Black Crud

[RexWH]

What is the black scaling on the inside of my bottle of working strength Kodak Rapid Selenium Toner?

[Jim Galli]

What is the black scaling on the inside of my bottle of working strength Kodak Rapid Selenium Toner?

Silver.

[Ole Tjugen]

Silver.

Silver selenide, more likely - since selenium toner is supposed to react with silver to form silver selenide. :)

[Gem Singer]

Pass the selenium toner through a coffee filter to remove the black precipitant.

Working strength selenium toner can be replenished with fresh concentrate and reused over a long period of time.