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Diamond Refractive Index: Do Diamonds Disappear In Water?

Diamond Refractive Index: Do Diamonds Disappear In Water?

When you view your diamond, you can see the magnificent brilliance and sparkle that your stone exhibits. But have you ever wondered what would happen if you sink your diamond in a glass of water? Would you be able to see that same gorgeous sparkle? 

Now, we probably got you wondering: Do diamonds disappear in water?

The refractive index of a diamond is much larger than that of water, which means you will still be able to see your gemstone sparkle underwater – unlike glass, for instance, which has a similar refractive index to water. 

But why do diamonds sparkle in the first place? Answers to this – and many more questions – are all covered in this article, so without further ado, let’s dive in!

Diamond Brilliance: What Makes Diamond Sparkle?

When diamonds are found and mined, they are not the well-cut shining gemstones that we see in jewelry shops. When found, diamonds have rough and opaque skin on top. 

When cutting and polishing a diamond, this outer layer is removed. Additionally, two critical factors are considered. 

The first is the refractive index of the stone, which is responsible for the diamond’s brilliance. Second is the stone’s dispersive power, which allows it to split light and reflect more colors to the viewer’s eyes.

The term scintillation brilliance is used for the arrangement and number of light reflections from the diamond’s internal facets that exhibit sparkle as the wearer of the gemstone moves around.

A diamond’s fire is based on the cut’s crown angle and height and the number and size of the stone’s facets. Therefore, the cut, angles, and faceting of the stone are all crucial in determining the beauty of the diamond. 

When it comes to diamond cut, be sure to look at the stone’s proportions and its measurements. That will help you decide between two stones of the same cut range.

A diamond’s brilliance is a pretty complex combination of angles and proportions. It represents the stone’s light return based on how the light enters the stone, bounces around, and returns to the viewer’s eyes.

And that brings us back to the matter of diamonds disappearing in water: 

They don’t because, while light will refract and strike the gem at a different angle, causing it to appear less sparkly in water, water is not enough to make diamonds lose all their sparkle and “disappear.”

The brilliance consists of several factors based on patterns and faceting. Poor light return from a diamond will lack beauty – they’ll look duller and lifeless.

Fire describes flashes of color resulting from spectral dispersion or separation of white light into primary colors. The reason you see purple, blue, red, yellow, etc., in a diamond is fire. The more colors, the better.

So, how are the brilliance and fire optimized in a diamond? 

It’s usually the combination of the girdle, crown angle, table facet, pavilion depth, culet, and total depth – so, basically, the diamond’s cut in general.

See Also: What Makes Diamonds Lose Their Sparkle?

Diamond’s Cut 101

Diamonds are cut to maximize the brilliance, fire, sparkle, and overall beauty of the stone. The cut is a measure of light performance as the light hits the surface of the stone. 

When light hits a diamond, it finds its way in, bounces around, and reflects within the stone, and, in the end, returns to the viewer’s eyes. That is the sparkle that you can see. 

The diamond’s cut directly affects the amount of light performance achieved. The location, size, angles, and shapes of facets determine the diamond’s sparkle.

Cut Scale

Once a stone has been cut and polished, its’ cut can be graded. GIA grades the cut by measuring the sizes and angles of the facets of the stone. These include diamonds crown, culet, girdle, depth, pavilion, and table. 

These factors come together to determine the cut’s quality and, therefore, its grade. Each diamond size and shape has an ideal cut proportion. If you want an ideally cut diamond, just ask one of the gemologists; they can point out several diamond options that have ideal proportions.

With that said, let’s look at diamond cut grades:

Fair And Poor

Diamonds with considerable light leakage earn grades Fair or Poor. These stones tend to leak significant amounts of light from being too shallow or too deep. This cut category represents around 35% of gem-quality diamonds. 

Be sure to avoid these stones as they won’t make for sparkling jewelry.


Well cut diamonds that capture light earn grade Good. These stones have some light leakage, but overall, they shine brightly. They can have noticeably bigger or smaller measurements than better-graded diamonds of the same shape. 

The top 25% of stones have this grade.

Very Good

Very well cut diamonds that capture nearly all the potential of the diamond earn the grade Very Good. These precious stones are very brilliant and have minimal light leakage. 

The top 15% of gemstone-quality diamonds have this cut grade.


Excellent is the highest grade that represents the top diamonds in the world. Diamonds with this grade are masterfully crafted and cut with such precision that they unleash maximum brilliance and sparkle. Little to no leakage occurs as light penetrates the stone. 

This category represents the top 3% of all diamonds.

Selecting Cut Grade

The cut is often considered the most important of the diamond’s 4C’s. And it makes sense: When choosing diamonds, it’s vital to ensure the light isn’t lost. 

Excellent cuts are the best choice; however, Very Good cuts offer more value. The difference in sparkle between these two is subtle but is noticeable when inspected side by side. 

