Ammonium chloride works well just by itself. You can probably find it in that book under the old common name of SalAmmoniac.
It was and to some still is a good soft solder flux.
You can buy it in a solid bar form about the size of a bar of soap at a welding type shop usually.
Just shave off some pieces (it's fairly soft) and let it disolve in plain (distilled) water which it does very easily.
Use that as the 'rusting solution'.
No worrys about copper or mercury. It was a primary slow rust brown soln for many years. Can be very aggressive in high humidity and temps. You have to experiment with the soln % but just about any amt will get you rusting,,just more and quicker as the concentration increases.
Wrap the remaining bar of sal ammoniac back up tightly and store in a plastic container or bag. The fumes from the stuff will rust steel objects that are around it in the shop.
Can't get much simpler than that.
