Diamond grading is the process to evaluate a diamond’s quality based on the 4C’s. The four C’s are carat, colour, clarity and cut. While the four c’s and diamond grading is comprehensive, it does not cover every aspect of a diamond's appearance or characteristics. In this article, we will explore what diamond grading doesn’t include such as phosphorescence, hues, internal strains and striations and why these factors can significantly impact the appearance of your diamond.
What is diamond grading?
Diamond grading is a standardised process of evaluating a diamond's quality. Organisations like the Gemological Institute of America (GIA) and International Gemological Institute (IGI) evaluate diamonds based on the 4C’s.
- Cut: How well the diamond interacts with light from the arrangement and proportions of the diamond facets.
- Colour: The presence of colour, measured on a scale of D-Z
- Clarity: The number and size of internal and external blemishes and inclusions
- Carat: Unit of measurement to describe the diamond's weight, One carat is equal to 200 milligrams, or 0.2 grams.
Diamonds are assigned a grade for each factor, which describes the overall quality and appearance of the diamond.
Why was diamond grading introduced?
Diamond grading was introduced to establish a standardised system for evaluating diamonds. Previously jewellers would describe their best diamonds by A, AA, AAA , numerals 1, 2, 3, roman numerals or a combination of both. This led to confusion between customers. Robert M Shipley established the 4C’s in 1931 to protect consumers and maintain a standard for evaluating gemstones. Robert also established the Gemological Institute of America (GIA) in 1931 and is known today as the leading source of knowledge, standards and education in gems and jewellery. Jewellers began using the 4C’s in 1941 to describe a diamond’s features.
What isn’t graded for?
The four C’s do not cover everything. Defects such as phosphorescence, strains, striations, bowties, and tints/hues of the diamond, are not detailed in the grading report. These factors significantly impact the look of the diamond but are outside the traditional grading framework and not openly discussed. This is why you can have two diamonds graded identically but look very different.
Why are lab diamonds being grown with these defects?
The demand for lab grown diamonds has increased but a significant portion are being produced with defects. Many of these defects are intentional due to trying to produce as many lab diamonds as possible, as fast as possible, for as cheap as possible. This has created two lab diamond markets, good quality lab diamonds and bad quality lab diamonds. The problem is, consumers are unaware and purchasing based directly off the report from ecommerce websites who do not hold the stock or inspect it in person. Manufacturers unable to get rid of their poor quality lab diamonds chuck these on a database and are being sold directly to consumers through ecommerce websites.
Diamonds with phosphorescence (glow under UV light) are caused by boron impurities. Less than 0.1% of naturally occurring diamonds contain boron impurities, they are considered rare. Grading did not need to account for this previously as it was extremely rare to come across.
Blue Tinge
HPHT diamonds aren’t grown in a vacuum like CVD, making it harder to control the environment they are grown in. Nitrogen from the atmosphere (78%) is impossible/very difficult to remove from the growth cell, causing the diamond to turn a golden brown/bright orange. To get a colourless diamond the nitrogen must be removed. The easiest solution is to add boron. However, boron does not adhere to the growth cell uniformly, to prevent the brown/orange hues from the nitrogen, boron must be overcompensated for. If too much boron is added, the diamond turns a blue tinge.
What is Phosphorescence
Phosphorescence diamonds continue to glow after being exposed to ultraviolet (UV) light. Phosphorescence differs from fluorescence, which is noted on a grading report. Fluorescent diamonds glow under UV light but stop glowing once the UV light source is removed.
Phosphorescent diamonds can remain glowing for seconds or minutes once the light source has been removed. Phosphorescence is typically found in Type IIB diamonds, which contain the trace element boron. Type IIB diamonds are exceptionally rare to find in naturally occurring diamonds, less than 0.1%.
What causes Phosphorescent diamonds?
Phosphorescence in diamonds is caused by the presence of Boron. Boron is introduced to counteract the unwanted effects of nitrogen. Nitrogen is naturally present in the atmosphere, so it can be found in the diamond growth cell, or it can be deliberately added to speed up the diamond growing process (usually by 200-300%).
Boron is used to neutralise nitrogen. Boron does not uniformly adhere to the crystal so it must be overcompensated for. Too much can cause the diamond to turn a blue tinge/hue. The phosphorescent glow may not be even throughout the diamond because the boron does not uniformly adhere.
