Understanding Gemstone Hardness
Before you clean or handle any gemstone, it is essential to understand the concept of hardness and why it matters so much for care. The Mohs scale of mineral hardness, devised in 1812 by the German mineralogist Friedrich Mohs, ranks minerals from 1 (talc, the softest) to 10 (diamond, the hardest). This scale tells you which stones can scratch which, and therefore which stones need the most careful handling.
The Mohs Scale for Common Gemstones
Here are the hardness ratings for the gemstones you are most likely to own:
- 10, Diamond: The hardest natural substance. Can only be scratched by another diamond.
- 9, Ruby and Sapphire (corundum): Extremely hard and durable. Excellent for everyday wear.
- 8, Topaz: Hard and scratch-resistant, though it can chip along cleavage planes if struck sharply.
- 7.5, Emerald (beryl): Moderately hard, but emeralds often contain internal fractures (known as "jardin") that make them more vulnerable to damage than their hardness rating suggests.
- 7, Quartz (amethyst, citrine, rose quartz): Durable enough for most jewellery but can be scratched by harder stones.
- 6.5-7, Garnet, Peridot, Tourmaline: Reasonably hard but benefit from careful handling.
- 6-6.5, Opal, Tanzanite: Soft enough to scratch relatively easily. Require extra care.
- 5-6, Turquoise, Lapis Lazuli: Porous stones that can absorb liquids and chemicals.
- 2.5-4.5, Pearl, Coral, Amber, Jet: Organic gems that are very soft and require the gentlest care.
Why Hardness Matters for Care
The practical implication of the Mohs scale is simple: a stone can be scratched by anything with a higher hardness rating. This means:
- Diamonds can scratch every other gemstone (and other diamonds)
- Rubies and sapphires can scratch everything except diamonds
- Quartz dust (hardness 7), which is present in ordinary household dust, can scratch any stone rated below 7
This is why storing gemstones separately is so important. A diamond ring tossed casually into a jewellery box alongside opals, pearls, and emeralds could scratch every other stone it touches.
It also explains why some gemstones are better suited to everyday wear than others. Diamonds, rubies, and sapphires can withstand the knocks and abrasions of daily life. Emeralds, opals, and pearls are better reserved for occasional wear and should be treated with greater care. Understanding hardness is also important when it comes to valuation — our coloured gemstone valuation guide explains how durability, alongside colour and clarity, affects what your stones are worth.
Cleaning Your Diamonds
Diamonds may be the hardest gemstone, but they attract grease and oils readily, which dulls their sparkle. Regular cleaning keeps diamonds looking their brilliant best.
The Warm Soapy Water Method
The safest and most effective method for cleaning diamonds at home is also the simplest:
- Fill a small bowl with warm (not hot) water and add a few drops of mild washing-up liquid
- Place your diamond jewellery in the bowl and leave it to soak for 20-30 minutes
- Gently brush each piece with a soft toothbrush, paying particular attention to the underside of the stone and the areas around the prongs where dirt accumulates
- Rinse thoroughly under warm running water (place a sieve over the drain as a precaution)
- Pat dry with a soft, lint-free cloth
This method is safe for diamonds set in gold, platinum, and silver. It is also safe for diamonds set alongside rubies and sapphires, which share diamonds' tolerance for warm soapy water.
Ultrasonic Cleaners
Ultrasonic cleaners use high-frequency sound waves to create microscopic bubbles that dislodge dirt from jewellery surfaces. They are highly effective for diamonds and can reach areas that a toothbrush cannot. However, ultrasonic cleaning is not suitable for all gemstones (more on this below) and should be used with caution even for diamonds.
Avoid ultrasonic cleaning if your diamond:
- Has been treated with fracture filling (the vibrations can damage the filler)
- Is set in a piece with other, softer gemstones
- Has a loose setting (the vibrations could dislodge the stone)
Steam Cleaning
Professional jewellers often use steam cleaners to finish cleaning diamonds. The combination of heat and pressure removes residual dirt and restores maximum sparkle. Home steam cleaning machines are available, but exercise caution. The high temperature and pressure can damage other gemstones, loosen settings, and cause thermal shock in stones with inclusions.
