Starting point for bleaching back neg with potassium ferricyanide

[Akki14]

What sort of dilution do I need for bleaching back a negative with just potassium ferricyanide? Will refixing the negative in rapid fix be okay or will it do some harmful/bad reaction?
I got a box of c.1968 HP3 4x5 sheet film and it has some heavy base fog... after searching around on here I read someone uses potassium ferricyanide to bleach the negative back to counteract base fog but no one ever says how much or a formula or starting point. I'd need enough liquid for a 10x12 tray so about a litre will do.

Picture of the bad base fog in this thread: (there was a url link here which no longer exists)

 

[Ian Grant]

I doubt its worth it the fogging looks too bad. Start with a 1% solution of Potassium ferricyanide.

Then refix when ready.

Ian