Type IIB diamonds are more likely to have a blue tinge however, not all Type IIb diamonds will have a blue tinge or phosphorescent glow. Some diamonds without a blue tinge will have a phosphorescent glow. This must be tested in person, there is no way to tell from photos or videos and it is not mentioned in the grading report.
Phosphorescent diamonds are not known to have any impact on the diamond’s quality or appearance in normal lighting conditions (some fluorescent light bulbs can set off the phosphorescent glow) however, it’s important to be aware of this trait if it’s something you prefer to avoid. If you like the look of this and want a diamond that glows, and think it’s unique and cool then this can be sourced, as long as you are aware of what you are purchasing.
Why is phosphorescent diamonds an issue?
Diamonds are electrical insulators and moissanite is an electrical conductor. Due to trace elements, different electrical properties can be given off. A diamond containing boron can give the result of synthetic moissanite on basic diamond testers. Synthetic moissanite can also test as diamonds as it has been refined over time to have lower electrical conductivity.
What are blue/grey/brown Tinges/Hues in lab diamonds? - colour grading
Colour grading assesses the presence of colour in diamonds when viewed from the culet-up. Diamonds are thought to be colourless (D) to yellow/brown (Z). However, with lab grown diamonds and the presence of trace elements, it’s important to note that the D-Z scale includes tinges, not just colourless, yellow and brown. Diamonds beyond the Z range are classified as fancy colour diamonds, which display notable colour when viewed face up.
A diamond with a D colour grading can look brown face up because of vacancies in the atomic structure. As the light reflects through the diamond, the atomic vacancies can cause the diamond to look brown. A diamond can look different face up vs culet up. It is nearly impossible to detect grey hues/tones in a 360 video.
How do these brown/grey defects occur?
Manufacturers are incentivised to run the machines faster, add agents that speed up the growth, reuse cheap materials and grow as many diamonds as possible for as cheap as possible to maximise profits. This creates ugly lab diamonds. To undo some of these side effects, other elements and treatments are added, which come at a cost and produce these brown/grey/blue defects.
To produce better lab diamonds, manufacturers would need to run the machines slower, source better quality seeds and materials which would come at a higher cost and not add agents that speed up the growth; however, this would affect profits and it’s easier and cheaper to grow the diamonds fast and then add treatments later on.
What are some ways blues/greys/browns can occur?
- Nitrogen: Accelerates the growth of diamonds by 200-300%, causes yellow, orange or brown tints
- Boron: Added to counteract the nitrogen, too much causes a blue tinge. Boron must be overcompensated as it does not uniformly adhere to the growth cell.
- Irradiation: Fixing a blue tinge HPHT diamond with irradiation can cause it to turn grey
- Running the machine too hot and fast: Can cause atomic-level voids, giving the diamond a brown appearance
- Graphite nano-clusters: Causes the diamond to appear grey. Can occur from post growth treating a CVD diamond, carbon atoms revert back to graphite bonds.
- Metal Inclusions: Adding aluminium and titanium agents can cause metal inclusions, making the diamond appear grey
- Pinkish brown: Nitrogen beside a vacancy/void in the crystal structure
Impacts of these defects:
Two diamonds with the same grade can look extremely different, with one appearing dull or grey.
Currently there are two lab diamond markets, good quality labs and bad quality labs. Manufacturers are struggling to get rid of the bad quality labs, which are often heavily discounted and listed on databases connected to retail websites. These diamonds are typically showcased with 360-degree videos and photos, but the quality and consistency of these visuals depend on the seller. It’s nearly impossible to judge a diamond’s true quality from these images/videos and grading reports do not report on defects such as bowties, phosphorescence, blue/grey/brown tints, strains and striations, leading to situations where consumers may unknowingly purchase lower-quality stones at seemingly “great prices.”
CVD Strains and striations:
Strain:
Looks like streaks of glass or blurriness. Strain is caused by using poor quality seeds. The carbon atoms do not evenly deposit onto the seed, causing the crystal lattice structure to deform, since the crystal lattice structure is not even, it affects how the light performs, causing birefringence, the light to scatter. HPHT treatment can improve strain.
Strain is not mentioned on a grading report.
