On 720 ABC Gillian O’Shaughnessy told us that she had a silver necklace that had hair entwined around it, and wanted to know if there was a chemical solution for removing it.
Yes and no. There is no chemical you can immerse it in that will dissolve the hair, leaving the silver behind. To dissolve hair you need hot nitric acid which falls into the “do not use this at home” category. Anyhow, it’d also dissolve the necklace…
A better solution is to burn the hair off with either a hairdryer or heat gun.
Gillian said she had tried this, but the silver had gone black.
Not to worry – it’s easy to restore, if you know a bit of chemistry. The black coating (or tarnish in general) is simply the metal oxide – in this case Ag2O. To remove it, we simply make a galvanic cell (battery) that reverses the oxidising process.
Place the necklace in an aluminium pie tray, add a generous amount of table salt and water and let it sit overnight. When you come back it’ll be shiny clean.
Several YouTube videos on this use baking soda and hot water to achieve the same effect. The baking soda is not necessary – all you need is a salt that will work as an electrolyte, and table salt (sodium chloride) is a better electrolyte than baking soda..
But the heat will speed the process, and may even assist the tarnish to flake off as the oxide coating is reduced right at the interface.
The chemistry of this is straightforward. Silvcer has a very positive standard reduction potential (about 0.8V) whereas aluminium has a very negative reduction potential (-1.66V). In layman’s terms, this means that when they are put together, the aluminium will reduce the silver and the silver will oxidise the aluminium, which is exactly what we want