Sunday, 11 December 2011

Agitating the developing tank.

The main reason for inverting the developing tank is to make sure that the film gets equal treatment in the developer. One of the best ways of achieving this is to tumble the tank by turning it from end to end.

Why do we agitate the tank? The developer interacts with the emulsion of the film. It vigorously attacks the silver it come into contact with and becomes exhausted. By inverting the tank you refresh this action, producing evenly developed negatives. It is
important to get this right. To little agitation will allow by-products of the process to build up, leaving pale-toned streamers as they slide to the bottom of the tank. Likewise excessive inversions will produce currents in the developer, creating uneven development. Most process times allow for agitation.
Once the developer is added you should agitate the tank for the first thirty seconds but before you put the tank down give it a slight twist and tap it on a hard surface ( it is a good idea to lay a soft towel down so you do not damage the tank) so you dislodge any air bells/bubbles that may have attached themselves to the film. Then you need to agitate for ten seconds in every minute of the process time about four inversion per ten seconds or as the developer manufacturers instruction advise. For example PMK Pyro recommend one inversion every fifteen seconds. 
I have used this inversion method from the start of my developing career ( no pun intended) and has produced consistent results every time. Once you have found a method that works for you; you should stick to it.

The Thermometer.

This is one of the most important pieces of kit in the darkroom. As already mentioned temperature is one of the main controlling factors in the processing of your films and prints. It is important that you have good quality thermometers that are graduated to at least half a degree but a quarter of a degree is better and one that has a thicker line at the vital 20 degrees C. It is a good idea to have a thermometer for each of the chemicals you use in the processing of your films and prints as it will stop cross contamination.Also there will be no hold ups if you break one. It is recommended that you keep to one type, preferably alcohol as it is safer than mercury. If a mercury thermometer breaks it will contaminate the chemicals it comes into contact with and fog any prints that are being processed at the time.