Q. What is the difference between immersion and electroless (autocatalytic) gold? Are the two processes interchangeable? R.M.
A. The immersion plating process is fairly simple. The substrate is placed in a solution containing a more noble metal, in this case gold. The surface layer of the substrate is displaced by the gold from the solution. You cannot get a very heavy deposit of gold using this process. Typically the deposit will only be a few atoms thick. Why? Once the surface of the substrate is coated with the gold, no more of the substrate surface can be dissolved. Immersion deposits typically do not adhere well to the substrate.
On the other hand, autocatalytic gold plating solutions contain reducing agents. When the substrate is placed in an autocatalytic plating solution and the part suitably catalyzed, the deposition of gold will continue until the part is removed from the solution or the solution is depleted of gold. The gold deposit is much thicker than that obtained from an immersion plating process, and it’s adherence to the substrate is much better.
Autocatalytic gold solutions are relatively new in the world of metal finishing. The granddaddy of these solutions is the electroless nickel plating solutions that are fairly well-known and understood.
The answer to your second question is no, the two processes typically cannot be interchanged. The immersion process is used mostly for decorative purposes while the autocatalytic process is used for specific high-tech applications. The immersion process has been around for many years and is used for plating jewelry findings, low-end gold colored items, etc.