Sometimes you may have seen an old gold ornament at home that has got spots or other signs of age. Your parents may take it to a ‘polisher’ to get it cleaned and polished. But did you know that the polisher actually removes a layer of gold?
You may have seen the video on aqua regia – the chemical that can dissolve gold. Gold is a ‘noble metal’. That means it will not react with anything ordinarily. It was so named because it can dissolve the so-called royal, or noble metals, although tantalum, iridium, and a few other metals are able to withstand it. But in jewellery it is actually alloyed with copper or silver, which tarnish over time.
Aqua regia (Latin for “royal water”) is a highly corrosive, fuming yellow or red solution. The chemical is very powerful and can dissolve gold within minutes. That’s because the nitric acid and the hydrochloric acid in it act together (They cannot dissolve gold by themselves). The nitric acid converts a tiny amount of gold metal to gold ions. These ions react immediately with the chloride ions from the hydrochloric acid. This causes even more gold atoms to turn into gold ions, and the reaction speeds up.
You should not clean gold ornaments with aqua regia. Aqua regia dissolves gold, even though neither constituent acid will do so alone, because, in combination, each acid performs a different task. Sadly, many people use it, claiming to be ‘gold cleaners’ or ‘gold polishers’. However, they are not being honest with you. They dip your gold ornaments for a little while in a solution of aqua regia, rinse them with water and give them back to you. The gold looks new and polished.
In truth, the aqua regia (the CAS number is 8007-56-5) has actually eaten up a few top layers of the gold. It is so thin that you won’t notice. But in a day’s work, ‘polishing’ hundreds of ornaments for unsuspecting people, a ‘polisher’ may remove quite a few grams of gold. He can then precipitate the gold using sodium bicarbonate.
To clean gold jewellery, all you really need is hot water, some soap and a toothbrush. That’s because most stains on gold jewellery are just dirt, which will go off with soap (But don’t do this if there are gemstones in the ornament, for soap water can leave stains on them). If they persist however, it is best that you take your ornaments to a professional jeweller for polishing.