See the other thread on bleaching re: the so-called dangers of potassium ferricyanide. There seems to be quite a bit of needless worry about this chemical. Unless you dump a bunch of it in concentrated nitric or hydrochloric acid, you are in no danger from this chemical. You probably are exposing yourself to more dangerous stuff in the metol and hydroquinone in most developers.
Originally Posted by Andre R. de Avillez
If you want a really easy to control warm tone result, I recommend a homebrew thiocarbamide sepia toner on cold tone paper. There is a great discussion of how do this on Wynn White's website. It is cheap to mix yourself and gives very nice warm purple brown results on most cold tone papers if you use the higher concentrations of NaOH