Comments on the paper "Some investigations on the kinematics of the Ilford film washing procedure" by Rolf Suessbrich, part of

Marc Torzynski1
Laboratoire des systèmes photoniques
École nationale supérieure de physique
Université Louis-Pasteur
Parc d'innovation, BP 10413, F-67412 Illkirch Cedex, France

October 2004

There is certainly nothing wrong with the paper "Some investigations on the kinematics of the Ilford film washing procedure" by Rolf Suessbrich2. The description of the emulsion washing as a diffusion process is perfectly correct and experimental measurements are very convincing. When it comes to quantitative calculation, however, a complete estimation based on actual values should be done.
A 135/36 wet film holds about 4 ml of fixer solution, 2 ml of which being absorbed inside the emulsion, the remaining located at the surface of the film3. Drained, a 500 ml tank keeps about 6 ml of droplets along the walls and the cap4. Thus, there is a total of about 10 ml of remaining fixer, which corresponds roughly to 600 mg of thiosulfate5.
If after pouring out the fixer we simply refill the tank with 500 ml of water and wait for the absorbed fixer to diffuse out of the emulsion, we should end up with a residual thiosulfate level of 1.2 g/l (600 mg:500 ml), which is just slightly below the recommended archival limit of 1.5 g/l. Expressed in Suessbrich's units, the residual hypo level in water as well as in film will be "dil. 50" (10 ml:500 ml).
If the film is first thoroughly rinsed, the walls and the surface of the film will be clean and only the 2 ml of absorbed fixer will diffuse into the 500 ml filling water, lowering the residual hypo level to 0.24 g/l or "dil. 250"6.
In any case, Suessbrich's conclusion remains true: a single wash is theoretically sufficient. However, as he pointed it out, the time required to complete the diffusion process may be excessive because that process slows down as the hypo concentration difference inside the emulsion and the surrounding water decreases, thus preventing the reach of the equilibrium point.
Let us however carefully investigate the washing process and its dynamic from Suessbrich's data. From his Fig. 2, where a good wiping reduces the take over, it appears that after the first wash, a second and a third washes have almost no effect (as have no effect the additional washes of an already well washed film - see Figs. 5 & 6). Additionally, it can be seen from the shape of the curve that the first wash could be reduced up to 60"!
One could object that having relatively clean water does not mean that the emulsion is of the same cleanness. This is what Suessbrich points out by claiming that the binding mechanism of the hypo into the emulsion may prevent the reaching of the above computed equilibrium points using a single wash. Indeed, breaking that bindings may require a strong hypo concentration difference between the emulsion and the surrounding water, which is achieved by regularly replacing the used water by fresh one. But should such a breaking occur in these successive baths, it would be monitored by a significantly increase of hypo concentration in water, which is, according to Fig. 2, not the case: the lower curves show that only a minute quantity of thiosulfate migrates out of the emulsion in the 2nd and the 3rd bath.
I would conclude, in a rather iconoclastic way, that a good rinse and a single 1 minute wash in 500 ml of water with continuous agitation will leave the films perfectly clean.
Of course I won't really advocate for archiving the films after such a procedure, because there would be absolutely no safety factor left: a 2- or 3-wash procedure is certainly a safer figure. But this analysis embeds what Suessbrich suggests: the washing requirements are usually largely overestimated. In my lab, photographic films that were given no more than a one minute rinse have been stored for more than ten years without any degradation; the same is true for holographic plates, whose silver grains are 1/100 000th smaller than those of common B&W films and therefore much more prone to be "eaten" by residual fixer7.
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 minutes8 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 tank9. 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.

3This was measured by weighting the film dry, wet, and wet but wiped. It may sound astonishing that a dry emulsion volume of 0.6 ml absorbs 2 ml of liquid, but we should keep in mind that wet gelatin expands up to 10 times its dry thickness.
4This again is a measured figure.
560 g/l hypo is a common figure for film fixer at working strength.
6Actually less, because some hypo will diffuse out of the emulsion during the rinse.
7... and I remember having seen a well-washed film turning yellow in two weeks because it was forgotten near a big PVC roll whose chloride or solvent emanations quickly oxidize the silver : I am pretty convinced that most of the encountered film degradations comes from bad storage.
8Kodak washing procedure.
9We measured this by monitoring over time the decrease in concentration of a conductivity tracer introduced in the tank at the beginning of the wash.

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On 15 Feb 2005, 08:39.