Diamond Spread and Cut Ratios

Everything you need to know about spread diamonds and diamond cut ratios

When purchasing a diamond, it can be helpful to do some research and learn a little about the characteristics that determine the quality of a diamond. This is particularly the case when purchasing a diamond as an investment, in order to ensure the quality of the diamond matches the purchase price, maximise its investment potential and guarantee the return on investment.

The 4 C’s of Diamond Grading

The 4 C’s of Diamond Grading

Most people are familiar with the 4 C’s of diamond quality, even if they are not aware of the particulars of each characteristic. The GIA’s 4 C grading system evaluates a diamond against four variables –Cut, Clarity, Colour, and Carat weight. It is this grade that determines both the quality and value of a diamond.

Diamond cut

The cut of a diamond is one of the most important factors in determining its attractiveness. A diamond cut to ideal proportions, with well-placed and well-shaped facets and a high-quality polish, allows the best refraction of light. The best quality diamonds are those that display the greatest brilliance, fire, and scintillation – essentially, the most sparkle.

The degree to which light is able to enter a diamond, bounce off the interior surfaces and reflect upwards to disperse through the top of the stone is completely dependent on how well the stone is cut. This is determined by the proportions of the stone, or its cut ratio, and the GIA has set dimensions for determining the cut grade of round brilliant cut diamonds.

Diamond cut ratios

Diamond cut ratios

A diamond’s cut ratio refers to its length to width ratio, calculated by dividing its length in millimetres by its width in millimetres. There are agreed parameters for ideal cut ratios, which differ between the various diamond shapes, such as pear and oval shape and emerald and cushion cuts.

How does a diamond’s cut ratio impact its quality?

Diamonds with a cut that is too deep or too shallow have a depth that is not in optimal proportion to its width. This improper cut ratio does not allow light to accurately reflect off the bottom inner surface of the stone – that is, rather than the light bouncing back to the top of the stone, it leaks through the bottom, resulting in less brilliance and fire.

Diamond spread

Diamond spread

A diamond’s ‘spread’ refers to the combined qualities of its cut and carat weight, specifically, how large a diamond appears to be with respect to its carat weight. The stone’s carat weight refers to its actual weight, measured in points or grams; its spread refers to its ‘face up’ measurements, determined by the diamond’s depth and facets angles.

Even though stones may have the same carat weight, their dimensions and cut ratios may result in their appearing to be quite different sizes. Differences in depth and diameter width can cause a 2-carat diamond with a better spread to look substantially bigger than another 2 carat diamond with a smaller spread.

Diamond spread and cut ratio

The important factor to consider in looking at the diamond’s spread is its cut ratio. There is a big difference – but a fine line – between a good spread diamond and one that is considered a shallow cut, and it is reliant on the diamond cutter’s ability to optimise the cut of the diamond.

The goal is to cut and facet the stone in a way that maximises the face-up diameter (or length) while keeping its cut ratio within the accepted, ideal parameters. If the diamond cutter simply aims for the greatest length and pushes the dimensions of the diamond outside the agreed cut ratio parameters, the stone will be too shallow and less robust. The result will be a stone that appears larger, but has less brilliance and fire, and looks dull and lifeless.

How to calculate a diamond’s spread

One of the simplest ways to estimate whether a diamond has the right amount of spread is to calculate its depth percentage. The smaller the diamond’s depth percentage, the more likely it is that the diamond’s weight is spread across its face-up diameter, giving the stone the appearance of being larger.

While the basic depth percentage can be estimated using the length (height) measurement of the diamond, there are other factors to consider when evaluating a diamond’s spread. A more comprehensive calculation of the total depth percentage, which takes the diamond’s crown and pavilion heights, girdle thickness, and light performance into account, will give a more accurate assessment.

Is a large diamond spread good or bad?

The crucial point here is not so much whether a large diamond spread is always ‘good’ or always ‘bad’. What is important is ensuring that the diamond has the ‘ideal’ amount of spread, to maximise its face-up measurements without compromising its strength or appearance.

While a larger diamond may be more desirable, and it can be tempting to choose a stone that appears larger than another stone of equal carat weight, selecting a stone with larger face-up measurements isn’t always the best option.

It can be helpful to remember that the GIA includes cut in its 4 C grading system because the quality of a diamond’s cut is incredibly important in determining its appearance and how well it performs the task of reflecting light, which directly impacts the stone’s value.

A truly well-cut diamond will rarely appear larger than its carat weight, nor will it need to. Its inherent beauty will be enhanced by an excellent cut that makes the most of its ability to reflect and interact with light, rather than being compromised by a shallower cut that maximises its face-up diameter but detracts from its refractive capabilities.

The take-away message here is that bigger is not always better – and this is definitely the case when purchasing an investment diamond. As a rule of thumb, do not sacrifice brilliance, sparkle, and character for the sake of spread.

Argyle Diamond Investments – where you will never need to trade sparkle for spread

Argyle Diamond Investments Pty Ltd offer the largest selection of investment-quality Australian pink diamonds sourced from, and certified by, Western Australia’s Argyle diamond mine.

Our pink certified investment diamonds are guaranteed to be of the highest quality, and at wholesale prices, our pink diamonds represent excellent value for money, meaning you will never need to choose spread over sparkle.

To find out more about pink investment diamonds call Argyle Diamond Investments on 02 4927 0000 or email us at info@pinkdiamondinvestments.com.au. Alternatively, fill out our contact form to book a VIP viewing of our in-store collection, or to have an Argyle Diamond Investments Pty Ltd representative contact you.

Argyle Diamond Investments Pty Ltd are Australia’s largest supplier of Australian certified pink diamonds and have exclusive use of the Australian Pink Diamond Analytics program. This program is a data driven decision maker that tracks and statistically analyses the rarity, financial growth and value of all investment grade pink and blue diamonds. With this valuable information, Argyle Diamond Investments Pty Ltd can offer all clients an investment grade pink from $5,000AUD up. But, the highest growth diamonds, are the larger, stronger colour pinks starting from around $20,000AUD plus.


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