Removing tarnish also removed the gold plating??

[SweetGold]

Hello all, thanks for a great forum!
Im pretty new to the world of refining and precious metals so please bear with me. Hopefully Im posting this in the right forum.

A friend of mine gave me these gold plated silver beads. She said she did the gold plating herself with 24K (she does jewelry, mostly as a hobby) and the beads were 999 silver (this I know to be a fact since I buy from the same source). It was some kind of left over stuff from her "playing around". The gold plating seemed only half way done and there was a lot of tarnish, mostly black and purplish stains. I guess it was kind of old. Pretty weird looking!

Soo, I figured I would use the "aluminum in the pot" tarnish removal method that I have done before with great success for "regularly" tarnished silver (--> http://scifun.chem.wisc.edu/homeexpts/tarnish.html) Only with a slight variation: Instead of baking soda I use plain salt. Well, after doing this I was kind of shocked to see that not only did all the discolorations go off but the gold plating too! :shock: I actually wanted to keep that!

Is this normal? Why would the gold move to the aluminum too? Maybe because the silver wasnt fully coated with it? You can clearly see a golden coloration on the aluminum foil now. How can I retrieve that?

Or is it possible that this wasnt even gold? Just some golden colored silver sulfide? Is there such a thing? Im really baffled and Im not sure if my friend has pulled a fast one on me. Or maybe a challenge (we do that between each other )...? Before I talk to her I would like to get some experts opinions...thanks a lot!

 

[element47]

I'll not call myself an expert, but if you truly dissolved or removed the layer of silver tarnish upon which gold plating was overlaid, what would the gold plating then have to stick to? In other words, don't you imagine you undermined the gold plating? You know you didn't use anything that can chemically dissolve gold.

 

[trashmaster]

I thing she is having FUN with you;;;; Go back to the link you posted and read the line second to the bottom...

 

[SweetGold]

I'll not call myself an expert, but if you truly dissolved or removed the layer of silver tarnish upon which gold plating was overlaid, what would the gold plating then have to stick to? In other words, don't you imagine you undermined the gold plating? You know you didn't use anything that can chemically dissolve gold.

I think you misunderstood what I was describing or maybe I described it poorly. The silver beads I was given were gold plated. ON the gold plating was the tarnish. Or rather, on the empty spots that werent covered with gold. Like I said, it was really odd looking. Im not sure if the tarnish was only where the gold plating was halfway done or not at all or if it was on fully plated areas too. Common sense would dictate the first.

But either way, that still wouldnt explain why any of the gold plating would move to the aluminum.? Or would it, seeing that it wasnt a full coating? Like I said, I still have the aluminum foil and you can see a slight gold stain on it. What method can I use now to see if this is gold or not, in other words recover it? LOL, burn the aluminum foil and collect the residue?

I thing she is having FUN with you;;;; Go back to the link you posted and read the line second to the bottom...

You mean this? "This type of reaction, which involves an electric current, is called an electrochemical reaction."
Ok...and? So?

Sure its an electrochemical reaction but Im wondering if this is actually an electrolysis? In other words, does the silver underneath the plating act as the anode and the aluminum serves as the cathode?

 

[Claudie]

I doubt that you have a recoverable, if any, amount of gold. You are saying that these beads were only partially plated if at all. How many pounds of them do you have?

 

[goldsilverpro]

If a migration barrier of plated nickel is not put between the silver and gold, silver can migrate through the gold and tarnish when it reaches the surface. At first, the plating will look good but sooner (with thin gold) or later (with thick gold), the tarnish will be visible. Typical jeweler's plating solutions are quite weak and the gold plated thickness is restricted to about 3 - 7 millionths of an inch thick - just thick enough so it has some color and you can't see through it. At 7 millionths, the gold covering one square inch of surface area would be worth only about 10 cents.

