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A cure may be at hand for underexposed Christmas photos. Standard films need
10 to 30 photons of incident light to generate a single dark spot on the
negative. The light produces electrons when it hits the film’s silver halide
crystals, but in standard films, many of the electrons are lost before they make
the metallic silver that creates dark spots. Jaqueline Belloni of the University
of Paris-Sud found that formate added to the film (Nature, vol 402, p
865) kept the electrons from straying, and also scavenged light energy for extra
silver atoms. This meant it took only an average of 15 photons to produce a dark
spot.