06 Jan Opal Care Guide
Opals are truly unique and mesmerising gemstones but they are sometimes considered fragile, or are they? How do they compare to other gems? Are there any special opal care requirements that you should be aware of? I will try to answers those questions, so that you can keep your treasures in pristine condition for years to come.
For us to discuss this topic, we must first understand different properties that relate to gemstone durability. How do they impact jewellery design, everyday usage and cleaning procedures. Some gems, pearls for example, are extremely sensitive- even mild acids, like vinegar can damage them. Others, like diamonds are a symbol of resilience when in fact one unlucky impact at wrong angle, can cause them to break apart. Jewellery designer must decide what gem is appropriate for which design and how to expose it, while protecting it at the same time.
Most people are familiar with gem’s hardness. Commonly defined in the gem world on the Mohs scale. It forms a non-linear order, where each stone can only be scratched by those above it. People sometimes mistake hardness for ability to withstand all sorts of mechanical damage. In truth, it’s an ability to resist surface scratching and nothing more. In this field diamond really does rule without a question. That’s why diamond powder is often used to cut and polish gems and in wide array of industrial applications. In fact, most of the diamonds mined and artificially produced are used for abrasive purposes. All gems will abrade with time but it’s important to protect softer stones when doing manual labour or playing sports.
Toughness is another property related to durability. It describes the resistance to breaking, as a result of impact. Usually greatest toughness is exhibited by polycrystalline materials, like a jade, where multitude of tiny crystals, oriented in various ways, create a strong, interlocking network that is uniformly resistant from every side. Toughness is thus separate from hardness. Some gems, like zircon, are hard but not tough at all. You can observe the effects of that on the edges that get chipped easily, while their facets remain unscratched .
Apart from normal fracture, which can occur in any material, there’s also a cleavage. It’s a special form of fracture, observed only in crystalline materials along certain planes. Similar to a grain in wood, certain stones can be easy to split in some directions while hard in others. It is caused by their atomic structure being easier to break along certain directions. This property was traditionally used to divide diamond crystals before cutting. Where a small incision was cut into diamond crystal’s side. Then, a chisel was placed there and was gently tapped with a hammer. Resulting in diamond crystal splitting along its plane of weakness. This method was used to save a lot of time on cutting diamonds and probably quite some material that would have to be ground into dust otherwise. Nowadays it is no longer used as we developed better and more reliable ways of splitting diamonds though.
Last category that relates to gem’s durability is stability. It’s an ability to resist chemical reactions that can be caused by acids, alkali, oxygen or energy. Stability varies from gem to gem, depending on their chemical composition. Most are fairly resistant but some can have a particular weakness. There are gems that shouldn’t actually be worn during the day, Conch pearls and kunzite both, can gradually fade in a sunlight.
Now, when we got the basics covered, let’s move on to the opal.
This gem is often described as a living stone because it contains water, which is present in it’s structure since the formation. During normal usage it’s not a problem. However, when storing it for extended periods of time in a dry environment, like a dessert or dehumidified safe storage. It’s a good practice to place your stone in a plastic bag with a bit of wet cotton or cloth. This precaution as far as I know is not needed for Welo opals- they can get completely dry without a worry. Australian opals however, have had a few cases where a stone was worn for decades without any issues. Until it was placed in a museum under hot halogens which, over extended period, caused it to dry out and develop cracks. In normal conditions, I have never had this kind of problem and I have been keeping many opals for years. In general, it is a good idea to buy opals from trusted source. So that you know it comes from stable deposit and has been seasoned after cutting.
Another thing you should mind, are sudden temperature changes. In general opal doesn’t mind being cold or hot as long as the temperature changes gradually, even so, I would personally protect it from extreme cold.
Opals from most commercial sources are quite stable and are not affected by household chemicals or detergents you may encounter in everyday life. Precaution connected specifically to Ethiopian Welo opals has to do with their porous internal structure. Opals from that locality have a sponge like structure, that allows for all sorts of liquids to be absorbed. While water may affect them for only a limited time, other liquids can cause permanent staining. Oils will cause them to loose play of colour, become transparent and get a yellowish tint. Drinks, such as tea or fruit juices, may change their body tone even if play of colour returns after drying. Should the worst happen, you can still try to remove foreign liquid by immersing your opal in acetone for some time. It is reportedly used at times, to speed up Welo’s drying process as well, but I’ve never tried it personally.
Opals are 5.5 to 6.5 on Moh’s scale of hardness and that puts them slightly below quartz which is 7. As a most abundant mineral on earth, quartz it’s also found in dust. This means you need to be careful while doing any manual labour and activites like gardening, sport and such. Especially if you have an opal ring or bracelet. As any jewellery worn on your hands is more prone to be damaged.
While cleaning your stones, use damp soft cloth. In case they are heavily soiled, the best way is to rinse them in warm water and dry with clean, soft cloth. Jewellers should avoid ultrasonic cleaners as they may cause cracking. Not all opals are prone to that, but you just never know unless it’s too late. Doublets and triplets of older origin, should be cleaned and used without soaking in water for too long. Modern glues used are 100% water resistant but you can never be sure with older stones.
Opals are quite tough but due to their non crystalline structure it is hard to foresee how resistant your gem really is, so the best way is to keep usual precautions and protect your stones from knocks. Previous GIA’s rapport show, Welo opals can actually withstand a fall on concrete floor from 1.5m without damage, but it obviously depends on size, shape and internal structure of the stone.
While storing, all jewellery pieces should be separate so that harder stones cannot scratch the softer ones. Advice especially important for softer stones like opals. Even if there are only harder gemstones present, they will scratch the gold, so the damage will be done in any case.
Due to their moderate hardness, opals are best suited to be used for necklaces, earrings, brooches. As those accessories are far less likely to sustain accidental damage than rings and bracelets. In case of Welo opals. There is less chance of wetting the stone that will hydrate it and drive the play of colour away for some time. Some Welos still have play of colour when hydrated, in others it comes back with the speed depending on atmospheric conditions. If you want to have an opal ring try to arrange some kind of protective design for it. The stone shouldn’t stick out too much, so the chance of hitting something with it is smaller. You may also use bezel setting to add extra level of protection.
I have to say opal does require more care than your average gemstone, but it is anything but. You can simply be sure, there’s no other stone exactly like yours!
Robert Zdeb 2013
Glenn Dizon’s designs at http://www.glenndizon.com/