The method you used creates an electrolytic cell. In my opinion, due to gold being present, you should have used baking soda and not have used salt. I can see the possibility of enough chlorine being produced from the salt at the anode to dissolve the super-thin gold. Then, when the tarnish is removed and the reaction slows down, the gold in solution could easily immerse (cement) onto the aluminum. Makes sense to me.

 

[SweetGold]

I doubt that you have a recoverable, if any, amount of gold. You are saying that these beads were only partially plated if at all. How many pounds of them do you have?

I probably have a couple of ounces. My friend has a lot more though.

If a migration barrier of plated nickel is not put between the silver and gold, silver can migrate through the gold and tarnish when it reaches the surface.

No barrier! She said the gold was put straight on the silver. So thats interesting...how can it migrate through the gold? Will it automatically tarnish once it does so? Also, how come the tarnish takes on different colors? Most of the tarnish is black, but there is also some bluish and purplish coloration.

At first, the plating will look good but sooner (with thin gold) or later (with thick gold), the tarnish will be visible. Typical jeweler's plating solutions are quite weak and the gold plated thickness is restricted to about 3 - 7 millionths of an inch thick - just thick enough so it has some color and you can't see through it. At 7 millionths, the gold covering one square inch of surface area would be worth only about 10 cents.

Well, from the looks of it and the clues shes been giving me, the plating should be relatively thick. But no idea how thick. I dont think its standard jewelry thickness.

The method you used creates an electrolytic cell. In my opinion, due to gold being present, you should have used baking soda and not have used salt. I can see the possibility of enough chlorine being produced from the salt at the anode to dissolve the super-thin gold.

Im very happy to talk to such an expert, thank you! So why does chlorine have this ability? And I guess this confirms that the plating is rather thin? It went off almost in an instant as soon as I put the beads onto the aluminum foil (I had the salt well dissolved in the already boiling water). Do you think if I reduce the amount of salt I could avoid or reduce the effect of the gold being removed? Why would baking soda not have the effect of gold plating removal but still of tarnish removal? Sorry for all these questions but Im really curious and want to understand these things...

Then, when the tarnish is removed and the reaction slows down, the gold in solution could easily immerse (cement) onto the aluminum. Makes sense to me.

Ah, here we have the cementation again. So are you saying I found a cheap way of reverse electroplating!? :shock: The question still remains though - how do I recover the gold from the aluminum foil? Surely through another electrolytic process? Hmm, maybe one could just use an aluminum rod instead of aluminum foil. If I get some untarnished gold plated pieces would the beads still have to touch the aluminum? Because if not, I could just put the beads into a non metallic vessel with the baking soda solution and have an aluminum rod serve as the cathode. Do you think that could work?

 

[goldsilverpro]

No barrier! She said the gold was put straight on the silver. So thats interesting...how can it migrate through the gold? Will it automatically tarnish once it does so? Also, how come the tarnish takes on different colors? Most of the tarnish is black, but there is also some bluish and purplish coloration.

I really don't know the exact mechanism of why or how silver and/or copper migrates up through the gold (or, is it the other way around?) and, possibly, no one else does either. I just know it happens. There's quite a bit of info about this on the internet. Also, I have seen it occur many times. An old jewelry product is vermeil, which is still made. This is sterling silver plated with about 3 microns (120 millionths) of gold. It is normally made without a nickel (or, palladium) barrier. With no barrier, even at this gold thickness, silver will eventually migrate to the surface and the vermeil will tarnish. If you search the internet, you'll find lots of references to this and how to clean tarnished vermeil objects without damaging the gold. Besides gold thickness, the rate of migration to the surface depends on several things such as the storage temperature of the plated object or the gold crystal structure, internal stress, and amount of porosity produced by the specific bath chemistry and/or the amount of current that was applied during the gold deposition.

Well, from the looks of it and the clues shes been giving me, the plating should be relatively thick. But no idea how thick. I dont think its standard jewelry thickness.

