A diamond grading report is a vital document in the jewellery industry, offering a clear and unbiased assessment of a diamond’s characteristics. It provides a standardised framework for evaluating quality and value, ensuring buyers and jewellers alike have confidence in what is being purchased or sold.
For those selecting fine jewellery, such as Hatton Garden engagement rings, the grading report is especially important. It serves as an independent confirmation of a diamond’s attributes, allowing clients to make informed choices with clarity and trust.
This guide will explain how diamond grading works, exploring the recognised grading systems and the role of leading institutions such as the Gemmological Institute of America (GIA).
What is GIA Diamond Grading?
The Gemmological Institute of America (GIA) is widely recognised as the leading authority in diamond grading worldwide. Renowned for its expertise and rigorous standards, GIA has established the benchmarks by which diamonds are assessed.
GIA first devised its diamond grading system in 1953, introducing the 4Cs, which stand for colour, clarity, cut and carat weight. This created a universal language for evaluating diamond quality and set the global standard that is still trusted by jewellers and buyers today.
A GIA diamond grading report provides a scientific assessment of a diamond’s characteristics, offering an objective analysis of its qualities. Whilst the report does not declare a diamond’s value, these attributes are consequently used by jewellers and appraisers to help determine its price.
How Does Diamond Grading Work?
The Laboratory
Once a diamond has been cut, polished and faceted, it is ready for grading at the Gemmological Institute of America (GIA). The process begins with the polished stone being examined individually in a controlled environment designed for precision and consistency.
At the GIA, each diamond is assessed by multiple trained gemmologists to ensure accuracy and reliability. Typically, at least two graders independently evaluate the stone’s 4Cs: colour, clarity, cut and carat weight. If there is any disagreement, additional graders are consulted until a consensus is reached.
The grading takes place in a meticulously controlled laboratory setting. Diamonds are examined under daylight-equivalent fluorescent or LED lighting to provide a standardised view of colour and brilliance. Specialised viewing stations with neutral grey backgrounds minimise reflections and distractions, while high-powered magnification tools allow gemmologists to inspect every inclusion and facet with precision. Observations are recorded in detail, resulting in a report that reflects the diamond’s scientific qualities rather than any personal opinion.
Grading Reports
A diamond grading report is a formal document issued by the GIA after a diamond has been assessed. It comes as a paper certificate and is also stored in GIA’s online database, allowing buyers to verify authenticity and view the diamond’s details at any time.
The report records more than the 4Cs of colour, clarity, cut and carat weight. It includes measurements, proportions, polish, symmetry and any fluorescence. Some GIA grading reports also feature a plotted diagram showing inclusions and blemishes, though this is not included on every type of report.
Many GIA graded diamonds are laser inscribed on the girdle with their unique report number. The inscription, visible only under magnification, permanently links the diamond to its certificate and provides buyers with added assurance.
Universal Communication
The diamond grading system provides a consistent framework that allows jewellers, appraisers and buyers to discuss diamonds using a shared language. This clarity ensures that everyone can understand and compare a diamond’s qualities accurately, whether purchasing locally or sourcing from other markets.
By standardising terminology and grading criteria, the system supports transparency and trust in the jewellery trade, giving buyers confidence that the diamond they select matches its description and quality.
How are Diamonds Graded?
Diamond Colour Grades
Diamonds are graded for colour on a scale from D, which is completely colourless, to Z, where a faint yellow or brown tint becomes noticeable. In general, the less colour a diamond shows, the higher its value, as colourless stones are rarer and more sought after.
When selecting a diamond, it is important to factor in the colour of the ring setting, as this can affect how the diamond’s colour is perceived. If you are aiming for a colourless stone (D–F), setting it in platinum can help prevent the diamond from taking on a yellow or rosy hue from the warmth of gold. This does not mean that the rest of the band cannot remain gold, allowing for a combination of metals while preserving the appearance of a truly colourless diamond.
Diamond Clarity Grades
Clarity refers to the presence of internal characteristics, called inclusions, and external marks, known as blemishes, in a diamond. Clarity is assessed under 10x magnification, allowing graders to evaluate the size, number, position and visibility of each feature.
Diamonds are graded on a scale from Flawless (FL), which have no inclusions or blemishes visible under 10x magnification, to Included (I1-I3), where imperfections are easily seen and may affect transparency and brilliance.
For buyers seeking a balance between quality and value, diamonds that appear eye-clean, meaning they have no visible inclusions to the naked eye, often represent the most practical choice. This typically includes diamonds graded VS1, VS2 and SI1, though the appearance of inclusions can depend on the shape and cut of the stone.
Diamond Cut Grades
The cut of a diamond is a critical factor in its overall appearance, as it determines how well the stone reflects light, creating brilliance and sparkle. A well-cut diamond maximises its visual impact, while a poorly cut diamond may appear dull even if its colour and clarity are high.
Diamonds are graded for cut on a scale ranging from Excellent, Very Good, Good, Fair to Poor. It is important to note that GIA provides a formal cut grade only for round brilliant diamonds; other shapes are assessed for polish and symmetry but do not receive an official cut grade.
When reviewing a diamond grading report, prioritising cut quality is highly recommended. A superior cut enhances the diamond’s beauty and can make a noticeable difference in its visual appeal.
Diamond Carat Grades
Carat refers to the weight of a diamond, not its physical size, and two diamonds of the same carat can appear different depending on their cut and proportions. A well-cut stone may look larger and more brilliant than a heavier diamond with poorer proportions.
Diamonds are priced per carat, and the cost rises exponentially rather than linearly. For example, a 1.00ct diamond costs substantially more than twice the price of a 0.50ct diamond, assuming other quality factors remain the same.
When selecting a diamond, it is important to consider carat weight alongside the other Cs: colour, clarity and cut. Balancing these factors ensures the diamond achieves the best overall appearance and value.
Additional Diamond Grading Information
The Polish of a Diamond
Polish refers to the smoothness of a diamond’s facets after cutting and finishing. It affects how cleanly light interacts with the diamond’s surface and contributes to overall brilliance. Diamonds are graded for polish on a scale from Excellent, Very Good, Good, Fair to Poor. A higher polish grade indicates minimal surface blemishes, allowing light to reflect without disruption. Polish is recorded on the diamond grading report, giving buyers insight into the quality of the finishing work.
The Symmetry of a Diamond
Symmetry describes the precision and alignment of a diamond’s facets, including the relationship between its table, crown, pavilion and overall shape. Symmetry is graded in the same way as polish, from Excellent to Poor, reflecting the accuracy of the facet arrangement. Poor symmetry can cause light to leak from the stone or appear uneven, reducing sparkle and optical appeal.
The Fluorescence of a Diamond
Fluorescence is the visible glow some diamonds emit when exposed to ultraviolet light. It is graded on a scale ranging from None, Faint, Medium, Strong to Very Strong. While fluorescence does not affect the structural integrity of a diamond, it can sometimes cause a hazy or oily appearance. For this reason, many buyers prefer diamonds with no fluorescence. The level of fluorescence is recorded on the grading report, offering transparency regarding this characteristic.
Find Your Perfect Diamond with Rennie & Co
Understanding a diamond grading chart is key to making an informed purchase, giving you confidence in the quality, characteristics and value of your chosen stone. At Rennie & Co, we invite you to visit our Hatton Garden showroom to view GIA certified diamonds in person, allowing you to appreciate their brilliance and craftsmanship firsthand.
With a reputation for quality, Rennie & Co provides expert guidance to help you select the diamond that best suits your preferences and budget. To experience our personalised service and review grading reports with a knowledgeable specialist, we encourage you to book an appointment and explore our collection in detail.
