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.
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).