Brown toner is a strange one to cover here, as at present there is no commercial article available to purchase! However it’s such an interesting & useful toner that it’s worth a section of it’s own. Brown toner has always been made from the complex sulphur compound potassium polysulphide, generally called ‘liver of sulphur’.
Liver of Sulphur is the alchemists’ name for a chemical mixture produced by heating potassium carbonate with sulphur, made as long ago as 776AD by the celebrated Arab alchemist Jabir Ibn Hayyan. It is not a true compound but a metastable mixture of potassium polysulphides and potassium sulphate. (K2S, K2S2, K2S3, K2S4, K2S5, K2SO4). Since the end point of the reaction used in liver of sulphur production varies from batch to batch, the exact constituents of the product also vary as well.
Difficult to find from normal chemical supplier, but easier to locate from suppliers to the jewellery industries, where it’s used for producing a patina on metal surfaces.
No bleaching is required, the well washed print is simply immersed and in a few minutes when almost 100% of the silver has been converted to silver sulphide, a warm brown image will be the result. The downside – brown toner evolves hydrogen sulphide (bad eggs) which is not good for film and paper, although when used at high dilutions this should not cause a problem.
It is particularly good for warm tones in combination with Ilford Warmtone Multigrade. Partial convertion will show little or no colour change, although the permanising effect is still active, and a strange property is that conversion is speeded up as dilution is increased, and the toner becomes more exhausted. Consequently, this type of highly active polysulphide toner can give complete protection even when used at 1+200 dilution. One authority recommends a time of 1 minute at a 1+50 dilution, which will convert approximately 75% of the silver to silver sulphide, leaving no colour change. This is not dependent on density, so the image will not ‘split’ like selenium.
Although there has been much research, and the evidence for the effectiveness of polysulphide is beyond doubt, it remains curiously unknown to the wider photographic public.
You might still occasionally be able to find the last manufactured article, Agfa Viradon.
Another was at one time available from Kodak, called just ‘Kodak Brown Toner’.
The Strange Case of the Temperamental Toner
Lee, Wood, and Drago published a paper in 1984 dealing with the stability properties of a variety of toned images and found selenium acted very well as a protective treatment However when the Image Permanence Institute at Rochester Institute of Technology delved further into the action of selenium they found that although selenium worked well for high density areas (shadows), it did not convert the mid-tones and highlights that well, contrary to general opinion.
When this was referred back to Kodak, they went back in their records for formulations and chemical sources. Prints produced by practical users in the field had unusually stable prints, but this stability was not supported by lab tests, which showed a much lower level of resistance to oxidants. It was some time before they realised that there was a difference in the make-up of the chemistry; the consumers were using selenium toners made from GPR chemicals (general purpose reagents) while lab experiments were being done using analytical reagent grade chemicals (very high purity.)
It turned out that sodium thiocyanate in the consumer toner was made from practical grade chemicals contaminated with a number of active sulphur compounds, while the high purity analytical grade chemicals contained no sulphur. Consequently, the action of selenium as a permanising agent was revealed to have been seriously over-rated, and those of sulphiding agents need to be re-assessed. This is indeed taking place, and most institutions involved in photographic conservation are now recommending some form of polysulphide toning rather than selenium.
Kodak T8 toner
Potassium Sulphide: 7.5g
Sodium Carbonate monohydrate: 2.5g
Water to make: 1 litre