Why is my gold turning black during plating?

[pete_1972]

Hi Folks,

I'm a total newbie who has just purchased a gold plating kit as a hobby

For my first experiment I did the old "copper coin connected to the cathode" test which resulted in a nice shiny golden coin.

However, I then left the coin in for a further 20-30 minutes only to find that, instead of the gold plating getting better, parts of the coin were now turning black.

I rubbed some polish over the coin and the cloth started turning black.

Did I somehow burn the gold? My voltage was a constant 6V.

Can't seem to find the answer anywhere, but I'm sure one of the guys on this forum will know :mrgreen:

Any ideas?

Thanks,

Pete

 

[goldsilverpro]

Hi Folks,

I'm a total newbie who has just purchased a gold plating kit as a hobby

For my first experiment I did the old "copper coin connected to the cathode" test which resulted in a nice shiny golden coin.

However, I then left the coin in for a further 20-30 minutes only to find that, instead of the gold plating getting better, parts of the coin were now turning black.

I rubbed some polish over the coin and the cloth started turning black.

Did I somehow burn the gold? My voltage was a constant 6V.

Can't seem to find the answer anywhere, but I'm sure one of the guys on this forum will know :mrgreen:

Any ideas?

Thanks,

Pete

Pete,

I'm not surprised at what happened.

What do the instructions say about plating time? Most of those gold plating solutions sold to hobbyists contain little gold and are therefore very sensitive to plating time. Most are limited to plating times of less than 1 minute (commonly, somewhere between 20-45 seconds, depending on the solution makeup). Otherwise, the plating will look good at first, but then, when left in the solution too long, it will start darkening and will become powdery, as yours has done. The longer you plate, the worse it gets. The black powder is essentially finely divided gold.

These hobbyist plating solutions and most jeweler's plating solutions are generally designed to only deposit "color" gold, i.e., just enough thickness, about 4-7 millionths of an inch, to "color" the object. Once the full gold "color" is achieved, the part should be removed from the solution.

I hope that you didn't remove too much of the gold that was in the solution by running it for such an extremely long time at 6V.

Read the manufacturer's operating instructions and follow them to the letter. It would be helpful if you could scan them and post them as an attachment. Or, if the instructions are on a website, post the link. I have considerable experience in gold plating and can most likely help you get off on the right foot. However, since there are several different types of solutions, I need to at least know what operating conditions (voltage, current density, temperature, time, agitation, etc.) are suggested by the manufacturer. It also might help me to know the concentration of gold in your solution, if that info is given in the instructions. This will usually be given in grams/liter. If that isn't available, tell me how much a specific amount of solution (100ml, 500ml, 1000ml, 1 pint, or whatever) costs. I can estimate the gold concentration by the price.

Chris

 

[Kiri]

One of the most likely reasons for the gold jewelry turning black is all due to the metallic abrasion, or low-quality plating as well as corrosion.

 

[Yggdrasil]

One of the most likely reasons for the gold jewelry turning black is all due to the metallic abrasion, or low-quality plating as well as corrosion.

Kiri.
Welcome to the forum.
The post you are commenting was made 11 years ago. And was sorted with a thorough answer.
Why comment on this?

 

[galenrog]

GSP was entirely correct. Why do you disagree? This is a common problem novices have when learning plating.

Time for more coffee.

 

[alicestevens]

I didn't know the answer on that, so happy I found this thread. Here is another good article I found on this matter Does Real Gold Turn Black When Burned?. Do you agree/disagree with it?

 

[butcher]

I find the article somewhat misleading but true, it does not give specifics on the oxidation of the gold.

I fail to see what that article has to do with electroplating gold and its problems.