Why won't nickel plating brass in HCl (hydrochloric acid) work?

[PE9ZZ]

I got my lovely Pioneer SA-500A with two of the knobs having their shiny tops missing. Fortunately, this was already many years ago, I could get replacement tops on Feebay. However, they were brass and their color a pale yellow. Over time this darkened and it became ugly. So I decided I would nickel plate them.

I did a brief stint in chemistry so I embarked enthousiastically on this journey. All internet howtos I found used acetic acid (vinegar) as electrolyte. I decided to use hydrochloric acid instead because I am not a fan of organic acids. The priming of the solution using nickel coins (Dutch guilders) went great and produced a deep green clear solution. After I polished and cleaned the brass discs I hung one in the solution with a coin as anode and the brass disc as cathode. Nothing deposited. Only after I prepared a new solution with vinegar I got results. My chemistry is too rusty. I suspect the HCl is way too acid for the electrolysis to be successful but I fail to understand (read: am too lazy to investigate) why it fails.

Eventually I managed to produce acceptable results after I treated the polished brass discs with NaOH (sodium lye solution), again with electrolysis with the discs as kathode and (why not) a nickel coin as anode. Pro tip: use distilled water to clean a disc into the solution before going to the next step.

 

[IMF_Pioneer]

Electroplating isn't all as simple as some people try to make it out to be, that's why I did a 4 year apprenticeship to become a "1st. Class Electroplater". Generally you would pre plate using copper and then Nickel plate over the top. The issue with nickel is it also will dull off and oxidise, thus why Chromium is generally used over the top, making this a 3 stage process.

 

[HPMguy]

I was thinking of using an old computer PS to electro plate some razors to renew the nickel plating, but I was under the impression that sulfuric acid was the preferred electrolyte, using nickel sulfate.

It's all about the electrochemistry, and yes, it's really necessary to copper plate before nickel plating if you want shiny nickel instead of black.

 

[PE9ZZ]

I was thinking of using an old computer PS to electro plate some razors to renew the nickel plating, but I was under the impression that sulfuric acid was the preferred electrolyte, using nickel sulfate.

Won't work. Same reason as mine (acidity). And you will need an adjustable current. My objects are small disks and I eventually settled on 20 mA.

It's all about the electrochemistry, and yes, it's really necessary to copper plate before nickel plating if you want shiny nickel instead of black.

This is not true. In my case it was not needed, with other metals (steel?) it is. The lye treatment most definitely was. The black plating I got was just a too thin layer.

I found out the hard way (again) that chemistry is not easy. Nicely demonstrated in Breaking Bad... Also I didn't know that nickel salts are carcinogenous. Using gloves (nitrile) is mandatory. I though it wasn't but when I took them off there were lots of green spots all over them.