Going back a few years we did a very in-depth assessment of archival print washing, which was taken seriously enough by the US magazine ‘Photo Techniques’ for them to run it in 2 parts – copies of both are downloadable as PDF’s from the Articles section.
One of the things we checked out was the relationship of hypo clearing to washing efficiency. Ilford did a lot of work on this some years back, and came up with their ‘Galerie Archival Processing Sequence’. The key to this is fixing time – rapid fix more concentrated than normal, and so short (30 seconds) that it fixes the emulsion without penetrating the core of the paper to any extent. (Ilford later extended their recommendation to 60 seconds of fixing, as 30 seconds is rather impractical). After a 5 minute wash, which shifts a substantial amount of the hypo, there is a 10 minute Galerie Washaid bath, followed by another 5 minute wash – see top sequence opposite. Ilford later adapted the sequence to include selenium (lower sequence).
The dramatic effect of the Ilford Galerie Washaid sequence can be seen here in action; these graphs were derived from density
measurements made on stains on FB paper using HT2 solution, (acidified silver nitrate).
Graph A is a normal curve for dissipation of hypo from a fibre based print, after regular fixing for 5 minutes, and washing in one of our archival washers. Residual hypo flattens off after about an hour of washing, and even with hypo-clear is still measured to be falling 90 mins. into the wash.
Graph B shows the residual hypo under the same washing conditions after employing the Ilford recommended 60 second fix time in concentrated fixer, followed by hypo clearing. The drop in thiosulphate, and hence washing efficiency, that we found after using the short fix time was dramatic. Within a few minutes the residual hypo was virtually unmeasurable. In fact, we had to ‘turn up’ the sensitivity of the test by measuring the yellow silver sulphide stain with a blue filter on the densitometer.
A point here is that although the Ilford sequence is undoubtedly very effective from the point of view of time efficiency, it’s a rather hard taskmaster in practice. But the significant factor is the 60 second fixing time, and that can be employed in whatever way suit your work. The fix stage then becomes simply an add-on to the print development – get the print through the short fix step, and then keep the prints in a holding water bath until ready to wash the batch.