How does a patina combination of copper sulphate and ammonium chloride solution react to copper 

I’ve a mokume gane ring of silver, rose gold and copper. To intensify the colour of copper I’ve been recommended to periodically wipe the ring with the above patina solution 

am keen to understand the impact of this on the copper over tome

thanks

Ammonium is slightly acidic and dissolves copperoxides from the ring. Ammonia is also complex agent for copper. Coppersulfate is catalyst. It should also work without copper sulfate, but slower.

23 hours ago, chenbeier said:

Ammonium is slightly acidic and dissolves copperoxides from the ring. Ammonia is also complex agent for copper. Coppersulfate is catalyst. It should also work without copper sulfate, but slower.

Thanks for this. It makes sense. But how does CuSO4 catalyse this process?  

Coppersulfate has already some solouble ions. Copperoxide dont have. So the process starts under and of solouble ions.