Mysteries Of The Vortex (Part Two)

Test 8: Washing using minimal volume of water

This was done to make an empirical check on what might be regarded as the bottom line for achieving a good quality wash. Specifically, what is the minimum volume of water that can be used to produce an archival wash, using no drainage or replenishment? A starting point was to consider a single tank of water and the quality of wash that can be achieved using simply this one volume. First, disregard the residual hypo in the wash water, and remember what we are looking for is a satisfactory level in the paper. It’s easy to forget that the paper is holding a relatively small amount of hypo that’s going to be diluted into a considerable volume of water.
The effect of effluent fix in the wash tank is usually cited as having a major influence on the wash quality, and that effluent fixer held within the wash chamber is a serious retarding factor to the later stages of the wash. This is the reason for usual recommendation for the usual high level of water turnover.

If a dump/refill system is not being used, what is the significance of this presence of this residual thiosulphate in the water, which is being progressively diluted as the wash proceeds? The actual thiosulphate present in the print can be calculated by working back from the fixer carryover. When removed from the fixer, the dry weight of a 16 x 20 sheet (62g) has increased to 85g, so it is carrying 23 grams, and therefore in volume 23 millilitres, of fixer. Relating this volume to litres (1000/23 = 43.48) gives a figure for comparing the known thiosulphate concentration.

Ilford Multigrade Fixer (again, Hypam to UK readers), in its concentrate form, contains 650 grams of ammonium thiosulphate per litre. Working strength fixer at 1+9 (Universal Rapid equivalent dilution is 1+6) therefore contains 65 grams per litre. From molecular weights we deduce that the thiosulphate content of the chemical accounts for 76% of the total, so the weight of the thiosulphate is 49.40 g.

49.40/43.48 = 1.136 g thiosulphate ion per 16 x 20 print, equating to a level of 5.51 grams per square metre. A 16 x 20 print has a volume of 60ml. If we place 10 of these prints into the washer, we are introducing 230ml fixer into the 50 litre tank. If these prints are washed in one single tank of water until equilibrium is reached, a ratio is established of 50,000/230 = 217.39.

This equates to a final thiosulphate level in the print of 5.51/217.39 = 0.0253 grams of thiosulphate per square metre. While hardly qualifying as outstanding, this level would equate to just below point 2 on the Kodak Hypo Estimator, acceptable as a commercial level of retained thiosulphate. What this means is that a commercial standard should be attainable in an archival washer with no exchange o water at all.

Test 8 was carried out to see if the theory predicts the practical result. Although a 12 x 16 tank was used, the ratio of volume to format is similar.
Ten sheets of Ilford Multigrade Fibre Base paper were processed through Ilford Multigrade Fixer at 1+9 for five minutes, and then given a very brief pre-rinse in a tray of water. They were then loaded into the Nova 12 x 16 washer filled with fresh tap water, and agitation produced by lifting each print in the slot and lowering it back in turn throughout the sequence. The results seem to confirm the hypothesis. A plot drawn from the densities follows the path of the running wash closely, and the thiosulphate level bottoms off at a stain density of 0.11, which indicates a thiosulphate level of about 0.035 g/m2, equating to the midpoint between Kodak Hypo Eliminator patches 2 and 3, and coinciding reasonably well with the theoretical calculation. Repeating the single tank wash with a hypo clearing step achieved an even better result (only marginally inferior to the control running water wash Test 1 without an HCA step) and delivering a final figure of about 0.02 g/m2 thiosulphate. The shape of the single tank plot does not deviate from the running wash control, and actually levels off quite early on at about 20 minutes. This seems to contradict the retardation school of thought, and to confirm the importance of agitation.

Although this result is interesting, it does not imply a recommendation to turn the tap off—in practice, the absence of agitation due to water entering the washer would significantly slow the time in which equilibrium could be achieved. But it is worth bearing in mind as the bottom line requirement for acceptable washing and, if agitation were applied mechanically or by re-circulating the water, even with limited exchange, it would be quite viable as a practical washing method. It shows it is possible to wash to an archivally good standard in only one tank of wash water with no addition, drainage or exchange, as long as the tank is sufficiently large. This also indicates why a wash based on exchanges of water rather than running water can be effective, and why washing regimens which alternative agitation with still water soaking also work well. This result has especially far-reaching implications for darkroom workers who want to use fibre paper but who live in areas where fresh water is in severely short supply [see “The ideal archival washer (yet to be manufactured)” under “Conclusions” below].

Test 9: Test of smooth vs. textured dividers

Nova very kindly made up some completely smooth dividers for testing purposes. To get some idea of the importance of the makeup of the cell walls, I used whole sheet silver nitrate testing as detailed in the Appendix. HT-2 spot testing could be compared to looking at a landscape through a keyhole—testing the whole sheet is like suddenly having the door opened. It’s also educational, in that sloppy technique shows up like a beacon: there was such an incidence of heavy stains due to traces of hypo on my fingers that I stopped and redid the series with fresh vinyl gloves for each print. [This should be a considered warning to us all—Ed]

The results appear to bear out findings from previous tests. The five minute test with standard textured dividers shows the level of stain as in Test 1, but this is quite uniform, marginally better across the bottom, which was in the stream from the inlet jet. The smooth divider shows more variation, and this is made more apparent with the 10 minute sheets. The sheet washed with the textured divider is washed quite evenly, while that from the smooth divider shows one area washing well while most of the bottom of the paper is giving a high stain level. This trend continues. At 20 minutes the sheet from the textured cell is clear of stain, while that from the smooth cell is still showing uneven stain densities, albeit becoming much lighter. At 30—40 minutes both types of divider were showing consistent even-ness. This problem seems to be associated with the emulsion side, presumably because as well as washing inherently more slowly, but also because, being smoother, it is more likely to adhere to a smooth divider. The pattern of mottling seemed random, but more tests need to be made to see if there is an underlying trend. A paper hardened during fixing is even more likely to wash unevenly in a washer with smooth dividers.

Of course, two cells in a standard Nova washer inevitably have smooth surfaces—those formed by the side walls of the unit itself! As suggested above, whenever possible, place the emulsion of the paper to the textured or most highly textured wall. If not fully loading the washer, leave the cells empty.


Test 10: Efficiency of soft vs. hard water

Extremes of hard and soft water were used as specimens. The soft side was provided by collected rainwater, which showed a pH of 4 (acid) while the hard water used was Scottish spring water called Glencairn Spring, which has a marginally acid pH of 6 and a composition, in mailgrams per litre, as follows: bicarbonates 81, sulphates 9, nitrates 3. The paper used was the same Ilford double weight MG FB, cut into 3” squares and fixed for five minutes in a 1+4 Multigrade Fixer and washed with semi-continuous agitation in 500ml quantities in trays, the water being replaced at 10 minutes intervals. For maximum density discrimination, blue filtration was used in the densitometer readings. The results were startling, showing a significant difference in the effectiveness between the samples. At the end of one hour the hard water had produced a thiosulphate level 0.01 g/m2, an acceptable archival standard. By comparison, the soft rainwater got off to a slower start and maintained its separation—at one hour, the reading showed a level of 0.02 g/m2, which is a barely commercial level.