Hey dan, once the selenium and silver have combined in the print, it's a fairly benign substance that's left in the print (e.g. converted silver) - it still needs a good wash though as the selenium toner contains hypo, so another archival wash is needed, probably using a wash-aid if you want to reduce water usage. . And the used toner, provided it is mostly exhausted, makes for excellent fertiliser for your non-food garden plants. I exhaust mine by leaving waste prints and test strips in it over night.
if you want to force a colour shift with mgiv and selenium:
1. buy a thiocarbamide toner kit (variable sepia),and make up a weak dilution bleach bath from the kit.
2. make a print on the mgiv and over-print by about 20% or more.
3. bleach this print until the highlights and most of the mid tones are nearly gone. (wash thoroughly)
4. place in a selenium toner made to between 1:5 and 1:10 and allow to re-develop.
5. wash thoroughly again.
If you get your printing and bleaching and timing right, you'll get a pleasant yellowy brown in the highlights and mids split against a cool steely blue in the shadows and lower tones. here's one of mine ising this paper and toning technique - hopefully the print values will carry on the screen:
