How your films are processed: film processing (part 2)
Welcome to the wonderful world of film processing. We saw few days ago what are the differences between negative, positive and b&w films. While the layers are slightly different, the most important thing for the labs is the process to use. In this part of our guide to film photography, we explain to you what are the different developing processes.
Black & white wonders
1 process – 2 steps
Let’s start with the oldest process listed today. And well, as the title shows it, it is used to process b&w films. The processing itself is divided in two big parts. The first part being the actual chemical processing of the film and the second one being the refinement of it. It seems pretty obvious, but the processing has to be done in total darkness. It is divided in at least three baths: developer, stop and fixer. So, let’s take a closer look at those.
A non standardized process
The composition of the developer bath varies according to the formula chosen by its creator. Thus, the composition of Kodak D-76 is not the same as that of Ilford Hc-110. As a result, the choice of the developer will have a significant impact on the final result. While some developers favour highlights, some minimize the grain, and others influence the contrast. You will find them in powder or concentrate to dilute into water. Although the composition varies a lot, you will always find three main chemicals: developing agents, alkaline agents and sodium sulphite. As its name indicate, this bath will reveal the image by reacting with the particles of silver halide exposed by the light faster than the unexposed ones.
After a certain amount of time, the developing reaction has to be stopped to prevent everything to turn black. This is when the stop bath is used. Made of acetic acid, the stop bath bloke the reaction and prevent any further development.
The third bath will “fix” the image. As you can see below, the fixer bath removes the unexposed silver halide remaining on the film. Because of the thiosulfate salt this process, the film will not react anymore with the light. Without this last step, the film could fog and destroy the photographs you just shot. After this step, all you have to do is to clean, rinse your film and hang it to dry in a dust-free environment!
The wonders of colour film processing
C-41 film processing
Unlike b&w films, most of colour negative films are made to be processed with a standardized process. The later was created and introduced to the market by Kodak in 1972. Nowadays, almost all colour films are made to be developed with the C-41 process. Processing colour negative films is a bit more complex than b&w films: developer, bleach, fix, wash and stabilizer.
Like any film, the developer bath will make the image appear on the negative, however, the composition for C-41 is not exactly the same. Also, colour films are usually processed in higher temperature than other films: 38°C vs 20°C. The chromogenic developer will oxidize by reacting where they have been received from the light. The bleaching eliminates this reduced silver. The oxidized developer will react and give light to the original film’s light, yellow, magenta or cyan colours. The final bath, the stabilizer, serves to prevent the film from undergoing any external degradation after its development.
E-6 film processing
When it comes to colour film, you have the choice between negative or positive film. The E-6 process is dedicated to latter. It is probably the most complex process of this list. A first b&w developer bath creates an image on each layer of the film. A first wash stops the reaction. A reversal bath prepares the film for the colour developer bath. The reversal agent enters the emulsion and prepares the unexposed, undeveloped silver halide for the chemical reversal that occurs in the colour developer.
Then, the colour developer is introduced. While it formes a metallic positive silver image, the colour developing agent oxidizes. This one reacts with the couplers and dye each layer of the film. After that come the bleach and fixing like in C-41. However the bleaching bath is divided in two in order to be more effective. The following steps are the same: washing and drying in a dust-free environment.
Although these are the most common and used methods, they are not the only ones. In a few weeks we will talk about the case of ECN-2 used for cinematic films such as Kodak Vision films. In the next article, we’ll show you the equipment your rolls are processed with! Stay tuned !