Found this info on the steel wool posted by a chemist:
In my day , and maybe still, in Industry , it was called "Aging" the Bath-,??-of Chemicals.
It's purpose is to introduce Iron, which with use, would happen anyway. With low Iron levels, thin , patchy coatings would be evident. As the Iron content increased with use, the coatings would become denser and exhibit the sought after appearance. Doing it this way would produce a lot of scrap parts, but would increase the Iron levels (Titratable !) using KmNo4??Potassium Permanganate. Iron in solution is also an Oxidising agent, as is Sodium Nitrite (an accelerator) and as such the Titration method is the same.
Typically, again, in well formulated Compounds, there is no need to add steel wool, nuts and bolts etc to add Iron.
Immersion Class 1 phosphates can Run "on the Iron side"??Higher temp. or "on the Nitrite side", ZINC only. Nitrite keeps the Iron out of solution, allows faster coatiing times and smoother denser crystal formation, preferred for pre Paint applications.
To much iron will cause thin coarse coatings and eventually no coating if really high.
What you're doing in adding some old to new is Borderline brilliant !!? obviously the old will have Fe which can only help with a new mix.
