Selenium Toner

Selenium toning actually lays a coating of selenium (which is a metal) on top of the existing silver emulsion, and in the process gives the emulsion a physical protection from pollutants and contaminants. It can be mix to either give only a protective coating or mixed to give the protective coating and a colour change. It is generally acknowledged as a superior means of preserving the image than sepia toner.

When mixed to cause a shift in print colour, the results can be variable and sometime frustrating. They can vary from a cool black tone to a red brown Selenium is inexpensive and permanent, but is a poisonous substance and should be handled with care. 

Protective Coating only
For this a selenium solution like KODAK Rapid selenium Toner is diluted 1-20 with water. The toning should take over a few minutes and depending on the nature of the paper will show as a faint change in the density of the print. For those who whish to experiment the following recipe may be of some use. 

Water to make                  1000ml 
Sodium sulphite anhydrous   200grms
Selenium                    30grms

Remember there can also be an increase in contrast and the prints can look quite different when dried down, with some of the richness lost.

Combined protective/colouration Coatings 
Selenium can also be mixed 3-9 parts to obtain not only protection, but a colour shift. Here the affects of selenium can be quite variable and depend greatly on the paper type. Ilford for instance seems to have only a slight shift to a darker blue, while some Kodak and Agfa papers produce quite red/brown and purple colours. Other factors like developer type temperature etc play apart. Complete toning may take up to 20mins and depends on the temperature of the solution and the concentration.

Split Toning with Selenium
Using the concentration (3-9parts) to create a colour change, a print can be obtained with a separation in the tones. Unlike other toners that affect all parts of the prints simultaneously, selenium tones drome the dense areas of the print to the lighter areas. With experience and careful control the process can be halted at a point where the tonal change is SPLIT. Here the darker areas take on a red/ purple tone while the lighter areas take on a more green colour. The complete image has a protective coating but the colour change is only allowed to reach the denser areas of the print. The effect can be quite subtle although rich and stunning. 

Wash
Selenium toned prints should be washed for 60mins after toning.