altar

Topic: Gold plating rubs off in 15-20 seconds!

Hello all,
I had some silver medallions/tags cast for making engraved bracelets, and then had some of them rhodium plated and others gold plated (18k I was told).
I had read somewhere that the plating should be 3 microns thick to be lasting but I don't know of any way to measure the layer after the process. So I started rubbing one of the gold plated medallions with a silver cleaning cloth, and the plating came off in 15-20 seconds!
Is that normal? Obviously you shouldn't clean a plated medallion with that kind of cloth, but still... I did the same thing with a gold plated brass medallion I had bought and it didn't rub off.
1. How can obtain a better plating quality?
2. I know it depends mainly on 2 factors: the amount of gold in the bath, and the duration of the bath. What is the quantity and duration required to get a plating that is at least 1 micron thick?
3. Is there any way to test the quality of the plating?
4. I noticed some small marks on the plating and was told that it could be due to bubbles in the plating. Is there such a thing?
5. The are also some cloud-like marks on some of the pieces, any idea what could have caused that?
6. Will applying some kind of coating over the plating increase it's longevity?

I really hope someone will be able to help me,
Thanks a lot

jimtrottier

Re: Gold plating rubs off in 15-20 seconds!

Hi altar,

First is it rubbing off in flakes or is the silver rubbing through? if the silver is rubbing through your layer of gold is probably not heavy enough and if its coming off in flakes you have bad adhesion which would also explain the clouding due to bad cleaning. The bubbles you ask about do exist in the plating process on the parts during plating but with proper agitation and wetters in the bath they should not cause a problem. Thickness can be measured with x-ray witch is an expensive piece of equipment. Plating time can very from any given setup, in other words its something you have to play with until you get it locked in. I hope this helps

Jim

altar

Re: Gold plating rubs off in 15-20 seconds!

Thank you Jim for your answer,

The silver shows underneath, no flaking, so I suppose the layer just isn't thick enough.

You say that the clouding is due to bad cleaning, can they still be properly cleaned by the plater? (or do you mean the cleaning before the actual plating)

What is in your opinion a proper thickness for medallions that are in contact with the skin? Is 3 microns too thick? Too expensive?

Also, do you have any idea what kind of gold colored alloy I could have applied as underlayer so that the color difference is less obvious when the plating wears off?

Anyway I'm going to have to find another provider because the guy isn't going to change the way he works just because of me. I think they all do "flash coating" here, I don't know where I'm going to find what I want.


Thanks


Last edited by altar (01/02/2010 - 05:22 AM)

jimtrottier

Re: Gold plating rubs off in 15-20 seconds!

altar,

A decorative gold wash on jewelry is usually 2 to 4 mils, it might be that an under layer of nickel (although a little more alergenic than silver) would hold your color better. The clouding if you can't wipe it off was there before it went into the gold bath or the silver is leaching out.

Do you have a large quantity of these to plate? If not you could consider doing it yourself. ie:brush plating, there are a few companies out there that can supply you with what you need at a reasonable price. If you want I know of a few.

Jim 

Last edited by jimtrottier (01/02/2010 - 11:38 PM)

altar

Re: Gold plating rubs off in 15-20 seconds!

Thanks Jim,

If there are 25 microns in 1 mil, that's 50 to 100 microns for a gold wash? Surely you meant 2 to 4 microns didn't you?

I have about a hundred dollar or quarter sized flat round and heart shaped charms to plate. I expect to have that amount once or twice a month so I'm looking into non cyanide electroplating kits right now (hoping you can get the same quality than with cyanide solutions). If it's the only way to get a quality plating here in Korea (where I reside) I guess I'm just going to have to do it myself. I also thought I'd ask watch repair shops, because maybe durability of the plating is a bigger concern for them (I may be wrong).

Also, since some of these charms are meant to be worn by children, I need to find a nickel free underplate. Any suggestions about that? I read that for white gold you could plate a 5 micron layer of white bronze. But I wonder what I could use that's the same color as the gold I'll put over it?

Sebastian

Last edited by altar (01/03/2010 - 10:09 AM)

jimtrottier

Re: Gold plating rubs off in 15-20 seconds!

altar,

its 2-4 millionths of an in. I don't know about Korea but there are a few companies here in the states that sell kits not sure if they are non-cyanide I will take a look and get back to you

Try www.caswellplating.com

Jim

Last edited by jimtrottier (01/04/2010 - 02:55 AM)

gt214@att.net

Re: Gold plating rubs off in 15-20 seconds!

Altar, It looks to me like you have an adhesion problem, but, as some of the other folks have mentioned, you may just not be getting enough gold.

How many grams per liter of gold are in your bath?

Is this an Acid or an Alkaline gold solution (what color is the solution?) What temperature are you plating at?
What is the pH of the bath?

What kind of anodes are you using, how big are they,and what voltage are you using, and for how long are you plating?

Those questions will help resolve if you have a thickness issue.

Now, if you are having an adhesion problem:

You said you were plating with Rhodium on the same parts: is it ALSO rubbing off?

You are plating over Silver, which is tougher than plating over gold, it passivates and becomes electrochemically nuetral,and resists plating sometimes.....or it could just be still greasy or dirty from inadequate cleaning.

WET TEST your silver..if your parts come out of the last test looking dry or have "drops" of water on them instead of being uniformly coated with water, they are NOT ready to plate and need to be activated and/or cleaned again.

See my article "Solving Problems Plating Rhodium over Silver" can be found on Ganoksin, or email me for the article... glennt@davis-k.com, or see our website for it..www.davis-k.com. We make Rhodium, so we can advise on those kinds of issues. Good luck with your project.