Beyond the 4Cs: How Coloured Gemstones Are Actually Graded

Introduction

When you go to buy a diamond, you will come across familiar phrases like cut, colour, clarity and carat, the famous 4Cs. This is the easy and structured method of comparing two diamonds. Now when it comes to applying the same concept to coloured gemstones, things quite like domino effect falls apart quickly.

A Kashmir blue sapphire, a Columbian emerald or even a Burmese ruby doesn’t play by the same rules. These coloured gemstones don’t have the same uniform perfection. They are all about personality, origin, and subtle visual cues which doesn’t fit neatly into the rigid scale. This is where gemstone grading for coloured gemstones come to play. There is no singly grading system available for coloured gemstones which is universal.

Instead of a universal analysis, experts mostly rely on layered evaluation methos which combines science, trained observation and the experience altogether. This blog is here for you to understand the gemstone grading for coloured gemstones. Along with understanding how coloured gemstones are graded. This blog will break down the how this industry actually operates while examining these beautiful gemstones.

Why the 4Cs Don’t Work for Coloured Gemstones?

The 4Cs that is the colour, cut, clarity and carat weight was originally designed for diamonds. This evaluation is chemically consistent along with being relatively uniform in appearance. Coloured gemstones are the opposite of this evaluation and chemical composition. Each type of coloured gemstone has:

• A different internal structure.

• A different level of acceptable inclusions.

• A different colour expectations altogether.

Due to this there is no global standard grading system for coloured gemstones. Instead of assigning some fixed grades, the gemmological laboratories make sure to describe their characteristics in detail. This is where the first big shift occurs that you are not just looking at a single score, rather you are reading a complete profile f the gemstone.

The Real Foundation: The ‘Modified 4Cs’

Even though the rule of 4Cs don’t fully apply to coloured gemstones, they still act as a starting point for them. For these beautiful gemstones, gemmologists have expanded the criteria into a broader framework which includes the following things:

• Colour (most important)

• Clarity (context-based)

• Cut (beauty-driven, not standardized)

• Carat (less predictive of value)

• Origin

• Treatment

Naturally that the parameters extend the 4Cs, some professionals also have named this as the 5Cs or even the 6Cs of coloured gemstones. Further in the blog there is a proper breakdown of all these parameters which will help you understand these stones better.

Colour: The Heart of Gemstone Grading

One primary rule in gemstone grading is that colour drives value more than any other factor. Gemstones a not like diamonds where less colour is preferred rather, they are prized for their intense and vivid colour. The gemstone colour grading scale evaluates colour on three core components, those components being:

• Hue is the dominant colour which directly refers to red, blue, green, etc colour.

• Tone of the stone which is the lightness or darkness of the stone.

• Saturation is the intensity or purity of the colour in the gemstone.

For example, a premium quality blue sapphire will not just be labelled as blue, rather it would be described as:

• Medium-dark tone

• Strong saturation

• Slight violetish-blue hue

This is the layered description which forms the real gemstone colour grading scale even though it is not provided in a simple chart in reports. In this what the experts mostly look for is:

• Even colour distribution in the gemstone.

• No patchy areas or zoning in the stone.

• That the stone has strong but not overly dark saturation.

There needs to be a perfect balance in the gemstone as too dark coloured stone can lose its brilliance and on the same hand, too light can look washed out again losing its significance.

Read Also: Understanding Grading Scales Used in Gemstone Reports

Clarity: It Depends on the Stone

Clarity is not measured in the same manner as it is done in a diamond. Where inclusions in a diamond in not desirable, this is not the case for coloured gemstones. Inclusions are a part of authenticity of these gemstones and sometimes these are even desirable. For instance, an emerald is rarely ever seen without any inclusions and these inclusions have their own value. Similar is the case with rubies as well.

There are certain laboratories which uses a certain clarity grading practices, which are as follows:

• VVS (very, very slight inclusions)

• VS, SI, I

This clarity variants are loosely applied to coloured stones and vary according to gem type as well. A ‘slightly included’ emerald can be considered extremely valuable whereas the same clarity in a sapphire will lower its value.

Cut: Beauty Over Precision

Cut is a stagnant look towards coloured stones. The parameter is appropriate and a standard for diamonds but the same is not the case for the coloured stones. The reason behind the same is because priorities changes when it comes to coloured stone, they are as follows:

• They focus on maximising the colour.

