Of all the problems that come to us, this is the one with the narrowest window and the least room for recovery.
What goes wrong
Copper and brass plating shows black or red spots. Sometimes within a day, sometimes over a week. The surface that came out of the tank bright and even develops marks that no amount of polishing will remove, because they are not on the surface, they are in it.
Bright metal is unforgiving. Skin oils from a bare hand are enough to start the reaction, and once oxidation has taken hold on a plated surface there is no cosmetic fix. The piece is either reworked from the plating stage or written off.
Two disciplines, both non-negotiable
Gloves, for everyone, at all times. Not just the plating operator. Anyone who moves, racks, inspects or packs a plated component. This is the part most units get wrong, because the plating operator is careful and the handler downstream is not.
Lacquer within eight hours. The protective clear goes on within eight hours of plating. Lacquer 60 is formulated as a clear for brass and copper specifically: it holds the shine and prevents tarnish on bright metals.
Eight hours is not a rounded guideline. It is the practical window before oxidation has progressed far enough to show through a clear coat.
Where dissimilar metals meet
A related problem worth knowing about: bi-metallic corrosion. Where two different metals are in contact, an electrochemical reaction takes place at the junction, and it is usually hidden inside the assembly where nobody sees it until the joint fails.
Corrosion Inhibitor CI1 coats nickel plating and prevents bi-metallic corrosion at those junctions. If you build assemblies that combine metals, this is worth designing into the process rather than adding after a failure.
And aluminium
Cast aluminium has its own requirements and its own coating. Lacquer AL is formulated for aluminium castings specifically.
The summary
Bright metal work is one of the few areas of finishing where the schedule matters as much as the product. Gloves on, lacquer within eight hours, and the problem simply does not occur.