Several years ago at the Montana Historical Gunmakers Guild Fair, we made stock stain by dissolving iron in nitric acid. I took some of that stain and some ferric nitrate (made from ferric nitrate crystals) and made some samples on the red maple from the rifle I was building at the time. At first the 2 stains were slightly different in color. Neither color was at all displeasing and certainly not any different than if they had been put on different pieces of wood. I put my samples on the shelf in my shop and forgot about them for a year or so. After a year I could not tell the difference between the color of the samples. Particularly after that experience I can see no reason to mess with dangerous acids and storage issues.
Just my 2c.
Bruce