Cyanide copper electrolytes are suitable for depositing copper over all ferrous and non ferrous alloys with the exception of aluminium and stainless steel both of which require special pre treatments.
Cyanide copper deposits are essential over zinc die cast parts and are extremely beneficial on soldered brass and copper work together with white metal castings and pewter.
Special features of cyanide copper solution are the excellent throwing power, probably better than any other solution, and a cleaning properties of the Rochelle on, being hot, cyanide based, and in the case of the strike solution, low efficiency so that plenty of hydrogen is produced to scrub and activate the surface.
Cyanide copper electrolytes go back to the very early days of electroplating and were probably developed from the silver cyanide electrolytes of Elkington and others.
There are two basic types of cyanide copper solution.
At the heart of cyanide copper electrolytes is copper cyanide which is insoluble in water and needs sodium or potassium cyanide in solution to aid the dissolution.
In a relatively low efficiency solution like strike cyanide copper with a typical efficiency of 20% a figure of 10 grams per litre of excess free sodium cyanide can reduce the plating rate to 0.
Cyanide copper is the type most commonly used in commercial plating, and the one with the widest field of application.
Cyanide copper solutions are typically high-throwing solutions based on copper cyanide dissolved in sodium or potassium cyanide.
A flash plating of cyanide copper is followed by a rinse and sulphuric acid dip before plating in acid copper until the required thickness is achieved.
, on the other hand, is more likely to suffer from the high alkalinity of the plating solution, and passivates based on sodium dichromate are very effective.