Several hypersensitization or "hypering" techniques have been developed to overcome this failure of the reciprocity law, and what follows refers mainly to work in astronomy.
With low-intensity light, the sub-latent image speck may rapidly revert to silver halide before sufficient photons have been absorbed to make it stable.
Washing plates in water, dilute ammonia, triethanolamine or (more recently) silver nitrate solutions[6] was found to be very effective, especially for red- and infrared-sensitive materials.
However, much skill and persistence was required to obtain consistent and uniform results, especially with large plates, which were often treated at unsocial hours in observatory darkrooms on remote mountain tops.
The liquid-phase plate washing techniques operate by removing residual soluble bromides or iodides from the emulsion, thereby increasing the silver ion concentration in the vicinity of the photosensitive grain.
From about 1970,[9] baking (about 65 °C for several hours) or prolonged soaking (20 °C for weeks) in an intermittent flow of nitrogen was used and could achieve a factor of 10 gain in speed for a one-hour exposure.
[10] This process became especially important for the new generation of high detective quantum efficiency, fine-grained (but slow) plates Eastman Kodak had developed in the late 1960s.
The gas-phase methods, especially nitrogen baking, involve the removal of traces of oxygen and water from the gelatin matrix, which increases the efficiency of the first stages of latent-image formation.
Photographic gelatin soaks up ambient moisture rapidly, so in humid climates, "hypered" plates were usually exposed at the telescope in an atmosphere of nitrogen.
Note that digital cameras of all sorts, including the DSLRs now widely used by amateur astronomers, have zero reciprocity failure and outperform even the best hypersensitized film.
[15] Cooling the emulsion during the exposure reduces reciprocity failure by extending the lifetime of the unstable single-atom stage of latent image formation.