Opal Care Guide
Opal care is an interesting subject. Opals are like all gemstones, they have special care requirements although usually their owners do not pay attention to this. Some gems, such as pearls are extremely sensitive- even mild acids like vinegar can damage them. Others, like diamonds, are a symbol of resilience when in fact one unlucky knock (at certain angles) can cause them to break.
Most people are familiar with the concept of hardness associated with gems, but they mistake it for the ability to withstand all sorts of mechanical damage when in fact hardness is defined as an ability to resist scratching and nothing more. In this field diamond really rules without question, that’s why only diamond powder can be used to cut and polish diamonds.
Toughness on the other hand is the resistance to breaking – toughness is best exhibited by polycrystalline materials such as jade. Stones like zircon are hard but not tough as demonstrated by the multiple chips often seen on facet edges yet lack of scratches on facet faces.
Aside from normal fracture, which can occur in any material, there is cleavage. A special form of fracture, cleavage is observed only in crystalline materials along certain planes; like a grain of wood, certain stones can be easy to split in some directions, hard in others. This property was traditionally used to divide diamond crystals before cutting, something which is rarely done nowadays as we have other, more efficient means.
The last category is stability, which is a gemstone’s ability to resist attack from acids, detergents and other chemicals, along with resistance to other environmental factors such as light, heat and radiation. There are some gems that shouldn’t actually be worn during the day, Conch pearls, kunzite and even amethyst, can gradually fade when exposed to sunlight.
Opal care sets some rules that it’s wise to follow in order to enjoy their beauty for a lifetime.
This gem is often described as a living stone because of its ability to absorb water, which is always present in its structure. During normal usage it doesn’t present a problem as opal will absorb moisture from your body but if you are storing opals for extended periods of time and live in a dry environment such as a desert region or use a safe storage, it is a good idea to place your stone in airtight plastic bag with a bit of wet cotton-wool or cloth. This precaution as far as I know is not needed for Welo opals- they can get completely dry without worry, but there have been cases where Australian opals that had been worn for decades with no issues have developed cracks having been placed in museums under hot halogens which, over extended period, caused it to dry out. Many opals do handle dry conditions well but best not to tempt fate! Trusting your suppliers is also important as opal should be seasoned after mining and after cutting to check if it’s stable to sell.
Opal care is more difficult than that of most other gems, another thing you should beware of are sudden temperature changes. In general opal doesn’t mind being hot or cold as long as the temperature changes gradually. However, I would personally protect it from freezing as water expands when frozen and you don’t want your opal to share the fate of a glass bottle forgotten for a night inside a freezer.
As opal has the ability to absorb liquids easily, you should keep it away from liquid chemicals as they may stain your stone. This is especially true for hydrophane Welo opal as their absorption ability is far greater than that of stones from other localities. Should the worst happen, you can try to remove the foreign liquid by immersing your opal in acetone for some time. Acetone is reportedly used at times to speed up Welo’s drying process as well but I’ve never tried it personally.
You should also bear in mind opal’s moderate hardness and toughness. Opals are a 5.5 to 6.5 on Moh’s scale of hardness and that puts them slightly below quartz which is a 7 and as a most abundant mineral on earth it’s a major component in dust. This means it is best not to wear opal jewellery, especially rings or bracelets, whilst doing any manual labour or activities such as gardening or sport.
Proper opal care is also applied to cleaning them when required. You wipe them gently with a clean, soft cloth or if they are heavily soiled, rinse them in warm water and dry with a clean, soft cloth. Jewellers should avoid all sorts of ultrasonic cleaners as they may cause cracking. Not all stones are prone to that, but you just never know unless it’s too late. Doublets and triplets, especially of older origin, should be cleaned without soaking in water for too long so the glue layer is not affected. Modern doublets and triplets don’t usually have this issue, as the glue that is used is not affected by the water.
Opals are moderately tough but due to their non crystalline structure it is hard to foresee how resistant your piece really is, so the best way is to take usual precautions and protect your stones from knocks. Previous reports from the GIA suggest that Welo opals can even withstand a fall on concrete floor from 1.5m without damage, but it obviously depends on the shape they are cut into and a particular piece’s internal structure.
Due to it’s moderate hardness, opal is best suited to use in necklaces, earrings, and brooches as these are far less exposed to damage than rings and bracelets, so this part of opal care falls mainly on jeweller and his sense of responsibility in advising you, what kind of jewel to make. In case of Ethiopian Welo opals, making accessories other than rings gives less chance of wetting the stone and thus hydrating it. That should be avoided as it usually drives the play of colour away for some time (many Welos still have play of colour when hydrated; in others it comes back with a speed dependent on atmospheric conditions).
Opal jewellery pieces should be stored separately so that harder stones cannot scratch softer ones. This is the general rule for all jewellery as even if there are only hard stones present, they will scratch both each other and settings, so damage will be done one way or another.If you really want to have an opal ring then a protective setting is desirable – for example, a bezel setting – as well as setting the stone as low as possible.
Summarising I have to say opals require more care than most gemstones, but you can be sure there’s no other stone like yours in the whole world!
Robert Zdeb 2013
Glenn Dizon’s designs at http://www.glenndizon.com/