Traditional silver halide papers, especially fibre-based varieties, potentially have an extremely long life – maybe 200 years or longer. Archival processing maximises this by tightening up standards of fixing and washing and maybe adding a toning stage, to ensure the maximum longevity of the final processed print.
Fixing takes place in a series of chemical changes;
the first fixation product is almost insoluble in water, and is then converted into more soluble products, but the second conversion ONLY takes place if there is excess fixing salt available.
So there needs to be plenty of free thiosulphate, one reason for not taking the fix bath to exhaustion. Another complication – insoluble silver-thiosulphate complexes creat- ed will build up in the paper structure and fix solution, and at a certain level these will bond onto the paper fibres. One approach is to process only a relatively small number of prints through a fixing bath, and discard it when it has reached a specified silver level, a safe level being 0.5 grams/litre. This can be checked with silver estimating strips. Ilford’s ‘Galerie Sequence’ is a refinement of this approach (previous page). An alternative method is to use 2 bath fixing. The first bath performs most of the work, taking the print to stage 1, and the second fresh bath ensures that all the silver salts are rendered soluble. When the silver level of the first bath reaches a safety threshold (2 grams silver per litre) it should be discarded, replaced with the second, and a new second bath made up.
Hypo Clearing Agent
This is a bath used after fixing to assist in washing out fixer and its products by ion exchange, and can help achieve a lower thiosulphate level than washing on its own can manage. It also considerably improves washing efficiency when using cold water. Hypo clearing is highly recommended, being cheap, quick and effective.
Normally in a Selenium Toner, which forms a silver-selenium compound which is more stable than the original silver image. There is also a subtle intensification, and a clearing of ‘oliveness’ which generally results in enhancement of the print quality.
Suggested dilution of the Kodak product is 1+12 with water. A stronger concentration will result in much faster action, and a rapid colour change with warm tone papers. Colder papers (e.g. ‘Fomabrom Variant’) react less rapidly, but selenium toning is still a very useful treatment for the slight expansion of the tonal range through the deepening of the maximum black, and the improvement in permanence. Another type of toning particularly useful for permanence is Gold Toning, which does not give a gold colour, but shifts the image tone towards a subtle blue (red/orange on a previously sepia toned print). Sepia toning, although a good permanising treatment substantially shifts the colour of the print and is therefore not generally appropriate.
Preferably in a washing system that keeps prints separated and passes a consistent stream of fresh water over them. Washers holding prints vertically in separate slots are better at achieving this, so tend to be called ‘archival washers’.
Extra Care in Drying
‘Air-drying’ ideally, since nothing comes into contact with the wet print which can contaminate it, eg the canvas aprons on heated dryers.