Ferric acetate is also used for staining. It varies. I was testing some and had two batches. The gray looking batch gave redder results and the reddish looking batch gave gray results. Dissolve iron/steel into vinegar is how it's made. Unlike AF it does not require a heat blush. Great luck nailing the color you want. With enough testing you can find something, folks use everything, and I tested lots chasing the color for that first one. I think it's something folks spend less time fretting over as they make more guns, but I get trying to get "just so" for any particular one.
If you search on here you should find about 10,087 recipes and formulas and methods discussed. I've read most all of 'em.