Striation:
Diamonds with striation appear out of focus and dull. Striation looks like visible parallel lines or growth lines. Striation can occur from minor disruptions in diamond formation or from stopping and starting CVD reactors. CVD reactors have a viewport, so if manufacturers notice the diamond is not growing quite right, they can stop the reactor, make adjustments, then start the reactor again. However, the conditions and concentration of elements are at different levels and not consistent when you stop and start the reactor, causing striation.
All CVD diamonds have some level of striation, but it varies in levels of intensity, the more the CVD reactor is stopped and started, the worse the striation and the increased chance of the carbon atoms depositing incorrectly, worsening the look of the diamond.
Striation is not mentioned on a grading report, a diamond may be given a VVS1 grading but still have striation.
Bow Tie
Bow ties are dark connected triangles at the centre of elongated diamonds, they look like a bow tie. Bow ties are not mentioned on grading reports, you will need to examine the diamond in person to identify the strength of the bowtie. Bowties are common in elongated shapes but range in intensity. Bow ties can be caused by poor cut and symmetry.
Windowing
Windowing is when an area of the diamond is not returning light to the eye. Some facets rather than reflecting the light back, act as a window, allowing it to pass through. Step diamonds such as emerald tend to show windowing more than other shapes due to their large facets.
Diamond grading does not mention whether a diamond has windowing or to what degree, this must be inspected in person.
Why are these lab diamond defects a problem?
Jewellers aren’t aware of the defects common in lab diamonds. Reasons being, these issues aren’t graded for (which is not a valid excuse), they don’t know and haven’t been educated (not a good excuse). Businesses are making a larger margin on these cheaper lab diamonds by selling them among the nice ones, it’s like the lemon and the car yard dilemma. Jewellers aren’t curating and testing their own list of trusted suppliers, they aren’t inspecting every diamond in person and sending back the rejects. They are reliant on a database that can be connected to their website, also reducing the cost needed to invest in stock and curing their own list of suppliers. This leaves the choice and responsibility in the hands of the consumer who can’t avoid these issues or doesn’t know what to look out for, even if they wanted to look out for it, it’s not graded on, and a lot of these problems can only be discovered from inspecting the diamond in person.
In house grading:
Another issue facing the diamond industry is ‘in house grading’. Some lab grown diamond companies no longer need to send their stones to an IGI office for grading. IGI India has established laboratory setups inside the factories of high volume diamond growers. It’s not unusual for labs to do grading on site however, ‘in factory’ operations could create the appearance of a bias.
“While we conduct quality checks and periodic calibration of our gemologists to reassess and adjust their grading techniques, such measures may not be effective in preventing all instances of grading errors or fraud by gemologists or third parties.” - Source
Why are consumers led to believe lab diamonds are inferior?
Some buyers believe lab diamonds are inferior and don’t sparkle as nicely as natural diamonds. Since the defects have become more noticeable and prominent in cheap lab diamonds, even non gem experts are able to see them, leading to this view. Jewellers will also tell consumers lab diamonds are inferior because they are either not informed on the defects and influence this has on the appearance or they want to try and persuade consumers to purchase a natural diamond.
With poor lab diamonds flooding the market, suppliers are struggling to get rid of them, they are being priced extremely low to free up capital as growing diamonds uses a huge amount of energy, people, machinery and resources. Some businesses are passing on the savings, while others are charging premium prices for poor quality lab diamonds. Consumers are questioning why there might be a 3-5x price difference and since the defects are not graded on, those not aware are not able to differentiate and are led to believe they are getting a ‘good deal’ on these cheaper defective lab diamonds, or these high-quality lab diamonds that are priced higher are not worth the price.
There is a current gap in knowledge, the problem is only going to get worse until consumers are more educated and demand better quality lab diamonds. Until then, it's the wild west trying to buy a good quality lab diamond online.
Diamond grading is essential for evaluating a diamond's quality, but it has limits, especially when it comes to lab diamonds. Grading has not been updated to reflect the defects and variances between lab diamonds. Characteristics like phosphorescence, grey/blue/brown tints and hues, strains, striations and bow ties are not included in grading reports, making it a gamble for the consumer to select a diamond online. It’s essential when choosing a diamond or engagement ring to choose a trusted jeweller (such as Henry Francis) who is knowledgeable, able to explain the nuances, what to look out for and is inspecting their diamonds in person before passing the choice onto the consumer.
