Al, do you remember the type of AF you used? If it was the commercially available kind, I've found it's much more acidic than needed, or desired, and has a tendency to darken over time despite what you might do to neutralize. If it was "home brewed", I'd suspect the same thing.
AF doesn't need to be highly acidic to work. A mix of one part nitric acid to six, or seven parts water, works well. Common household ammonia works well to neutralize.
Not sure if that was the problem here, but it's the first place I'd suspect.
Ed