What to Avoid
- Bleach, chlorine, and harsh chemicals: these can damage the metal settings and, over time, weaken the prongs holding your diamond in place
- Abrasive cleaners or cloths: while they will not scratch the diamond itself, they can damage the metal setting
- Toothpaste: despite the popular myth, toothpaste is too abrasive for jewellery cleaning and can scratch softer metals
Caring for Coloured Gemstones
Coloured gemstones each have their own care requirements. What works for a sapphire could damage an emerald, so it is important to know what you are working with.
Ruby and Sapphire
Rubies and sapphires (both varieties of corundum, hardness 9) are among the most durable gemstones and can tolerate the same cleaning methods as diamonds. Warm soapy water is ideal. Ultrasonic cleaning is generally safe unless the stone has been fracture-filled or cavity-filled, or unless it contains unusually large inclusions.
Heat-treated rubies and sapphires (the vast majority on the market) are stable and do not require any special handling beyond what you would apply to an untreated stone.
Emerald
Emeralds require significantly more care than rubies and sapphires. Nearly all natural emeralds contain inclusions and internal fractures, and it is standard practice to treat emeralds with oil or resin to improve their clarity. This treatment is accepted in the trade but has important implications for care:
- Never use ultrasonic cleaners on emeralds, as the vibrations can extend existing fractures and strip away oil treatments
- Never use steam cleaners, as the heat can cause the oil to sweat out of the stone, making inclusions more visible
- Avoid sudden temperature changes; thermal shock can crack an emerald
- Clean only with warm soapy water and a very soft cloth. Do not soak for extended periods
If your emerald appears to have become cloudier or less vibrant over time, it may need re-oiling by a professional gemologist.
Tanzanite
Tanzanite (hardness 6.5) is a beautiful but relatively delicate stone. It is sensitive to sudden temperature changes and can cleave (split along crystal planes) if knocked sharply. Clean with warm soapy water only. Avoid ultrasonic and steam cleaning entirely. Tanzanite is best suited to earrings, pendants, and occasional-wear rings rather than everyday rings.
Opal
Opals (hardness 5.5-6.5) contain water within their structure, and this makes them vulnerable to dehydration and cracking, particularly in dry, heated environments. Care for opals includes:
- Store in a slightly humid environment (some collectors keep a damp cotton wool ball in the storage box)
- Clean only with a damp soft cloth. Never immerse in water for prolonged periods
- Avoid all chemicals, ultrasonic cleaning, and steam
- Protect from sudden temperature changes and direct sunlight
- Be especially careful with doublets and triplets (layered opal constructions), which can delaminate if exposed to water
Topaz and Aquamarine
Topaz (hardness 8) and aquamarine (hardness 7.5-8) are reasonably durable but have a tendency to chip along cleavage planes if struck sharply. Clean with warm soapy water. Ultrasonic cleaning is generally safe for untreated stones, but avoid it for irradiated topaz (the colour can fade with heat exposure).
Caring for Organic Gems
Organic gems, those formed by biological processes rather than geological ones, are among the most delicate materials used in jewellery. They require a fundamentally different approach to care.
Pearls
Pearls (hardness 2.5-4.5) are composed of nacre (calcium carbonate) layered by molluscs. They are soft, porous, and sensitive to acids, chemicals, and heat. Essential pearl care includes:
- Wipe after every wear with a soft, damp cloth to remove perspiration, perfume, and body oils
- Apply cosmetics before putting on pearls. The "last on, first off" rule. Perfume, hairspray, and cosmetics contain chemicals that can dissolve nacre over time
- Never clean with chemicals, vinegar, or acidic solutions, as these will dissolve the nacre
- Store separately in a soft cloth pouch, away from harder gems that could scratch them
- Wear your pearls regularly. Nacre benefits from the slight moisture of skin contact. Pearls stored unworn for decades can dry out and crack
- Have pearl strands restrung periodically (every one to two years for frequently worn strands), as the silk thread stretches and weakens over time
Amber
Amber (hardness 2-2.5) is fossilised tree resin, warm to the touch and remarkably light for its size. It is soft, can be scratched easily, and dissolves in alcohol and some solvents. Clean amber only with a soft, dry cloth. If necessary, use a barely damp cloth, but never immerse amber in water or expose it to cleaning solutions. Store away from direct sunlight, which can cause amber to darken and become brittle over time.
