For example, an aluminum form or mandrel might be zinc immersion-coated. It may be the goal to grow a quarter inch of copper on this mandrel. If the zincated mandrel were directly immersed in the typical acid-copper bath directly, the zincate would dissolve before the copper could grow over it, and since direct copper plating of aluminum is unsatisfactory, the part could be ruined. The piece can then be plated additionally in another bath. We use cyanide copper baths with OFHC copper anodes circularly arranged, and elevate the temperature to 34.5 degrees Celsius.
Pieces go in electrically hot.
It should be noted that slight agitation should be used here, since generated hydrogen gas assists in forming a bright, quality copper plate. This bath contains cupric sulfate, sulfuric acid, perhaps formaldehyde, a tiny trace of chloride ion, and additional brighteners. In the bath used in the past, we added orthosphosphoric acid for deposit-smoothing properties over a broad spectrum of current densities. A proprietary bath is used, so it is hard to say what ALL the ingredients are. This bath uses phosphorized-copper anodes of about one square foot surface area.