Selenium Toning
A treatment that converts silver to silver selenide, deepening blacks and giving prints a subtle cool or purplish shift.
Measured in
dilution ratio
In depth
Selenium is used more for permanence and density than for colour: dilute solutions leave the tone almost unchanged while measurably increasing maximum black and archival stability. Stronger dilutions and longer times shift warm-tone papers toward reddish-purple. It is toxic and needs good ventilation.
Examples in practice
Two minutes in 1:20 selenium raises a fibre print's maximum black noticeably without any visible colour change.