John in NM
The ferric acetate solution was made using roughly a quart of vinegar and 1 biscuit of steel wool. After sitting 3 weeks or so, it was filtered with a coffee filter to remove any residual iron particles.

The order of all samples is the same in each photo, left to right:
1. 4 coats ferric acetate solution
2. 4 coats ferric acetate, followed by peroxide wash
3. 4 coats ferric acetate followed by lye wash, then peroxide -- this one looks most like the ferric nitrate stains I've seen.
4. 4 coats of ferric acetate mixed 50-50 with peroxide

All four samples finished with BLO thinned 25% with turpentine.

First two are in direct sunlight, the angle makes a big difference in the perceived color of the first and second samples:

This pic taken in shade, looks more like the eye perceives indoors:

Same shady location, but with the flash. This one is probably most accurate for colors, but you can't really see the grain in this moderately curly maple.

Now my chemistry is a bit sketchy, last class was 20 years or more back and I was really only paying much attention to the stuff I thought applied to mineralogy. So I won't attempt to explain how this works, I do understand the gist of it, but I'd have to fudge the details

We're sure to have a chemist lurking around here somewhere right?