A method of treating photographic emulsions to reduce the effects of reciprocity failure; also known as hypering. The most common modern technique involves soaking the film or plates in a chemically reducing gas—ideally, pure hydrogen. For amateur use, forming gas (8% hydrogen, 92% nitrogen) is preferred. Other methods include soaking the film or plates in water or ammonia; baking the emulsion for many hours at around 60°C; and briefly pre-exposing the emulsion to light (pre-flashing) to achieve a background level on top of which light from the sky will be recorded more efficiently.
Subjects: Astronomy and Astrophysics.