The basic criteria determining a diamond's value are the so called 4Cs: colour, clarity, cut and carat.
Diamond colour ranges from D to Z, with D being the most colourless and hence the most desirable grade. There is little difference detectable by the naked eye between the colours ranging from D to F which tend to look colourless face up. Metal colour of the piece a diamond is set into will also affect its appearance, with yellow and rose gold lending the diamond its hue, and white gold and platinum accentuating the crispness of a colourless diamond.
Some people like the ‘warmth’ of an I, J or K colour. Within a given budget, you should seek the best balance of clarity, cut and carat to find the perfect diamond for you.
Diamond clarity is the other important determinant of its value. The fewer flaws and inclusions, the more valuable the diamond will be, with clarity grade ranging from the extremely rare F (Flawless), to rare VVS (Very Very Slightly included), VS (Very Slightly included), SI1 (Slightly Included 1), SI2 (Slightly Included 2), SI3 (Slightly Included 3), and I (included), which will have inclusions visible to the naked eye. SI2 is a borderline clarity grade where inclusionsmay become visible to the naked eye. The character of inclusions plays a big role in determining the diamond's value also - two diamonds of SI2 grade might look very different face up, depending on whether the inclusions are colourless (eg crystal needles, feathers, etc) or black. Two diamonds that are the same on paper may look very different in real life.
Cut has perhaps the biggest effect on a diamond’s beauty. The better quality the cut, the more brilliance and beauty the diamond will have. Diamond cut is highly technical, with given percentage ranges determining depth of crown, pavilion, their angle, facet length, etc. A diamond that is cut too shallow to maximise its face up spread will have poor light return. A diamond that is well proportioned and symmetrically cut, will have superior brightness (the measure of light reflected from a diamond), fire (the scattering of white light into all the colours of the rainbow) and scintillation (the amount of sparkle that a diamond has, and reflections inside the diamond resulting in a particular pattern of dark and light areas), resulting in a more beautiful diamond.
Diamond carat is the standard used to measure diamond weight. A carat equals 1/5 of a gram. As diamonds increase in size, their cost tends to increase exponentially. Weight does not always enhance the value of a diamond – particularly if it is cut badly. Indeed a good cut can enhance the perceived size of a diamond.
For more on diamonds, go to our blog White Diamonds: Beyond the 4Cs.
Lab grown diamonds are not to be confused with diamond substitutes, such as cubic zirconia or moissanite. Grown in a lab, man made diamonds are identical in looks to the natural, mined diamonds, and are governed by the same grading system of colour, cut, clarity and carat. Lab grown diamonds represent better value for money than mined diamonds, costing on average 30-40% less, and have been gaining in popularity as a centre stone of choice in engagement rings.
For more on lab grown diamonds, go to our blog, Lab Grown Diamond Engagement Rings.
Salt and pepper diamonds have become a popular choice in contemporary engagement rings. Each one is unique due to its distinctive markings - carbon particles that never crystallised into diamonds. Salt and pepper diamonds share the same characteristics as white diamonds (although they are not governed by the 4Cs grading system like their colourless counterpart) and make a beautiful and durable engagement ring centre stone.
For more on these beautiful gems, go to our blog, Salt and Pepper Diamonds.
Sapphire is a valuable, gem quality corundum that is hard wearing, measuring 9 on the Mohs hardness scale, making it an ideal alternative to white diamond in a piece of jewellery worn every day, such as an engagement ring.
Sapphire is a true rainbow gem which occurs in various shades of blue (vivid royal blue and cornflower blue being the most valuable), black, green, teal, white, pink, orange, yellow, purple and pinkish orange (Padparadscha). For more on sapphires, go to our blog, Sapphire.
Some crystals also display two or more colours in the same gem - most commonly blue and yellow. Some crystals are cut so the colours mix into shades of green and teal, while others are cut to display more distinct colour zoning. These stones are called bi-colour, or parti sapphires. Australia produces some of the best parti sapphires, with most material found in New South Wales and Queensland.
For more on Australian parti sapphires in engagement rings go to our blog, Australian Parti Sapphires in Engagement Rings.
Spinel is a beautiful, valuable gem of excellent lustre and durability (7.5-8 on the Mohs hardness scale), making it a great choice for jewellery worn every day such as engagement rings. Spinel is often found in the same deposits as corundum (ruby and sapphire) but is more rare. Despite this, spinel is more affordable than sapphire or ruby. Spinel occurs in a wide array of colours, such as vivid blue, red, grey, pink, orange, teal, green, white, black and purple.
For more on spinel, read our blog, Spinel - a perfect gem for contemporary jewellery.
Emerald is part of “top three” coloured gemstone suite, along with ruby and sapphire. These highly coveted gems are prized for their beauty, exceptional colour and fascinating historical provenance.
Emerald, Be3Al2(SiO3)6, is the most precious green coloured gemstone and a member of the beryl gem family, whose members also include aquamarine, morganite, heliodor and goshenite. Trace amounts of chromium and vanadium give emerald its beautiful green colour.
For more on emerald, read our blog Precious Emeralds in Bespoke Jewellery.