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Many people wonder how sepia toning of black and white prints is done in practice. We have carried out some tests in the darkroom, toning various kinds of paper in Kodak's sepia toner. Sepia Toning black and white prints Many people wonder how sepia toning of black and white prints is done in practice. We have carried out some tests in the darkroom, toning various kinds of paper in Kodak's sepia toner. Sepia toner is, as its name suggests, tones a print brown. The key active chemical is sulphur, a fact that is hard to miss because the toner smells vile. Sepia toner, in common with most other brown toners, is a two-bath toner. The print is bleached until all or most of the image disappears, and is then redeveloped until it becomes brown to a greater or lesser extent. Bromide paper or bromide chloride? The agents that make photographic materials sensitive to light are silver halogens. Those most commonly used in photographic papers are silver bromide and silver chloride. The emulsion of a photographic paper contains either silver bromide on its own or a mix of silver bromide and silver chloride. After development, silver chloride has finer grain than silver bromide. The fine-grained silver is more easily affected than the coarser bromide silver. Photographic papers with a high proportion of silver chloride are warmer in tone than the silver bromide papers. A simple way of finding out if your paper contains silver chloride is to tone it in selenium. If it turns brown it's a silver chloride paper, whereas the pure silver bromide papers do not. If you want a deep, rich, brown tone you should pick a paper containing plenty of silver chloride. It will tone faster, and acquires a saturated brown tone after only a short time in the toning bath. The toning process Kodak Sepia toner is sold in one litre kits that consist of two bags of powdered chemicals, each of which should be dissolved in approximately one litre of water. The first solution is the bleach bath, the second is the actual toner. The kit is good for about forty 18 x 24 cm prints. The actual toning is easy to perform and can be done in daylight. As always, you should work with well fixed and well rinsed, wet black and white prints. Because heavy sepia toning tends to make prints lighter than they were originally, it is advisable to make a darker print than you normally would. Dry, finished prints should be given a thorough pre-soak in water. The print is first placed in the bleach bath and agitated constantly for two to eight minutes. The kit recommends five to eight minutes, but it is perfectly possible to use shorter times. You should wear rubber gloves because the bleach can be harmful to your skin. The longer the print is in the bleach bath, the paler the picture. There is room for experimentation here: I recommend toning several identical prints, varying the time so that you have several different degrees of toning to choose between afterwards. After bleaching, the print should be rinsed in running water, to remove all residues of the bleach from the paper. Two minutes is a reasonable rinse time. The picture should then be transferred into the toner where it is re-developed very quickly and turns brown almost instantly. The whole process takes only thirty seconds. The picture should then be rinsed to remove all residual toner. I recommend a thirty-minute rinse. According to the instructions that come with the kit, prints should be hardened after toning. This only applies to pictures that have been fixed with a non-hardening fixer. Most pre-mixed fixers contain a hardener, so separate hardening is unnecessary. If you use a simpler thiosulphate fixer such as Kodak F24, you should harden the prints yourself. Kodak sells a suitable hardener. Improved archival properties One problem with prints is that we do not know how long they will last. Everybody at some time has seen a black and white picture that has turned partially brown with age. This is called bronzing. The silver in the print forms a compound with another chemical, usually sulphur. Since the picture is supposed to be black and white, and bronzing is irregular, the picture can be regarded as ruined. The problem in long term storage is that the pure silver in the prints reacts easily to form compounds with other chemicals, leading to changes in colour. After toning in a sulphur toner, brown silver sulphide is formed. Silver sulphide is much more stable than pure silver, and a sepia-toned picture therefore has a much longer archival lifetime than an untreated print. Lars Kjellberg |
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