Hypersensitisation/hypersensitization.
Also “gas hypering” or “hydrogen hypering.” Treating films in order to reduce the effects of low-intensity reciprocity failure. The practice is quite common in astrophotography, where long time exposures are required.
Reciprocity failure in film is related to the presence of water and/or oxygen in the film emulsion. Undeveloped film can be unspooled, wound onto a wire spool and then placed in a tank (hypering tank) in a vacuum or near vacuum to drive out (outgas) the water and oxygen. Hydrogen gas - or safer “forming gas” consisting of nitrogen and around 8-10% hydrogen - is then pumped into the container to increase the base fog of the film very slightly. This is done at fairly high temperatures (eg: 50° C) for many hours and is called baking in the gas.
Note that the use of pure hydrogen is not recommended, primarily owing to its dangerously explosive tendencies. Pure hydrogen also tends to induce colour shifts in colour emulsions owing to the gas reaching different layers of film in different amounts.
cf. astrophotography, forming gas, low-intensity reciprocity failure, hypering tank, reciprocity, reciprocity failure, spiral reel.
Entry last updated 2002-05-09. Term 621 of 1487.
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