For you chemistry gurus;

Given these formulas for sodium sulfide/selenium toners:
Dassonville T56 Toner
Chemical Amount
Water 100ml
Sodium Sulfide 25g
Selenium powder 5g

Flemish Toner
Chemical Amount
Water 750ml
Sodium Sulfide 40g
Selenium powder 1g
water to make 1000 ml

What would be the keeping properties of the stock solutions under optimum conditions?

Also, any guesses as to the differences in image tone, and how might varying the ratio of sulfide to selenium affect this?

Thanks for whatever wisdom anyone might have.