA would harden and the stain would not wash them away. I'll have to test that.

I have set my CA chamber up so that it filters the air for 15 minutes after the fuming process is complete to evacuate the remaining CA fumes. After its done processing I will usually remove the items from the chamber and examine them for any visible impressions. By the time I am done with this, in most cases, 30 minutes has elapsed between the end of the fuming process and the time I am ready to apply dye stains.

[clpexco]

I also learned during my training (when we read all available articles on CA fuming) that it is best to let the glued print "cure" for a minimum of 20 minutes upon clearing the chamber. However, I don't have a citation for you.

[Charles Parker]

I feel it is good to let it set for a time and cure.

I have seen one documented example where RAM was applied after CA Fuming, and it floated/moved some of the friction ridge detail off of the surface.