In general, thin gold looks just like thick gold, but the other clues I'm getting would indicate thin gold. To get an idea of how thick she plated the beads, I would definitely ask her how long the beads spent in the gold plating solution. If she only plated for 15-60 seconds, the plating is quite thin. If she plated for 15-20 minutes, it could be quite thick. Most all of the gold plating solutions that are sold by companies providing jewelry making supplies only contain about 1 to 2 g/l of gold. These are limited to thin deposits only. Depending on the exact plating bath makeup, after plating for 30 seconds, or so, the gold deposit will start visually darkening or changing in some other way and the gold appearance will not be acceptable. If she plated thick gold, she would have required a solution with a lot more gold in it and these could cost about $500/liter or more. You might also ask her how much (and when?) she paid for a specific amount (say, 1 liter) of solution.

Ah, here we have the cementation again. So are you saying I found a cheap way of reverse electroplating!? :shock: The question still remains though - how do I recover the gold from the aluminum foil? Surely through another electrolytic process? Hmm, maybe one could just use an aluminum rod instead of aluminum foil. If I get some untarnished gold plated pieces would the beads still have to touch the aluminum? Because if not, I could just put the beads into a non metallic vessel with the baking soda solution and have an aluminum rod serve as the cathode. Do you think that could work?

Bad idea. Whether using foil or a rod, separating the gold from the aluminum would not be a pleasant, safe, or easy task. I can think of no method that would not involve dissolving all of the aluminum away from the gold. Offhand, this would take something nasty like sodium hydroxide or hydrochloric acid. Most knowledgeable gold refiners avoid aluminum like the plague.

 

[Harold_V]

I really don't know the exact mechanism of why or how silver and/or copper migrates up through the gold (or, is it the other way around?)

I don't recall the particulars, but Rose discusses the migration of metals in his book, The Metallurgy of Gold. It has been known for at least 100 years. Ingots of gold and silver that are in intimate contact experience this phenomenon---the items need not be plated.

Harold

 

[Harold_V]

:shock: The question still remains though - how do I recover the gold from the aluminum foil?

One can use sodium hydroxide or HCl to dissolve the aluminum, saving all solid residues for eventual processing for the recovery of gold. By allowing gravity to settle the solids, then siphoning, you can rinse the material enough times to eliminate aluminum in solution.

As Chris said, wise refiners avoid aluminum much the same was as wise refiners avoid tin---but you can deal with both if you have patience.

Harold

 

[Barren Realms 007]

I really don't know the exact mechanism of why or how silver and/or copper migrates up through the gold (or, is it the other way around?)

I don't recall the particulars, but Rose discusses the migration of metals in his book, The Metallurgy of Gold. It has been known for at least 100 years. Ingots of gold and silver that are in intimate contact experience this phenomenon---the items need not be plated.

Harold

It could be a form of electrolysis that set's up between 2 different types metals.

 

[Harold_V]

Here's where we need Lou's education.

I'm inclined to think it's more to do with covalent bonding. The two metals are likely sharing electrons, but not in the sense of an electrical flow. Don't know that that even makes sense. :lol:
To imply electrolysis suggests an electrolyte. None is required. Just intimate contact.

Harold

 

[SweetGold]

I really don't know the exact mechanism of why or how silver and/or copper migrates up through the gold (or, is it the other way around?) and, possibly, no one else does either. I just know it happens. There's quite a bit of info about this on the internet. Also, I have seen it occur many times. An old jewelry product is vermeil, which is still made. This is sterling silver plated with about 3 microns (120 millionths) of gold. It is normally made without a nickel (or, palladium) barrier. With no barrier, even at this gold thickness, silver will eventually migrate to the surface and the vermeil will tarnish. If you search the internet, you'll find lots of references to this and how to clean tarnished vermeil objects without damaging the gold. Besides gold thickness, the rate of migration to the surface depends on several things such as the storage temperature of the plated object or the gold crystal structure, internal stress, and amount of porosity produced by the specific bath chemistry and/or the amount of current that was applied during the gold deposition.

