The vapor (fumes) of the cyanoacrylate monomer tend to polymerize more quickly on a fingerprint than on the surrounding, clean surface. The polymerization shows as a white deposit. The effectiveness of this process depends on the age of the fingerprint, the conditions to which it was subjected, and the way the fuming is done.
For optimal fuming, a relatively high humidity (around 80%) is ideal. The visibility of weak prints and prints developed on non-contrasting (light-colored) surfaces can be improved with special staining solutions.
Lifting with black gelatin lifters has been found to be very effective as a means to document developed prints. Even weak prints can be found and photographed or scanned with the GLScan, see for an example the pictures below of two fingerprints developed on a coffee bag and lifted with a black Gellifter.
Fuming with cyanoacrylate has proved to be a very effective process, especially on those surfaces that do not lend themselves to dusting with fingerprint powders (such as plastics). BVDA cyanoacrylate fluid is specially formulated for fuming fingerprints
so that instead of curing quickly (solidify in the heating dish) most
or all of the liquid will vaporize.