"Water-break Free"

It is essential that parts be spotlessly clean before plating because for proper adhesion the plating must grow onto the raw metal of the substrate, which it cannot do if there is soil, oil, grease, or fingerprints on the surface.

The usual cleaning method prior to plating is alkaline cleaning, preferably a proprietary hot cleaner, followed by rinsing and another proprietary hot cleaner, this one with current applied to generate "scrubbing bubbles" of hydrogen or oxygen (although some substrates like aluminum cannot be electrified like that).

Simple qualitative evidence of cleanliness is a water-break free surface, meaning that when the parts are lifted from the cleaning tank, as the water sheds off the surface there are no "breaks"; rather, the entire surface stays wet.

Because the cleaning tanks are usually high in surfactants which discourage water breaks, it's best to look not just as the parts exit the cleaning tank but also as they exit the subsequent acid activation tank and its rinse.