Diamond crystals grow in shapes (known as crystal habits) dictated by the arrangement of their carbon atoms in the cubic crystal system. These carbon atoms like to bond in the same way in every direction and this rigid structure makes diamond one of the hardest known natural materials. The most common crystal habit for diamonds is an octahedron form – like two square-based pyramids joined at their bases. Diamonds break more easily along the planes that follow this octahedron form; this type of break is known as cleavage and is different from a fracture, which can occur at any angle. Though we revere diamonds for their hardness, they are, in fact, less tough than some other gemstones as they break cleanly along this cleavage plane. Diamond cutters exploit diamond’s cleavage to cleave, or split, large crystals when they are cutting them. On a day-to-day basis, diamond’s perfect cleavage can also mean that if you hit your diamond along the direction of cleavage (which could happen for diamond-set engagement rings as we move our hands around so much), the stone may break. Luckily, diamond is very hard, so fractures are less likely, though still possible.

Diamonds set in rings are the most likely stones to get knocked, so remove rings for activities such as sports, gardening and DIY – this will also keep them cleaner.

Diamond is faceted to better show off its adamantine – the descriptor derived from the Greek for diamond that is applied to anything super hard and shiny – surface lustre and its fire (the flashes of spectral colours you see when you turn a diamond in your hands). The round brilliant cut is designed to make the most of diamond’s optical effects: the angles of the cut reflect light internally and from the external facet edges to give the shiniest of lustres and maximum brilliance (the sparkle we love diamond for), and they also split the light into the colours of the spectrum to create the fire. These facet edges are cut so precisely that they can be sharp.

Keep your diamond jewellery separate from the other jewels in your jewellery box so that the hard and sharp facet edges don’t scratch other stones and metal. Equally, if you have a pair of diamond earrings, wrap each separately, or place either side of a divider in your jewellery box so that they cannot scratch each other.

Diamond’s surface attracts grease, so you may feel you need to clean your diamond jewellery regularly, especially rings that are not removed when using soap, hand sanitiser and hand creams. Diamond is not porous, so using these everyday products will not damage your diamond, but they can affect other stones and metals, especially porous and organic gemstones, like pearls. For jewellery other than solely diamond-set platinum and gold jewels, it’s generally safer to remove these items before you use household cleaning products, make-up and perfume.

Antique diamond-set jewellery should be handled carefully as the settings may be delicate. Some antique jewels include gemstones in closed-back settings, where the metal wraps all the way round the back of the stone; if perfume or water or cleaning products get into the back of these settings, it may dry there as it cannot easily escape. For diamond jewels with closed-back settings, wipe them with a clean, soft cloth to remove any surface residue; do not soak them in water.

Diamonds in open-backed settings and secure jewels can be placed in an ultrasonic cleaner with hot water and solvent. Check that the settings and finer elements of your jewel are secure before using the ultrasonic because its vibrations may cause parts to break away. Do not include jewels set with heavily fractured diamonds as the vibrations may make the fractures crack further. Some fractures are filled with lead glass to make them less visible – but you should still be able to spot them if you look carefully – and ultrasonic cleaning can remove this glass filling.

Check our best-practice guide for ultrasonic cleaners.

If you do not own an ultrasonic cleaner, a simple and effective alternative is to leave your diamond-set jewellery in hot water for 10 minutes, then apply a dab of washing-up liquid to a soft toothbrush and gently brush to reach into and around the setting.

All transparent diamonds, whether colourless, yellow, pink, blue, brown or green, are very strong. Colourless diamonds are pure carbon, but the majority of diamonds contain trace amounts of other elements, which can alter a diamond’s colour. Coloured diamonds are increasingly popular, but they are exceptionally rare finds.

Larger clusters of other elements may be visible as crystal inclusions and can affect the durability of your diamond as most minerals are not as hard as diamond.

Black diamonds

Black diamond’s popularity is a relatively new phenomenon that has developed over the past 30 years. Small black diamonds are often used as striking accents in jewels and are becoming more popular as feature stones in their own right. Though they don’t have the fire and brilliance of transparent diamonds, opaque black diamonds have the dazzling lustre that diamond is renowned for.

The natural colours of black diamonds range from grey to brown, and greenish brown to black. They get their colour from their inclusions – clouds of minerals throughout the stone, including graphite, pyrite and hematite – or from cleavages and fractures that have become stained with other minerals or the process of graphitisation. This process is exploited to turn naturally grey diamonds into black diamonds by applying a high-temperature/low-pressure treatment to graphitise these grey diamonds’ fractures and turn them black.

The inclusions and their opaque nature make cutting and polishing the stones riskier because cutters cannot see internal fractures like they can in transparent diamonds. The inclusions may also make diamond’s characteristic crystal structure harder to interpret and so a cutter may have to break away from the standard shapes of diamond cuts.

The minerals of these inclusions may be more susceptible to damage than diamond’s carbon and so black diamonds must be handled with care. Their fractures make them more likely to break if knocked, so remove black-diamond-set rings before any physical activity. Black diamonds should be set carefully in jewels so that their facet edges are protected.

Do not put black diamonds in an ultrasonic cleaner; instead, clean them with a soft, clean cloth and use a soft toothbrush to reach around settings.

By getting to know our diamond-set jewels, it’s relatively simple to keep them at their sparkly best. As diamonds are often set with other gemstones, check out our guide to coloured stones care so that each element of your jewellery is in tip-top condition.