• Their focus is on minimising visible inclusions in the gemstone.

• It is also on preserving the weight of the gemstone.

All these aspects combined leads to more variations in shapes and proportions.

Now the important bit is what actually matters while evaluating a cut, those are:

• Symmetry

• Proportions

• Light performance (brilliance)

• Face-up appearance

When talking about coloured gemstones, a perfectly symmetrical and cut stone has the chances of looking dull if the cutter doesn’t focus on optimising the colour. This the reason why a cut in coloured gemstones is judged visually and not mathematically.

Read Also: How GIA Certification Impacts Global Gemstone Pricing

Origin: The Hidden Value Driver

Origin is one criteria for coloured stones where the gemstone origin grading becomes critical. Origin plays a vital role, for instance two identical looking stones can varied price range all because of its origin. some of the examples of the same is as follows:

• Kashmir sapphires are known for their velvety blue colour.

• Burmese rubies are famous for their ‘pigeon blood’ red.

• Colombian emeralds consist of vivid green colour along with high transparency.

There are various laboratories that determine the origin by using advanced testing however not all stones receive these origin reports.

The reason why theses origin matters is because:

• Rarity

• Historical reputation

• Market demand

Origin is not listed as a ‘grade’ in a report mostly, but it is a strong influence of changing a stone’s price and desirability amongst people with knowledge about the said topic.

Treatment: The Make-or-Break Factor

Mostly all the gemstone in the market used in a jewellery item is treated in some way or the other because is flawless coloured stone is rare and is investor piece. Those kind of pieces demand extra price as well. Some of the treatments done to these stones are as follows:

• Heat treatment is quite common in sapphires.

• Oil filling is common in emeralds.

• Diffusion or dyeing is a common practice and is a lower value treatment.

Now that we know of various treatments, let’s see how these affect the grading of the coloured stones. Untreated stones as mentioned are rarer and commands significantly higher prices. This is the reason why reputable laboratories always disclose the treatments done to a gemstone, making this a crucial part of the grading system for coloured stones.

Transparency, Lustre, and Optical Effects

Coming to the other factors apart from the 4Cs includes things like transparency, lustre, and optical effect in the coloured gemstones. Some of the things that experts evaluate are as follows:

• Whether the stone is transparent or translucent.

• What is the surface reflection quality of the gemstone.

• They also look at the optical phenomena like the star (asterism), colour change and the chatoyancy (cat’s eye) of the stone.

These are some of the elements that do not necessarily appear as grades in the report but greatly influence the value and classification of the gemstone.

Why There’s No Universal Grading System?

The honest truth to the answer of not having a universal grading system for coloured gemstones is because there can’t be one. Each gemstone has varied characteristics, and they behave differently accordingly as well. For instance;

• Emeralds are known to be naturally included and are valued for the same.

• Sapphires on the other hand are typically cleaner.

• Opals are known for their play-of-colour and not clarity.

This is the reason why labs majorly focus on descriptively reporting instead of sticking to rigid scoring systems. You will not be getting a grade like A+ rather you will get a detailed report.

How to Read a Coloured Gemstone Report

The easy method of reading a coloured gemstone report is:

• While looking for colour description look for terms like strong saturation, balanced tone, and desirable hue.

• In terms of clarity look for terms; is it eye-clean or does the inclusion affect durability of the stone.

• Always look for treatment disclosure whether the stone is natural or treated.

• If origin is added in the report, then it adds value to the stone.

• Lastly, the overall appearance of the stone as it matters the most.

The Biggest Mistake Buyers Make

The biggest mistake while looking at a coloured gemstone report is to apply the diamond logic to it. A pale blue sapphire will always value lesser than a blue sapphire with vivid blue colour. This is what flips the traditional clarity-first mindset altogether.

To understand how coloured gemstones are graded you will have to change your thinking from perfection to character.

Conclusion

To conclude we can say that gemstone grading for coloured gemstones is not about ticking any boxes rather is about interpreting a combination of factors. Those factors include how the colour dominates, clarity being contextual, cut is artistic, and the origin and treatment done to the stone adding layers to its value. The coloured stone not having a universal checklist is what makes them interesting and fascinating to work with.

Where diamonds are all about precision a coloured gemstone is more about nuance. Once a person understands this concept is when you start seeing it as an expert. That is when you will understand its geology, time, and human craftsmanship and stop categorising it as a product with grade.