Spray Chrome

The process the OP is asking about is two silver nitrate solutions that are reactive. When mixed they will react & deposit pure silver on the surface, more or less a plating. Silver will tarnish if not protected. This is why mirrors are painted on the back side, and why the process he is asking about needs a clear coat.

The DI water is part of the rinsing process, so that the pure silver is ready for clear coating. You can't mechanically clean the silver after deposition - it must be coated without touching it.

When re-silvering glass mirrors we would pour the solutions from two beakers at the same time in the center of the glass. It would plate out instantly with fresh solution. The runoff would plate things for a while, but was not something you could use the next day.

Commercial mirrors are still silvered the same way (chemically) with the previously mentioned dual head spray system. Sputtering or vacuum deposition is used to make first surface mirrors or reflective glass.

FYI, injection moulded plastics can certainly be chrome electroplated, just like a car bumper. A plastic part is rubbed down with finely powdered copper to make it conductive. Then it is copper / nickel / chrome just like it was steel.

B.