The process

What this section covers

The four notes below take the deposition itself apart: the autocatalytic reduction that puts metal on the part, the role of each family of additives in the bath, the way a surface is made catalytic before it will accept anything at all, and the accident at the National Bureau of Standards in 1946 that turned a laboratory curiosity into an industrial process.

They also cover the practical consequence that decides most specifications: because no current flows through the bath, the deposit does not follow current density, so a blind hole, an internal thread or a re-entrant corner receives the same thickness as a flat face. That single property is why the process survives against cheaper alternatives, and it is why parts that cannot be plated any other way end up here.

How to read these notes

Every figure is followed by the condition that produced it, because almost nothing in this field is a constant: deposition rate depends on bath temperature, pH and loading; hardness depends on phosphorus content and on whether the part was baked afterwards. A number quoted without its condition is not usable on a drawing.

If you are specifying a coating for the first time, read the note on electroless versus electrolytic deposition first, then the note on the bath. If you are trying to understand why two suppliers quote different properties for what looks like the same finish, the answer is almost always phosphorus content, which is covered in the properties section.