Problems in Gold plating

A. Hello Hayleigh. Some things that we understand about plating are based on crystal clear theory -- things that I like to call 'first principles'. Faraday's Law is the perfect example of this; it makes it absolutely clear & obvious that the plating thickness is directly proportional to the plating current times the plating time, and why. It lets you use simple arithmetic to answer all questions.

On the other hand there is empirical knowledge -- relationships that are based nearly totally on observation ('that's just the way things are') rather than a real scientific understanding. An example of that is the maximum satisfactory plating rate: although we appreciate general issues like boundary layer phenomena, adatoms, crystallization, temperature, ion migration, agitation, etc., we can't determine the maximum rate at which we can successfully plate by deep scientific calculation and understanding of these factors, but by knowing from past experience that exceeding a certain rate will result in burning rather than satisfactory plating, and having just a general acquired feel for the effects of those variables.

Solutions with low gold content are employed for reasons like: they don't 'immersion deposit' on the substrate, and they can be used as a 'garbage collection' step to trap impurities because they don't cost a fortune to replace. Appreciating this issue of empiricism, it can be hard to offer you a deep scientific explanation of why heavy gold plating from a low gold content solution tends to be a problem. It may be best to just accept that the type of deposit you will get from a low gold content solution (in terms of crystal size, porosity, hardness, etc.), just isn't highly compatible with thick plating.

Luck & Regards,

A. Hi Hayleigh
I had no problems plating 2 mm thick 80/20 gold/copper alloy on a regular basis.
BUT: I was not using 0.8 g/l. Probably 8.0 or more.
The value in the tank is eye watering at today's prices but you only use what you plate out. The problem with 0.8 g/l is that you rapidly deplete the gold in solution unless you are constantly replacing it - I assume that you do.
If your supplier says it cannot be done, I am guessing that you are buying from a jewelry supplier not a plating supply house. They buy in and sell on chemicals (with a mark up) but have very limited knowledge of the process.
Unless (unlikely) you are using a sulphite based solution, "acid" gold processes are based on GPC, Gold Potassium Cyanide but there is very little "free cyanide" in solution.
You might be interested in
https://www.academia.edu/10635761/Cyanides_in_Metal_Finishing_Risks_and_Alternatives
I cannot advertise but you can call the Institute of Materials Finishing for contact details of plating supply houses https://materials-finishing.org/

A. Sounds like the carbon treatment removed all or most of the gold brighteners. I'd do an analysis of the gold bath and determine brightener levels, or contact the bath manufacturer and advise him of the problem. I'm sure a simple replenishment of brightener will address the problem. .........BOB

A. From personal experience I have found activated carbon treatment to cause similar problems, a dull finish. We filter our baths to help eliminate contaminations but generally stay away from the activated carbon. Also we have found that even slight adjustments in PH will make a major difference in appearance. Try lowering your PH to 4.0 or 4.1.

We think the active carbon treatment which you have given to your gold bath is a bit heavy. You should give 0.5grams carbon per liter of gold solution, as your gold bath is cobalt hardened you need to replenish it with nickel standard solution so as to get the required shining, this nickel standard solution is easily available with your vendor, always keep the PH of the bath between 3.5 to 4, check it twice a day while work is going on.

Dear Chandrasekhar,
There is nothing strange, replenish your electrolytes with brightener and additives as specified by the supplier. Initially, please increase your bath density by increasing GPC concentration, and adding density correction salts.
Good Luck

A. Hi James. Although I doubt that nickel would leach through over a micron of precious metal plating, your company has moved forward to palladium in lieu of nickel, and I'd hate to see you go backwards. Nickel has been banned in jewelry in Europe and much of the world for a long time ... and one of these days concern for the public health will trump the blather & perks of lobbyists and it will be banned in the USA as well.

I don't know much about vacuum impregnation personally, but is a well known process for dealing with porosity. Hopefully someone more knowledgable in it will chime in to offer some details.

Luck & Regards,