Coral
Coral (hardness 3-4) is the calcified skeleton of marine organisms. Like pearls, it is sensitive to acids and chemicals. Clean with a dry or barely damp soft cloth. Avoid all immersion in water, cleaning solutions, and ultrasonic or steam cleaning. Red and pink coral are the most valuable varieties and should be handled with particular care.
Jet
Jet (hardness 2.5-4) is fossilised wood, famously associated with Whitby in North Yorkshire and widely used in Victorian mourning jewellery. It is lightweight, warm to the touch, and can take a high polish. Clean with a soft, dry cloth. Jet is sensitive to heat and can crack if exposed to extreme temperatures. Avoid chemical cleaners and prolonged exposure to sunlight.
Storage and Handling
Proper storage is one of the simplest and most effective ways to protect your gemstone jewellery.
Individual Pouches and Compartments
Every piece of gemstone jewellery should be stored separately, ideally in its own soft cloth pouch or in a lined jewellery box with individual compartments. This prevents harder stones from scratching softer ones and stops chains from tangling.
For particularly valuable pieces, consider acid-free tissue paper wrapping inside the pouch for additional protection.
Temperature and Humidity
Most gemstones prefer stable, moderate conditions. Avoid storing jewellery near radiators, in direct sunlight, or in bathrooms where temperature and humidity fluctuate dramatically. A bedroom drawer or wardrobe shelf is usually ideal.
Opals and pearls benefit from slightly higher humidity. If your home is particularly dry (common with central heating), consider keeping these gems in a lightly sealed container with a small piece of damp cotton wool nearby.
Chemicals and Perfume
Always remove gemstone jewellery before:
- Applying perfume, hairspray, or cosmetics
- Using household cleaning products
- Swimming in chlorinated pools or the sea
- Gardening or doing manual work
- Applying hand cream or sunscreen
Even seemingly harmless substances can, over time, build up on gem surfaces, react with treatments, or corrode metal settings.
When to See a Professional
Regular professional inspection can prevent small problems from becoming expensive ones.
Loose Stones
If you notice a gemstone in your jewellery moving, clicking, or sitting at an angle, stop wearing the piece immediately and take it to a professional jeweller for prong tightening or re-setting. A loose stone is at risk of falling out and being lost, which is a far more costly outcome than a simple repair.
Worn Prongs
Over time, the metal prongs that hold gemstones in place wear down through everyday contact. A professional can assess prong wear and re-tip or rebuild prongs before they fail. An annual check-up is recommended for rings and bracelets (which receive the most wear), and every two to three years for necklaces, earrings, and brooches.
Clouding and Surface Damage
If a gemstone appears cloudier or less vibrant than it once did, it may have surface scratches, accumulated grime beneath the setting, or degraded treatment (such as oil drying out of an emerald). A professional can diagnose the issue and recommend appropriate restoration, whether that is repolishing, re-oiling, or simply a thorough professional clean.
Annual Checks
Consider having your most valuable and frequently worn pieces professionally inspected once a year. This is particularly important for engagement rings and other daily-wear items. A professional will check settings, prongs, clasps, and the overall integrity of the piece, catching potential issues before they result in stone loss or structural failure.
Common Mistakes That Damage Gemstones
Even well-intentioned owners can inadvertently damage their gemstones. Here are the most common mistakes to avoid.
Using Household Chemicals While Wearing Jewellery
Bleach, ammonia, and chlorine-based cleaning products can corrode gold alloys, dissolve organic gems, and damage gemstone treatments. Always remove jewellery before cleaning your home. This single habit will prevent more damage than any amount of careful cleaning.
