Tuesday, 8 January 2013

Black and White Film Processing: It's All In The Wash

Black and white film photography is still popular around the world and new generations of amateurs and professionals are learning the black art of film development, albeit with a greatly reduced range of commercial products. Those of us who started processing our own films in the mid-1950s will have been surprised over the years as the advice on washing films after fixing changed. We were brought up in the wash the film in running water for 30 minutes school. However, the success of our fixing and washing methods is evident. None my negatives from that time has deteriorated.

The Complete Photobook by Philip Johnson (Fountain Press, London, 1955) was an excellent introductory book to photography. Johnson wrote:

     ...washing for 30 minutes is necessary in order to remove all trace of fixer and soluble silver. If this is not done, the negatives will deteriorate, and processes such as reduction and intensification become hazardous.
     Simply placing the tank under a running tap seldom gives a steady change of water round the whole film; indeed the inner coils towards the base are barely affected. Unless you are prepared to empty the tank completely (removing the lid) and refill with fresh water at least 8-10 times during the 30 minute period, with regular agitation, the tap-water must be led into the centre hole by a length of hose acting like an inverted fountain through all the coils of the film. Washing is carried out in this manner by the Polly film washer, a neat little device which is available for use with up to six tanks at once by means of simple adapters.
     Note carefully the temperature of the wash water, especially at the start. Any sudden change in it subjects the gelatin emulsion to great strain, and it is then apt to split into minute cracks. This is known as ‘reticulation’, for which there is no cure; so, if it is not possible to have running wash water at 65-70°F, gradually reduce the working temperature by several successive changes, each two or three degrees cooler until it is the same as the tap water. If this is below 60°F, washing time must be increased by 10-15 minutes, but avoid the necessity if you can.
An illustration from The Complete Photobook by Philip Johnson,
Fountain Press, 1955

In the 1950s and 60s, my grandfather, father and I followed this advice on the 30 minutes but ignored the advice on temperature. Films went straight from the fix into water at whatever temperature it came out of the tap. We never had a case of reticulation. We did not wash for 45 minutes at tap water temperatures below 60°F (most of the year in U.K.). I did however, make one change. I reasoned that it was easier to get rid of most of the hypo quickly by emptying and filling the tank a few times before connecting the ‘inverted fountain’ to finish the job. I repeated this procedure after I turned the fountain off.

Everybody I knew washed films for 30 minutes. However, that advice was not universal. Lancelot Vining, in My Way with the Miniature (8th edition, 1947, Focal Press, London and New York) wrote:

When your films “go wrong” after drying and storage, it is mostly not, as so often supposed, from insufficient washing, but from imperfect fixation. After fixing wash for five minutes in running water, then harden, and back to running water; five minutes in this is ample.

For some, however 30 minutes was still not enough. Werner Wurst’s Exakta Manual (2nd English Edition, 1966, Fountain Press, London) stated 45 minutes.

In some parts of the world (certainly not ours) water supplies are restricted and expensive. In the 1970s Ilford came up with a radical change in recommendations for washing film after fixing. Just three changes of water, with increasing numbers of inversions of the tank for agitation at each refill. They claimed archival quality for the negatives produced. Participants in internet fora have stated that they have stored resulting negatives for 10 years without ill effect. It is important to note that the Ilford method is for non-hardening fixer. Other film manufacturers continued to recommend running water, often for 15 minutes. An advantage of the Ilford method is that it is easy to keep 1500 ml of water at approximately the same temperature as the developer and fixer and therefore avoid the possibility of reticulation of the gelatin on sudden exposure to cold tap water.

From Ilford Technical Information. Rapid Fixer.
Harman Technology Ltd. July 2010

There has been some scepticism on the efficacy of the Ilford method and a number of photographers have made crude chemical measurements (with and without hypo eliminators after fixing) and theoretical calculations to test whether or not they should use and recommend it. I show links to some of the websites discussing film washing at the foot of this article.

The object of washing after fixing is to reduce the residual hypo concentration in the tank and emulsion and to reduce the concentration of silver-hypo complexes in the emulsion to a level at which these chemicals will have no deleterious short- or long-term effect on the developed image. The term washing or rinsing is a misnomer since the key factor is diffusion of the silver-hypo complexes out of the emulsion.

