# Why does mercury decolourise a gold ring?

I saw that a gold ring decolourised as it got in contact with mercury . Why does this happen ? Is there any way to reverse this?

• Jun 25 '17 at 8:11
• If the ring was "decolourised" by mercury (amalgamating with the gold) then 1) The ring is gold plated, and 2) No, there's no simple way to "put back" the gold on the ring. O:) Jun 25 '17 at 8:22
• Can't I use nitric acid? Won't it atleast remove the grey colour ? The ring is actually gold and not gold plated. Jun 25 '17 at 9:18
• @paracetamol I'm not sure why you think this is a sign the ring is gold-plated: mercury will damage any gold surface plated or not. Jun 26 '17 at 8:19
• @matt That the amalgam would stick to the surface of the ring slipped my mind >_<. Hence I thought "discoloration of ring" = "Part of the gold surface is lost" :P Jun 26 '17 at 16:43

The grey colour is an amalgam of mercury and gold.

Mercury forms amalgams with many other metals. Some are used as chemical reagents in laboratory chemistry as they have different properties than the original metals involved. Gold amalgam is much greyer than gold. Silver amalgam has been used in dentistry.

Mercury has been used in the extraction of gold in mining as it can extract gold from low grade ore. But the recovery process involves distilling off the mercury which is dangerous and polluting.

Chemists used to work with mercury a lot and, when they did, they were recommended to remove their wedding rings or other gold jewellery as the mercury would damage the gold.

Once the amalgam is formed there is no easy way to reverse the process short of resmelting the ring. If the contact with mercury has been brief, you might be able to polish it to remove the amalgam layer, but this won't be easy.

• Does immersing in acids or heating upto 350 degrees in help anyway?like mercury alone vaporises and gol remains intact. Jun 25 '17 at 10:05
• @Chit "Does immersing in acids or heating upto 350 degrees in help anyway?" Uh...are you sure you want your ring back in one piece? ;) Jun 25 '17 at 10:10
• As gold does not melt at that temperature, why can't this method be used. Would it make the ring brittle? Jun 25 '17 at 10:12
• If you're working with mercury, and your wedding ring is vulnerable, then you have a bigger problem than your wedding ring—you're working with mercury using your bare hands! Jun 25 '17 at 13:19
• I'm no expert in metallic toxicology, but I'm pretty sure the claim that you could drink liquid mercury "without much harm" is completely bogus. It is true that elemental liquid mercury is less toxic than other forms, and that vapor represents the largest risk, but that hardly means it is "safe". (Plus, the liquid form does vaporize at room temp.) I don't know if I'm just unusual, but it is rare that my hands are completely free of cuts, so even if absorption through intact skin is very slow, I'd say the typical lab worker is still putting herself at undue risk for not taking precautions. Jun 30 '17 at 9:47

Once when I was doing a experiment I have this experience, my ring was decolourised. I was afraid first but we can reverse it to the gold again.

There is no reaction between gold and $$\ce{Hg}$$ and it is type of mixture such that $$\ce{NaCl}$$ is soluble in water. When the gold and $$\ce{Hg}$$ mixed they make a amalgam, and this thing is call as amalgamation. It also uses to allocate pure gold by colluvies.

Before I said that there is no reaction between gold and mercury, therefore there is an easy way to allocate gold again. You know that boiling point of gold is more than mercury($$\ce{Hg}$$: $$\pu{356.7 ^\circ C}$$ and $$\ce{Au}$$: $$\pu{2700 ^\circ C}$$) Therefore when you heat the amalgam the $$\ce{Hg}$$ will boil and the gold will balance. But don't do this in the house, give it to a professional gold maker or a gold shop (After I experience this, I went to a gold shop and they heat my ring and it became such like before).

• Actually mercury was used for volume measurement using displacement principle. If it were done in a muffle furnace would it work (I don't have the idea of trying it out , asked just out of curiosity) Jun 25 '17 at 16:38
• did they just heat it to bring it back. After that was the layer smooth and still intact. Jun 25 '17 at 17:16
• It is a little inaccurate to describe amalgamation as the same as salvation: it is a little more complex than that. Jun 25 '17 at 19:41
• The boiling point of gold is irrelevant, here. If it //melts// your ring is lost already. Hopefully, 1064.18 °C for melting gold (wikipedia) is still far beyond the 356°C for boiling mercury. Not that it makes it a better idea to do at home. Jun 26 '17 at 12:59

The gold surface is simply "wet" by mercury and the gold is not decolorized. A tiny amount of mercury can quickly swarm across a gold surface making it appear that the color has changed almost instantly but the effect is superficial. When mercury was a common plaything, people would often coat silver coins with mercury. Mercury has the same effect on silver as it does on gold and the coins would become super shiny with a slick feel. After a few days, the mercury would either evaporate or oxidize leaving the coins badly tarnished. This is why it was common to find strangely dark looking silver coins in circulation. Mercury will leave the surface of a gold object in a few weeks, if not days, if left alone and the gold surface will return to normal. Heating the gold speeds the process but the gold is unharmed.

• Nope, mercury doesn't just coat the surface, it forms an amalgam and that process isn't easy to reverse. Jun 25 '17 at 19:42
• Thanks all for your active responses, actually the contact of the ring with mercury was very less. And it was just the top layer coated by amalgam . Jun 26 '17 at 11:23
• Because the ring is starting to get back its original color after three full days. Actually no attempt was made to remove the layer like heating or dipping in acid. But when I saw the ring after 3 days(the ring is not mine) the layer was gone mostly.And I beleive if I leave it for some more days it will naturally get back its own color and lustre(doubtful about lustre) Jun 26 '17 at 11:32

Mercury is a stable element . It has the ability to amalgamate most metals. Whenever the grey alloy is heated, based on their boiling point with mercury having the smaller, it will boil first leaving the precious metal, gold behind.