Ultrasonic Cleaning the Wrong Stones
Ultrasonic cleaners are excellent for diamonds, rubies, and sapphires, but they can shatter emeralds, opals, tanzanites, and pearls. Never place a piece in an ultrasonic cleaner without first confirming that every stone in the piece can tolerate it. A ring with a diamond centre stone and emerald side stones should not go in the ultrasonic, because the emeralds cannot withstand it.
Wearing Rings During Manual Work
Gardening, DIY, gym work, and even vigorous cooking can expose rings to impacts, chemicals, and abrasion. Rings are particularly vulnerable because they protrude from the hand and come into contact with everything you touch. Get into the habit of removing your rings before any physical activity.
Storing Everything Together
Tossing all your jewellery into a single box or drawer is a recipe for scratches, tangles, and damage. Diamonds will scratch everything else, metal clasps will catch on delicate chains, and soft stones like opals and pearls will be damaged by harder neighbours. Invest in proper storage; it is inexpensive and prevents costly damage.
Ignoring Damage
A small chip, a slightly loose stone, or a worn prong may seem minor, but these issues invariably worsen with continued wear. Address problems promptly. A five-minute repair by a professional jeweller is far cheaper than replacing a lost stone.
Understanding Gemstone Treatments
The vast majority of coloured gemstones on the market have been treated in some way to enhance their colour or clarity. Understanding these treatments is important both for care and for valuation.
Heat Treatment
Heat treatment is the most common gemstone enhancement. Rubies, sapphires, tanzanites, and many other stones are routinely heated to high temperatures to improve colour and reduce inclusions. This treatment is permanent, stable, and widely accepted in the trade. Heat-treated stones do not require any special care beyond normal best practice.
However, heat treatment does affect value. An untreated ruby or sapphire of comparable quality will be worth significantly more than a treated stone, sometimes several times more.
Fracture Filling
Fracture filling involves injecting glass, resin, or oil into surface-reaching cracks to improve a stone's appearance. This treatment is common in emeralds (oil filling) and rubies (glass filling). Filled stones require extra care:
- Avoid ultrasonic and steam cleaning
- Avoid exposure to heat and harsh chemicals
- Be aware that fillings can degrade over time and may need re-application
Glass-filled rubies are particularly important to identify, as the glass content can be substantial and significantly affects both durability and value. A professional gemologist can identify glass filling under magnification.
Surface Coating
Some gemstones are coated with a thin film to enhance colour or add optical effects (such as the "mystic" coatings applied to topaz). Coated stones should be handled very gently. The coating can wear off, scratch, or peel, particularly with exposure to chemicals or abrasion. Clean coated stones only with a soft, dry cloth.
Irradiation
Irradiation is used to create or enhance colour in stones such as blue topaz, fancy-colour diamonds, and some tourmalines. The treatment is typically stable and permanent, though some irradiated colours can fade with prolonged exposure to heat or intense light. Irradiated stones do not pose any health risk and can be cared for normally, but avoid leaving them in direct sunlight for extended periods.
Diffusion Treatment
Diffusion treatment involves heating a stone in the presence of certain elements (such as titanium or beryllium) that diffuse into the crystal structure and alter its colour. Surface diffusion affects only a thin layer and can be removed if the stone is recut or chipped. Lattice diffusion penetrates deeper and is more stable. Diffusion-treated stones should be identified at the time of purchase, as the treatment significantly affects value.
Is Your Gemstone Valuable?
If you own gemstone jewellery and are curious about its value, here are the key factors that professionals consider.
The Four Cs for Diamonds
Diamond valuation is based on four criteria, universally known as the four Cs:
- Carat: the weight of the diamond (1 carat = 0.2 grams). Larger diamonds are rarer and more valuable per carat.
- Colour: graded from D (colourless) to Z (light yellow/brown). The less colour, the more valuable (with the exception of fancy-colour diamonds, which are valued for their intense hues).
- Clarity: graded from Flawless to Included, based on the number, size, and visibility of internal and surface characteristics.
- Cut: the quality of the diamond's proportions, symmetry, and polish. A well-cut diamond returns maximum light to the eye, creating the fire and brilliance that diamonds are prized for.