That's really fascinating. I did read about vermeil not too long ago but about the detailed mechanisms why it tarnishes. I will look deeper into this. You mentioned temperature - I take it that the warmer the conditions are the stronger the migration/tarnishing occurs?

In general, thin gold looks just like thick gold, but the other clues I'm getting would indicate thin gold. To get an idea of how thick she plated the beads, I would definitely ask her how long the beads spent in the gold plating solution. If she only plated for 15-60 seconds, the plating is quite thin. If she plated for 15-20 minutes, it could be quite thick. Most all of the gold plating solutions that are sold by companies providing jewelry making supplies only contain about 1 to 2 g/l of gold. These are limited to thin deposits only. Depending on the exact plating bath makeup, after plating for 30 seconds, or so, the gold deposit will start visually darkening or changing in some other way and the gold appearance will not be acceptable. If she plated thick gold, she would have required a solution with a lot more gold in it and these could cost about $500/liter or more. You might also ask her how much (and when?) she paid for a specific amount (say, 1 liter) of solution.

I too think that its rather thin plating. But to be honest, Im not sure that it was actually done in a bath. I mean to say that she probably brushed it on manually...which of course still requires a gold solution. The reason I suspect brushing is because of the unevenness and incompleteness of the plating. Which is probably another factor for the tarnishing.

Bad idea. Whether using foil or a rod, separating the gold from the aluminum would not be a pleasant, safe, or easy task. I can think of no method that would not involve dissolving all of the aluminum away from the gold. Offhand, this would take something nasty like sodium hydroxide or hydrochloric acid. Most knowledgeable gold refiners avoid aluminum like the plague.

Yeah, Ive gathered this by now too. Oh well, its still a cool way of removing tarnish in general. 8)

I don't recall the particulars, but Rose discusses the migration of metals in his book, The Metallurgy of Gold. It has been known for at least 100 years. Ingots of gold and silver that are in intimate contact experience this phenomenon---the items need not be plated.

Hmm, one could almost say gold and silver have an affinity for each other. Especially if the attraction/migration goes both ways...? Funny, seeing that often gold is associated with males and silver with females...

One can use sodium hydroxide or HCl to dissolve the aluminum, saving all solid residues for eventual processing for the recovery of gold. By allowing gravity to settle the solids, then siphoning, you can rinse the material enough times to eliminate aluminum in solution.

Would this produce any toxic fumes?

Here's where we need Lou's education.
I'm inclined to think it's more to do with covalent bonding. The two metals are likely sharing electrons, but not in the sense of an electrical flow. Don't know that that even makes sense. :lol: To imply electrolysis suggests an electrolyte. None is required. Just intimate contact.

Ok, this leads me to another question Ive been wondering about for some time. Is there negatively charged gold as well as positively charged gold? Which occurs more naturally? Does this question even make sense? :lol:

 

[goldsilverpro]

I too think that its rather thin plating. But to be honest, Im not sure that it was actually done in a bath. I mean to say that she probably brushed it on manually...which of course still requires a gold solution. The reason I suspect brushing is because of the unevenness and incompleteness of the plating. Which is probably another factor for the tarnishing.

It sounds like the tarnish was uneven rather than the plating surface. On most stuff I've seen, it's been uneven. This may be partially due to the variation of plating thickness of the part. In general, the high points and the edges will be thicker than the center or depressed areas - it can be as much as 3 times thicker.

I guess she could have used gold paint, but I know of no true gold paint available (that doesn't mean it isn't). About the only other real gold coating option besides plating is "liquid gold", which is used on ceramics and glassware. This has to be fired, though, to bring out the brilliance, drive off the solvent, and make it stick to the object. Maybe that's what she used and the firing heat immediately migrated the silver to the surface.

 

[Harold_V]

Ok, this leads me to another question Ive been wondering about for some time. Is there negatively charged gold as well as positively charged gold? Which occurs more naturally? Does this question even make sense? :lol:

<<<<<<<<sigh>>>>>>>
With my history of no education, and that I struggled to get out of high school, you ask me? :lol:

Harold