Tars, I start with a double 1% solution, i.e., 1g ferricyanide and 1g bromide per liter. I keep solutions of both on hand: a 10% ferricyanide solution and a 3.4% potassium bromide solution. I make a liter of bleach by starting with 10ml of the ferricyanide solution and 30ml of the bromide. (For local bleaching, I mix up smaller amounts in the same proportions.) This is rather weak, and I don't hesitate to add more of both if needed; its very subjective.
Originally Posted by tars
As for toning: I have found that heavily bleached areas can selenium tone differently, but that it depends on the paper many times just what happens. I try to avoid bleaching really heavily and tone lightly when I think I might have problems (by that I mean toning a long time in a weaker toning solutions so that I can pull the print quickly if I notice any change in toning from bleached to non-bleached areas. I also time the bleaching so that I can avoid the split-toning in subsequent same prints.).
Toning will almost certainly be different if you overbleach and then return the print to the developer to save it. Tone very lightly if you do this.
If you just use ferricyanide alone, the bleaching will be slower. Often, you need to help it out a bit by adding fixer, in essence, making Farmers reducer. Sodium or ammonium thiosulfate will both work, but the ammonium thiosulfate reacts a lot more strongly with the ferricyanide and is often harder to control).
I used to bleach right after the first fixing bath with plain ferricyanide; the amount of rinse I gave the print before bleaching controlled the amount of fixer still remaining in the emulsion and, therefore, the activity of the bleach.
Bleaching is an art and takes experience, but is a great tool. If you are just starting out, be prepared to ruin some prints in the learning process. I still ruin some, but I consider bleaching a print manipulation, and I toss a good number of prints with inadequate dodgine, burning or exposure too.