Antique jewellery is defined as being jewellery that is over 100 years old so it is not surprising that pieces can need a clean. Both the metal – gold, silver, platinum, etc – and the gemstones used may all show signs of dirt as well as wear. One of the first practical things we are taught in a gemmology diploma is how to clean gemstones. Polished and faceted gemstones, if touched by hands and fingers, can become smeary, which can make it difficult to see external and internal inclusions. Diamonds in particular are hydrophobic, that is, water repelling, but fats, oil, and grease can adhere to the surface, reducing the clarity. So, what were we taught to do? Take a squeeze of dishwashing liquid, add some just warm water and mix. Using tweezers, drop the stone into the water mix, agitate it a bit, then remove it and rinse in a dish of warm water. Then dry the stone on a lint free microfibre cloth. Very simple.
With antique jewellery, of course, we are dealing with gemstones that are in a setting so the gemstones can’t be removed. However, a simple cleansing of the piece in lightly soapy water and the use of a soft bristled toothbrush to clean the stones is usually all that is needed. But some antique jewellery pieces cannot be placed fully in water as this may damage the stones. For instance, if the piece has foiled gemstones, the water may seep into the back of the setting and oxidise the foil. Foiling of gemstones was a common practice in the 17th, 18th and first half of the 19th century, used to deepen the colour of the stones, to produce matched gemstones, and sometimes to impersonate a more expensive stone. Garnets in particular were still being foiled throughout the 19th century. If the settings are closed at the back, then the stones may have been foiled. It is best then to try to clean the stones with a soft slightly damp cloth and a soft brush.
Emeralds always need to be handled carefully because of the treatments they have traditionally received. Emeralds usually contain inclusions and because of this, most will have been treated in some way. Placing emeralds in oil to soak after mining so that internal fractures fill up was written about from the 14th century onwards. Soaking in warm soapy water can lead to some oil leaking out of the stone. Other stones, like jade, turquoise, amber, opals and coral, may also have undergone treatments such as filling, waxing and dyeing and should be handled cautiously. Again, as with foiled gems, try cleaning with a slightly damp cloth and use a soft brush. Be cautious. Strands of pearls should only be cleaned professionally.
There are commercially available jewellery cleaners available, mainly ultrasonic and steam, but, for the reasons mentioned above, they are usually not always appropriate to use for antique jewellery containing gemstones. Remember, the pieces of jewellery are old and need gentle treatment.