Agitation is important, and to understand it is very important. Let's talk about agitation and consistency.
I’d like to underline that consistency in the development of film is so important. Without consistency, you can never process a film the same way twice - causing obvious problems and endless frustration. As described at length in The Art of Black and White Developing, there are three important variables that you must learn to control with vigour.
1. Time - Being able to develop for the same time accurately again and again.
2. Temperature - maintaining the temperature throughout development.
3. Agitation - Agitating the developer in a regular and repeatable way to control the rate and type of development.
During development we must keep tight control of these three variables to maintain consistency and quality. Consistency is always a good thing in photography. Without consistency we'll never be able to make accurate, predictable, and personalised negatives/prints.
In this article I will concentrate on agitation. Of the three variables above, agitation is the one that film developers focus on perhaps the least but is essential to success:
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 developer 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 original recommendations for full strength developers with very short developing times (5 minutes or less). However, with sensibly more dilute developer solutions and subsequently longer more relaxed development times (both of which I explain and strongly recommend
in my book) I have quite safely left a film for two or three minutes without agitation. This will improve acutance and reduce highlight burnout. 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 totally safe and creates some of the best negatives for printing you'll have! Beautifully rich shadow detail, soft delicate highlights, all within the printable range of the paper. With up to 36 differently exposed negatives on a roll of film we often need to use these techniques to ensure they are all developed to their best.It's important for our success that we are able to identify problems with our agitation technique.
- Twist agitation: With twist agitation (using a rod in the tank) over agitation is seen as the edges (top and bottom) of the film being developed differently than the centre.
- Inversion agitation: With inversion agitation, over agitation is seen as evenly spaced highly developed lines running across the negatives from top and bottom of each frame. This is caused by the developer surging through the development reel.
Both these errors can be mitigated by reducing the agitation in both rate (times per minute) and strength (how forcefully you are agitating). Be gentle!Under Agitation
Insufficient agitation of the film (often with highly active developers at full strength D-76, etc) also causes streaks and uneven development but it looks very different. This is usually most noticeable:
- At one edge of the film where development may be considerably less than the other edge of the film
- Or as streaks that run down below highlight areas or down from the sprocket holes. These look more like the smears.
Negatives effected in these ways are ruined but the solution to these problems is simple.The solution
Stick to the following agitation technique with your film.
Agitate constantly for the first 30 seconds of development, thoroughly soaking the emulsion. Do not shake the tank
but instead gently but firmly invert it and back and forth every 5 seconds. Take it easy with the tank, shaking the tank will introduce bubbles that will get trapped and cause more problems so be gentle! 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 rap the tank three times against your hand or the work surface to dislodge any air bubbles that might be sticking to the film.
Now, agitate gently, the 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. Finally…
When you have found the agitation you are happy with do not change it
You have now found a good thing - consistency.
Below is a video demonstrating inversion agitation. It shows the first minute from adding the developer, agitating for the first 30 seconds, and again on the minute.
See my other blog entries:
Keeping developers fresh