A diamond grading certificate from a reputable laboratory (such as the GIA, HRD, or IGI) provides an objective assessment of these criteria and is essential for accurate valuation of diamonds above approximately 0.5 carats. Our selling your diamond ring: the 4Cs guide walks you through exactly what each grading criterion means for your stone's market value. You may also find it helpful to understand what happens to your diamond after you sell.
Colour, Clarity, and Cut for Coloured Stones
Coloured gemstones are valued differently from diamonds. Colour is by far the most important factor, and the most desirable hue, saturation, and tone for each gem type commands the highest prices. A vivid, evenly saturated ruby will be worth many times more than a pale, unevenly coloured one of the same size.
Clarity is less critical for coloured stones than for diamonds. Some inclusions are expected and even desirable (silk inclusions in sapphires can enhance colour; the "jardin" of an emerald is part of its character). However, inclusions that affect durability or transparency will reduce value.
Cut affects how well the stone displays its colour, and a well-proportioned cut maximises both beauty and perceived size.
Certified vs Uncertified Stones
Gemstones accompanied by a laboratory certificate from a respected gemological laboratory (GIA, Gubelin, SSEF, Lotus Gemology) are easier to value and typically sell for more than uncertified stones of comparable quality. A certificate confirms the stone's identity, treatments, and, for high-value stones, potentially its geographic origin.
If you have an uncertified stone that you believe may be valuable, a professional valuer can advise on whether obtaining a laboratory certificate would be worthwhile. It is also worth understanding the difference between insurance valuations and resale value, as insurance certificates often state figures far above the market selling price.
Origin Premiums
For certain gemstones, geographic origin commands a significant premium. Burmese rubies, Kashmir sapphires, and Colombian emeralds are considered the finest examples of their type and sell for dramatically more than comparable stones from other sources. Proving origin requires specialist laboratory analysis and a certificate from a respected lab.
Getting Your Gemstones Valued
Whether you have inherited gemstone jewellery, received it as a gift, or simply want to know what a piece is worth, a professional in-person valuation is the most reliable way to determine value.
Why Professional Valuation Matters
Gemstone identification and valuation is a specialist skill. Many coloured stones look similar to the untrained eye. A red garnet can resemble a ruby, and a blue topaz can look like a sapphire. Professional gemologists use a combination of visual examination, refractometer readings, specific gravity measurements, and spectroscopic analysis to confirm identity and assess quality.
An in-person valuation also allows the assessor to examine the mounting, check for damage or wear, and assess the overall presentation of the piece, none of which can be done from a photograph.
South Coast Jewellers' Gemstone Expertise
At South Coast Jewellers, our home-visit valuation service includes expert assessment of gemstone jewellery. With over two decades of specialist experience, we bring professional testing equipment directly to your home and examine each piece carefully, identifying the stones, assessing their quality, and considering the current market for comparable items. Our valuations are free, no-obligation, and conducted in the privacy of your home by enhanced DBS-checked and fully insured staff.
Our expertise goes beyond simply weighing precious metals — we recognise the designer, antique, and collectible premiums that can make a gemstone piece worth significantly more than the sum of its parts. Whether you have a diamond engagement ring, a string of pearls, a sapphire brooch from your grandmother, or a collection of gemstone rings accumulated over a lifetime, we would be pleased to provide an honest and informed valuation. If you have inherited a collection, our estate jewellery guide for families offers practical and compassionate advice.
If you would like your gemstones or diamond jewellery valued, get in touch with South Coast Jewellers to arrange a free home visit anywhere across Dorset, Hampshire, and the wider South Coast. We visit homes in Bournemouth, Poole, Southampton, Portsmouth, Winchester, and the surrounding towns. You can also learn more about selling your gemstones and diamonds or read our home visit service guide to see exactly what to expect. We actively encourage customers to get multiple quotes — we are confident our prices compete. Our friendly team will handle your precious stones with the care and expertise they deserve, and provide a fair assessment of their value at current market rates, with immediate payment by bank transfer or cash if you choose to accept.