I had created some prints last year from one of the rolls, the one taken in 'Sketchsters' bedroom studio set up. Printed on warm tone fibre based Ilford paper, the selenium reacted with the paper very nicely. Selenium is a heavy metal, it basically is used for its archival properties, adding 200 years or so to the print this chemical is also very poisonous and is not to be breathed in, I also had to wear gloves. The toner reacts with the black in the prints and ripens them slightly.
I did a test with a scrap print that was good enough to use. I was using, "Kodak Rapid Selenium Toner for Films and Papers". I mixed it up 1 part toner + 6 parts water. So 200ml toner and 1200ml of water, creating 1400ml of liquid overall, which was plenty for about 10 prints before the chemical depletes. I saved it after the use I had out of it though, there will still be life in it after 3 or 4 prints. I cut the scrap print into 4 pieces when it was dry and then soaked it in running water for 15 minutes or so, just to loosen u all of those fibres and allow any fix or other chemical to fully wash out. The four pieces were then put into selenium and each taken out at 1 min, 2 mins, 3 mins and 4 mins. This allowed me to see all of the stages of the toning visually, and this would allow me to understand the times needed using that specific paper at the specific chem strength. My final result was 3 minutes in 1+6 dilution, this gave the blacks a very slight richness and just crisped the edges up.
I also toned a Resin based contact sheet from the other day also and this came out nice but I dont like the deep purple in the black on the contact sheet, they should be completely black.