If diffusion were not involved, it is easy to calculate the effect of emptying and refilling a developing tank. For washing laboratory glassware we were always taught to fill and empty the container with its own volume of double-distilled water three times. The dilution of any remaining chemical in the vessel would be so great that effective freedom from contamination could be assured. Let’s use Marc Torzynski’s figures (link is shown below) for a 500 ml developing tank but assume that all the fixer still present (10 ml) is just in droplets on the walls of the tank and on the film. In the first wash, the concentration of fixer is 10/500. Then, again let’s say 10 ml is left behind so the concentration in the second wash is 10/(500x500), and on to the third wash where the concentration is 10/(500x500x500). That 10 ml of fixer is now just 0.00000008 ml; instead of 600 mg hypo in the tank, there would be just 0.0000048 mg after the final wash

However, diffusion is involved. Diffusion in a gelatin emulsion is much slower than in water. The rate of diffusion out of the emulsion depends on the difference in concentrations of the silver-hypo complexes and the free hypo in the emulsion and the concentrations in the surrounding water. Therefore, the more often the washing water surrounding the emulsion is replaced, the faster will be the rate of diffusion. Agitation is important because it replaces the water into which silver-hypo complexes and free hypo have diffused from the emulsion by water containing a lower concentration. In processing films, the purpose of agitation is to prevent the formation of what physiologists call unstirred layers and physicists call boundary layers at the emulsion surface both to let fresh developer, fixer — and water for washing — reach the emulsion and its inner structure.

The concentration gradient is not the only factor determining how fast diffusion from the emulsion will be. In the classical equation (Fick’s laws of diffusion) the concentration gradient is multiplied by a diffusion coefficient. The diffusion coefficient, in turn, depends of temperature (hotter faster), viscosity (gelatin has a much higher viscosity than water) and the size of the diffusing particles (larger particles are slower).

From the crude experiments that have been done, it would seem that diffusion of silver-hypo complexes from the emulsion into water is sufficiently rapid for the Ilford method to work. However, I would, as some photographic chemists have suggested, add a time element as well as an agitation element to the procedure, by leaving the tank to stand for a minute or so after the agitation step. I suppose that Ilford did add a time element in a way, since slowly inverting a tank takes a finite amount of time and the increasing number of inversions with each change of water does increase the time available for diffusion from the emulsion.

Incidentally, in a recent video that has appeared Youtube showing beginners how to develop film, agitation by inverting the tank is shown as a rapid process — almost a shaking action. Rapid agitation at any stage of the development process carries the danger of creating air bubbles on the film that may block the access of developer, rinse or fixer. A slow, deliberate action of inverting a conventional vertical tank is all that is needed.

All the experiments I have seen have been pretty crude and have measured the appearance of products in the wash water, not what has been left behind in the emulsion. Those are experiments I would like to see the results of before abandoning pre-Ilford recommendations on washing after fixing. I would also like to see how Ilford decided what archival quality is and whether, as some correspondents have suggested, 10 years of non-deterioration is a reliable indicator that a negative will last for 100 or more years.

However, at the moment, proponents of the Ilford method seem to hold sway. Marc Torzynski of the Laboratoire des systèmes photoniques, École nationale supérieure de physique in France who, in 2004, concluded by saying (in a translated version of his paper):

In my opinion the photographers community has developed over the years a false but very obsessive position according to which a proper washing cannot be achieved without leaving the film plenty of time under a waterfall. And even the reasonable common suggestion of washing the films for about a quarter of an hour under a running flow which allows a complete change of water in the tank every five minutes (Kodak washing procedure) is a waste of water compared to Ilford's method, because this 5' change rate requires a water flow of at least 1.5 l/min for a 500 ml tank (we measured this by monitoring over time the decrease in concentration of a conductivity tracer introduced in the tank at the beginning of the wash). It was a therefore a pleasure to read Suessbrich's paper, which I hope will help to break all these generally accepted but preconceived ideas about washing.

With the benefit of hindsight, it appears that Lancelot Vining, who started his career as a photographer in the 19th century and was a regular columnist for Amateur Photographer, was nearer to this mark than standard thinking of the day. My grandfather, who read Vining’s column avidly but who never bought his book, would have been delighted. Had he bought his book, the films from his Zeiss Contina would have had 5 minutes wash, a hardening bath and then another 5 minutes. Vining’s word was law.

So, what will I do when I have to develop some Ilford films in the next few weeks. Will I stick to my old routine or follow the evidence and go all modern?

The first decision, though, is whether or not to use a hardener in or after the fixer. Ilford’s recommendation is that modern films do not need a hardener unless processing at high temperatures. With a hardener (which will change the structure of the emulsion and increase diffusion coefficients) I would do several changes of water and continue under running water for 30 min; in other words, the old routine. I will not use a hardener.

The second decision is whether to use a hypo eliminator. No, I am not in a hurry and the eliminator itself needs to be washed out.

So how long to wash for? Well (always a useful start for indecision), I still have have a slight nagging doubt on whether a short period is adequate for the diffusion larger silver-hypo complexes. I think I will follow the Ilford procedure but extend the number of refills to, say, 8 over a period of 10 minutes or so. Belt and braces approach? Yes, but we have so much  water that we could probably sell you some (bottled, perhaps, as Ayrshire Film Washing Water).