Film agitation

Pictorial Planet

From the author of "The Art of Black and White Developing"

Film Agitation

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Agitation Consistency

I’d like to stress that consistency in the development of film is very important. Without consistency, you can never process a film the same way twice - causing obvious problems. Agitation is one of the key variables, together with time and temperature, that we must keep very tight control of.

Let me explain.

When we process the film it must be agitated enough for the developer to act evenly on the image.  On the other hand we don’t want to stand there agitating continuously or we will lose some of our edge effects and possibly cause uneven development through the solution surging across the negatives.  A problem sometimes experienced using JOBO’s and other rotary processors. 

Unfortunately, it is perceived wisdom that the minimum agitation the film should have, to ensure even development, is two inversions of the tank every 30 seconds.  This is based on kodaks recommendations for full strength  developers with short developing times (5 minutes or so). However, with more dilute developer solutions and longer development times (both of which I explain and strongly recommend in my book) I have quite happily left a film for two or three minutes without agitation to improve acutance and reduce highlight burning.  Sometimes, with certain developers such as 510-pyro, Rodinal, and Pyrocat, I have employed stand development where I leave the film for hours with no agitation at all! This has proved not dangerous, as some would have you believe but in fact, develops some of the best negatives for printing you'll have, with beautifully rich shadow detail and soft delicate highlights. With up to 36 differently exposed negatives on a roll of film we need to use these techniques to ensure they are all developed to their best.

Over Agitation

We must be able to identify problems with our agitation technique.

a. With twist agitation (using a rod in the tank) over agitation will be seen as the edges of the film being developed differently than the centre
b. With inversion agitation, even, highly developed lines running across the negatives from top and from the bottom are caused by the developer surging through the development reel. 

Both these errors can be mitigated by lessoning the agitation in both rate (times per minute) and strength (how forcefully you are agitating).

Under Agitation

Insufficient agitation of the film (often with highly active developers at full strength) also causes streaks and uneven development. This is usually most noticeable:
a. at the lower film edge where development may be considerably less than the upper part of the film
b. or as streaks below highlight areas or the top sprocket holes. 

Negatives effected in these ways are ruined but the solution to these problems is simple.

The solution
You must agitate gently and constantly for the first 30 seconds of development, thoroughly soaking the emulsion. Do not shake the tank but instead gently invert it and back every 5 seconds, that is upside down and then right way up every 5 seconds. Take it easy with the tank, shaking the tank will introduce bubbles that will get trapped and cause more problems!

Give a little twist to the tank as you invert it each way to help move the chemicals around. Again, it's a gentle twist.

After this initial 30 seconds agitate gently, he same way, for 10 seconds on each further minute.  This is Ilford's form of agitation and is a good compromise between undesirable uneven development and desirable compensation and edge effects. When you have found the agitation you are happy with do not change it. 

You have now found consistency.

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