Why use gentle agitation when pushing Kentmere 400 to ISO 1600?
Asked 7/26/2020
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I've seen guidance for pushing Kentmere 400 to 1600 that recommends very gentle agitation and only a few agitation intervals during development. My normal black-and-white process is more vigorous, with agitation about every 30 seconds, and it has worked fine for me so far.
What is the purpose of gentler agitation when pushing film? How does it affect development, and what are the risks if agitation is too vigorous or too minimal?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
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When you push film, i.e. develop for longer than usually recommended for that particular film–developer combination, you increase the contrast index or gamma, resulting in negatives with higher contrast than normal development would yield.
The more you agitate, the more fresh developer is going to replace exhausted developer at the emulsion–developer interface. This also tends to increase contrast.
Thus the recommendation to agitate only slightly when pushing may be intended as a means of controlling contrast. Be careful though – insufficient agitation causes problems too (uneven development). Some experimentation is probably necessary to get the best performance out of any given film–developer–routine combination.
Originally by user83032. Source · Licensed CC BY-SA 4.0
user83032
5y ago
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Generated from our catalog & community — verify before relying on it.
Gentle agitation is usually recommended when pushing because both pushing and agitation tend to increase contrast.
When you push film, you develop it longer than normal for that film/developer combination. That raises negative contrast. More vigorous agitation brings fresh developer to the film surface more often, replacing exhausted developer and increasing activity at the emulsion. That can push contrast even higher.
So the idea behind gentler agitation is to help keep contrast from becoming excessive while still developing the film enough to reach the pushed speed.
There is a tradeoff: too little agitation can cause uneven development, streaking, or other irregularities because the developer becomes locally exhausted and is not refreshed evenly. Too much agitation can produce overly contrasty negatives.
In practice, agitation is part of the overall film/developer/time routine, so changing it may require testing. If your usual method works, the main reason to reduce agitation when pushing Kentmere 400 is contrast control, not because the film absolutely requires a unique technique.
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