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?
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.
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 Hg and it is type of mixture such that NaCl is soluble in water. When the gold and 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(Hg-356.7C and Au-2700C) Therefore when you heat the amalgam the Hg will boil and the gold will balance. But don't 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).
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.