I also read a trick somewhere that you can use a piece of clear acetate (over the print) for matching colors and densities by stippling on that first.
However, he discusses the use of it in this book 'The Print' and shares Edward Weston's recipe. I tried it, and it works. The gum arabic supports the adhesion of dye to print, and can be used to adjust and match the gloss level. If you can't get your hands on Spotone, and don't wont to use SpotAll (don't see why, by the way), it the way to go.