Choosing a diamond is a deeply personal and meaningful decision. At JCO (London) Diamonds, we believe that an informed choice leads to a confident purchase.
Our Diamond Guide has been carefully created to help you understand what truly matters when selecting a diamond, from quality and craftsmanship to ethics, certification, and long-term care.
The 4Cs of Diamonds
The beauty and value of a diamond are determined by four key characteristics, internationally recognised as the 4Cs:
CARAT
Carat refers to the weight of a diamond, not its physical size. While larger diamonds are naturally rarer, carat weight should always be considered alongside cut, colour, and clarity to achieve the greatest visual impact.
A well-cut diamond with balanced proportions can often appear larger and more brilliant than a heavier stone with inferior craftsmanship.
CLARITY
Clarity measures the presence of natural inclusions and surface blemishes within a diamond. Most inclusions are microscopic and invisible to the naked eye, meaning they rarely affect a diamond’s overall beauty.
Clarity Grades
FL • IF • VVS • VS • SI • I
At JCO (London) Diamonds, every diamond is carefully assessed by our specialists to ensure exceptional brilliance, beauty, and durability.
COLOUR
Diamond colour refers to how colourless a diamond appears. The less colour present, the rarer and more valuable the diamond tends to be, as colourless diamonds allow maximum light reflection and brilliance.
Colour Grades
D (Colourless) → Z (Light Yellow or Brown)
We carefully select diamonds that offer the ideal balance between beauty, quality, and value.
CUT
Cut is widely considered the most important factor affecting a diamond’s brilliance and sparkle.
A beautifully cut diamond reflects light with exceptional fire and scintillation, while even a high-quality diamond can appear dull if poorly cut.
Cut Grades
Excellent • Very Good • Good • Fair • Poor
At JCO (London) Diamonds, we prioritise beautifully proportioned diamonds that maximise brilliance and light performance.
Oval
Elegant and elongated, the Oval cut creates the illusion of greater size while beautifully elongating the finger. It combines the brilliance of a Round Brilliant cut with a refined and graceful silhouette.
Cushion
Recognised for its soft corners and pillow-like shape, the Cushion cut combines vintage charm with contemporary brilliance. Its romantic appearance and gentle sparkle make it a timeless favourite.
Princess
Modern, bold, and exceptionally brilliant, the Princess cut features clean lines and sharp corners for a contemporary aesthetic with remarkable sparkle.
Pear
Combining the elegance of Round and Marquise cuts, the Pear shape creates a graceful teardrop silhouette. Its elongated design offers a flattering and sophisticated appearance.
Emerald
Sophisticated and understated, the Emerald cut features long step-cut facets that emphasise clarity, depth, and elegance over intense sparkle. It is ideal for those who appreciate timeless refinement.
Marquise
With its elongated shape and pointed ends, the Marquise cut maximises perceived size while creating a dramatic and distinctive appearance.
Asscher
The Asscher cut is admired for its square shape and deep step facets, creating a mesmerising hall-of-mirrors effect with strong Art Deco influence and timeless elegance.
Radiant
Blending the elegance of an Emerald shape with the brilliance of a Round cut, the Radiant cut features trimmed corners and exceptional sparkle for a modern yet versatile look.
Heart
A true symbol of love and romance, the Heart shape is both meaningful and distinctive. When expertly cut, it displays beautiful brilliance while making a deeply personal statement.