Stop not buffer.



One of the most popular over the counter acid stops.
Made from citric acid with colour indicator.

Stop is the second part of the development process, but how many of us give it a second thought. Most of us when we come to developing our first film tend to do what the manufacturers, friends and teachers suggest without delving into what the relationship is between these elements in the process. There is nothing wrong with this approach we are all eager to get on and see those all important first images. With success, we continue settling in to a way of doing things that produce good results. It's not until we start printing that some faults with the negatives rear their heads. Dust and hair marks being the most common but then there are those odd black spots appearing in the skies here and there. This is when the controversy about how we stop the development process comes to the fore.

There are two main categories. The more aggressive with chemicals and the gentler water stop. The later is not a stop and it is misleading to call it such.   It dilutes the developer to the point where it no longer has an affect on the emulsion this can and does lead to unevenly developed negatives and I cannot understand why it is recommended (for film only) other than to increase the longevity of the fix, a buffer or as a way of creating a certain style to the negative. 

Have been processed using a citric acid stop.

I personally prefer the more aggressive chemical route, when the stop go's in, the developer is stopped in its tracks producing a clean crisp negative but you need to be careful.

A popular choice in the make up of developers is Sodium carbonate, an alkali. When this comes into contact with an acid based stop it produces carbon dioxide gas that leads to blistering of the more sensitive film emulsion,( not the case with enlarging papers). It manifests its self as a pinhole in the denser areas of the negative. There are ways around this by using developers that are formulated from mild alkalis either balanced or borax which do not produce the damaging over heating or gas when used with acid stops.

A reflection of St Pauls in London.
Processed and printed using all Ilford products

Stops are made from several different acids the most popular is acetic with a pH dye indicator. The others are citric and boric. You can also use a simple solution of sodium bisulfite. Be careful which stop you choose as some produce green staining with some enlarging papers. Another precaution is to use the stop bath at a lower working temperature to the developer; I know this is a controversial move but I have used this method for years without any of the problems suggested by others.

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.