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Prestons Guide

Our Guide to Diamonds

Our guide to understanding the 4 C’s and how cut, colour, clarity and carat create the value and beauty of a diamond.

If you are looking to discover your perfect diamond, then you will first need to explore the 4 C's. The value and beauty of a diamond is attained by a combination of the 4 C's, four characteristics which are considered the most important when selecting your stone. Each of our showrooms would be delighted to guide you through the cut, colour, clarity and carat of our diamonds, advising and guiding you to the choice that is right for you.

Diamond Cut

The cut, often referred to as one of the four C’s, can be considered one of the most important in diamond grading. The cut refers to not only the shape of the diamond but the proportions of the gemstone itself. The proportions determine which angle the light enters and exits the diamond, projecting a glimmer of sparkle and fire throughout the stone.

Today, technological advancements have allowed diamond cutters to determine the exact characteristics of each stone allowing them to enhance the natural beauty of a diamond with minimal waste.

Diamond Colour

The colour of a diamond is important consideration when looking for your perfect stone. A good, or white, colour to your diamond will allow it to reflect more light and brilliance and therefore combined with the other 3 C's sparkle more.

The rarest and most valuable diamonds are completely colourless and rated as a 'D' in colour. Of course, the difference between two colour grades can be a significant difference to the price of your diamond. Our showrooms each offer a selection of 'D' colour diamonds and guaranteed to always only showcase diamonds graded as white, usually ranging from D-F but sometimes including G which is classed as nearly colourless.

Diamond Clarity

A diamond’s value comes from its own natural beauty as well as its rarity and clarity. Each natural diamond contains identifying characteristics, unless internally flawless, and the clarity of a diamond is determined by the degree to which a stone is free from these characteristics, often referred to as blemishes, inclusions, or flaws. The scale starts at IF, meaning internally flawless, through to I1 or I2, meaning the diamond is included to the 1st or 2nd degree with inclusions often visible to the naked eye.

Each diamond at Prestons is accompanied by a diamond certificate. This certificate will not only show you the grading, e.g. SI1, of a diamond but a description of the types of inclusions, or characteristics in your diamond.

Diamond Carat

The carat of a diamond refers technically to its weight but is also often associated with the size of the stone. A carat is a technical form of measurement, one carat is divided into 100 points, and therefore 0.75cts would translate to 75 points or 0.50cts to 50 points, as illustrated below throughout our enlarged scale.

The carat weight can also be affected by the cut of a diamond, for example an oval cut diamond presents a larger surface area than a round brilliant cut of the same carat weight, thus giving the appearance of a larger stone. The carat weight, although an important consideration, does not alone determine a diamond's value but instead a combination of all 4 C's.

Discover Prestons

Our showrooms in Guildford, Leeds and Wilmslow continue to offer the advice, guidance and service that has been our hallmark since 1869.

Our Showrooms

Over the years, generations of families have become customers of Prestons, and many have gone on to become friends. Today, our teams look forward to welcoming you to our showrooms in Surrey, Cheshire and Leeds.

Prestons Guildford


Our Guildford showroom, which is now located on the opposite side of the high street, is designed to reflect the architectural merit of the Edwardian building it now occupies. The store features newly extended spaces dedicated to the fine watch houses it showcases, alongside a comfortable lounge to allow our clients to explore our bridal and fine jewellery collections. Explore This Showroom

Prestons Wilmslow


Located in the heart of Wilmslow, this showroom features a selection of spaces dedicated to the fine watch houses it showcases. Of course, the bridal collections Prestons have always been famous for remain a prominent feature of the store and surround the famous Aquarium Bar which sits at its centre. Explore This Showroom

Rolex by Prestons, Leeds


This showroom, located in Victoria Gate, features extensive Rolex showcases alongside a discrete VIP lounge. Every element of the interior design radiates the values of the Rolex crown: excellence, precision and attention to detail from louvre walls in walnut, to the careful calibration of colours and patterns within the fittings and furnishings. Explore This Showroom
Guildford showroom