Highly sensitive fingerprint detection process whereby small quantities of first gold and the zinc are condensed onto a sample in a vacuum chamber. Gold provides a background onto which the zinc can condense and twi metal react with the lipid residues present in a fingerprint sample. The resulting image is then photographed. This process can raise old fingerprints, even up to 20 years old. It is most effective on smooth, non-porous surfaces, such as plastic, polyethylene, and glass. By some accounts, it can develop 100 percent more prints than Small Particle Reagent (SPR).
information source: www.cbs.com