Rare Stones & Coloured Diamonds

In gemmology, rarity has a more precise meaning than simply being expensive or fashionable. A stone can be considered rare in three distinct ways.

1. Rarity by locality Some gemstones are found in only one place on Earth. When supply depends on a single deposit, availability is naturally limited. Tanzanite is a classic example, sourced only from one region of Tanzania.

2. Rarity by limited production A stone may be rare because very little of it exists or reaches the market. Pink diamonds are a powerful example. Only a minute fraction of all diamonds display natural pink colour, and for many years the world’s primary source was the Argyle mine in Australia, which has now closed.

While diamonds are mined in greater volumes today than in centuries past, the vast majority are industrial or lower-grade material. Fine gem-quality diamonds represent only a small percentage of global production, and natural fancy colours such as pink occur in an exceptionally small proportion of those.

3. Rarity by exceptional quality Today, this is often the most meaningful form of rarity. Even when a gemstone type is relatively available, stones of outstanding size, colour, clarity and cutting precision are statistically exceptional. Although diamonds are not rare as a broad category, truly extraordinary diamonds are.

In essence, rarity is a spectrum. It can relate to where a stone comes from, how much exists, or how seldom nature produces something close to perfection.

Our approach blends rigorous gemmological understanding with instinct refined over generations.

We begin with facts. Geological origin and locality are examined carefully, particularly where supply may be finite or restricted to a single region. We consider historical production levels and whether availability has declined over time. Laboratory reports and certification are reviewed where appropriate to confirm authenticity, treatments, colour origin and measurable quality factors.

We are also deeply connected within the trade. Ongoing dialogue with trusted dealers, cutters and specialists across the world gives us real-time insight into what is genuinely scarce and what is simply fashionable. This constant communication allows us to understand not only what exists, but what is in short supply at a particular moment, and at what level of quality.

Beyond documentation, we assess the stone itself. A certificate provides important data, but it does not tell the full story. On paper, a stone may present as exceptional, yet in reality lack vitality due to nuances in cut, light return, transparency or internal structure. We examine how the stone handles light, how it moves, and whether it possesses the life and balance that statistics alone cannot convey. Years of experience allow us to identify these subtleties quickly and confidently.

Finally, there is judgement that cannot be quantified. Generations of Blacklock jewellers have handled exceptional stones and understand the difference between “very good” and genuinely rare. Decades of exposure to fine material cultivate a trained, instinctive eye.

The term rarity is never used lightly. It is a considered conclusion, assigned carefully and only when evidence, market context and experience align.

Colour is the most expressive quality of a gemstone. We look for saturation that feels alive, harmony across the stone, and a hue that remains compelling in varied lighting. Exceptional colour is unmistakable: it holds your attention before you’ve had time to analyse it.

When assessing colour in diamonds, context is everything. In white diamonds, purity of colour remains paramount, with the most colourless stones prized for their brightness and clarity of light. In fancy coloured diamonds, colour saturation and intensity becomes the focus, with grades such as 'Fancy Intense' often the most sought after.

However, greater saturation does not automatically equate to greater beauty; in certain hues, a 'Fancy Vivid' can appear overly strong or mask the stone’s natural balance. Each diamond must therefore be judged on its own merits, with a critical eye applied to colour, tone, and how the stone performs in light.

Craft has the power to elevate fine material into something truly exceptional. A master cutter does not simply reveal what is already there; he refines proportion, balances facets and calibrates angles with microscopic precision until light behaves exactly as it should. In doing so, very good material becomes rare not because of its certificate alone, but because of the extraordinary quality of its cut.

Chris Blacklock once examined two stones side by side. One was D colour, IF clarity with an excellent cut. The other was G colour, VS clarity, cut to within 0.01mm of perfection. The superior stone was the G colour, VS clarity example.

Its precision of proportion unlocked a level of brilliance and life the technically purer stone could not match. A fine cut enhances everything: brilliance, balance, and the way a stone gathers and releases light. A well cut stone reveals personality; a poor cut diminishes even the rarest material.

We assess cut through symmetry, polish and, most importantly, how the stone performs when rotated slowly through natural daylight.

Clarity contributes to value, but its role varies by gemstone. Some stones are prized despite inclusions, while others demand exceptional transparency. An emerald, for example, may carry fine ‘jardin’ — inclusions that speak to its natural formation and origin — without diminishing its beauty.

A diamond, by contrast, relies far more heavily on clarity, where inclusions can interrupt the passage of light and compromise brilliance. Our task is to determine whether clarity enhances beauty or detracts from it.

The Blacklock family has spent generations identifying extraordinary stones long before they reveal their worth. In the 1970s and 1980s, Ellis Blacklock and Ralph Blacklock would embark on buying trips to the Far East and beyond, travelling to bustling gem markets, mines, and workshops where exceptional stones first came to light.

These journeys involved painstaking inspection of raw and cut gems, negotiation with local merchants, and the cultivation of trusted relationships that ensured access to the finest and rarest material. It was on these trips that the foundations of our expertise were laid, shaping a business defined by instinct, discernment, and an enduring commitment to sourcing stones of unparalleled quality.

These stories are not exceptions. They are our inheritance.

For certain gems, such asKashmir sapphires, Burmese rubies, and Colombian emeralds, provenance can elevate a stone beyond rarity alone, transforming it into a piece of history. In these cases, origin is not merely geographic; it reflects distinctive geological conditions, historic deposits, and centuries of reputation. It becomes part of the narrative — shaping desirability, influencing connoisseurship, and contributing meaningfully to long-term value.

We work with respected independent laboratories when appropriate, ensuring clients receive transparent, independently verified information on origin, treatment and quality. For coloured gemstones, reports from SSEF, GRS, or Gübelin — widely regarded as the pre-eminent authority — provide essential clarity on provenance and enhancement. For diamonds, certification from GIA or HRD remains the international benchmark.

Certification is a valuable tool in navigating rare material — though never a substitute for informed judgement.

We work directly with the same trusted stone dealers who supply the world’s leading jewellery houses, yet we operate with the independence that allows us to secure stones at fair market prices.

Without the vast overheads of larger luxury houses,we are able to buy exceptionally and pass that value on to our clients. You receive the highest calibre of gemstones, withpricing grounded in fairness, transparency, and deep market understanding.Get in touch today for a prompt and discreet virtual consultation.