We generally recommend maximizing the cut grade if your budget allows it.

Fancy shapes have a bit fewer restrictions because beauty is in the eyes of the beholder. But still, you can safely go for a lower grade with non-round brilliant diamond shapes. 

Excellent cut fancy-shaped diamonds are somewhat rare, anyway.

Ultimately, it’s up to you, and you should remember there are many more factors that impact the diamond’s appearance. You’re the one to decide on which characteristics and attributes matter the most to you.

Pricing Effect

Just like the other diamond C’s, the cut grade has a significant impact on pricing. Today, we can see the highest number of Excellent cut diamonds. The improvement of diamond production technology allows diamond cutters to be more precise in cutting practices.

With round brilliant cut diamonds, an excellent cut grade can have a 5-10% premium over the Very Good cut. The same goes for Very Good to Good. Fancy-shaped diamonds don’t have GIA assigned cut grades. 

That’s due to fancy-shaped diamonds having a variety of shapes, lengths, and widths.

Buying Tips

Try to maximize the cut grade of the diamond. It represents the diamond’s sparkle and can aid in masking lower clarity grades, color tints, and smaller-than-desired carat weights. 

You can find value in a Very Good cut grade that has most of the aspects of an Excellent cut grade but missed the mark due to a thick girdle or more prominent table facet, for example.

Finish: Polish, Symmetry & Facets

Other factors that impact the diamond’s cut grade are polish, symmetry, and facets. Diamonds are generally cut in two different ways – brilliant cuts and step cuts.

Brilliant cuts, most commonly round or princess cut diamonds, have the highest level of sparkle. They have more facets than step cuts and are triangular or kite-shaped. Brilliant cuts possess a high degree of sparkle and maximum scintillation and fire of a diamond.

Step cuts, such as emerald and Asscher cut diamonds, have sparkle and fire. However, it’s less pronounced than in brilliant cuts. They have facets that resemble a staircase and are relatively simple-looking. 

Step cuts are considered very elegant – but don’t reflect as much light as brilliant-cut diamonds due to having fewer facets. In addition, polish and symmetry are a result of the production process. The polish of a gem refers to how smooth the facet surfaces are. 

The other factor is symmetry which is the pattern and evenness of the shape, size, and location of facets. If the location of the facet is imprecise, it will impact the gem’s light performance – and, therefore, the cut grade.

Diamonds & Their Light Performance

A diamond’s cut is in charge of the brilliance and sparkle you can see. That sparkle is known as the gem’s light performance. The light performance consists of factors such as dispersion, reflection, and refraction. 

The more and better a diamond can reflect and exhibit light, the better of a stone it is – and it will sparkle more when set in jewelry.


When a diamond is tilted and rocked at different angles, some light will reflect on the surface of facets. This occurrence is known as reflection. Generally, around 17% of light is reflected by the diamond. 

Reflection should always be balanced. When facets are too big, we can see reflections either weaken or strengthen too much – this will cause the diamond to look dull and lifeless.


The ideal diamond is cut so that light enters, bounces around, and bends within the diamond, and in the end, leaves form the top of the stone. This occurrence is known as refraction. 

Diamonds have a refractive index of 2.41 which is relatively high and gives them their sparkly characteristics. The refraction is most noticeable with ideal cutting. When a diamond is well cut, light reflects perfectly within the diamond.

Learn More: Do Diamonds Refract Light?


If you ever noticed that a diamond isn’t all black and white, and you can see the primary colors reflecting within the stone, that’s due to dispersion. 

As the light bounces around within the stone, it bends – and then leaves the stone to go back to our eyes. While we’re at it, a diamond’s dispersion measures at 0.44.

This occurrence is commonly known as the fire within the diamond. The visibility of these colors is what gives diamonds their unique beauty. Other gemstones usually don’t have the same gorgeous dispersion that diamonds have. 

Why Does A Diamond Lose Its Sparkle In Water? 

Okay, now that we’ve talked a bit more about diamonds’ light performance and the factors that play into it, we’d like to get back to our initial question – do diamonds disappear in water? 

While this matter generally requires some not-so-basic knowledge of physics, we’ll try our best to keep things as simple as possible. 

Now, we already mentioned that if you were to drop a diamond and a piece of glass into a glass of water, one would sparkle – although noticeably less than usual – while the other would lose its sparkle entirely. 

So, why do diamonds lose some of their signature sparkling when submerged in water? 

Diamonds have a refractive index of approximately 2.4. For comparison’s sake, glass clocks in at about 1.5 – and water has a refractive index of 1.3. 

What does that tell you? Well, as we explained, when light enters a diamond, it reflects from its internal surfaces before it leaves the stone – all thanks to the small critical angle. 

But once you drop a diamond in the water, the critical angle gets increased, meaning less light will bounce around inside the stone – hence, lowering its sparkle. 

However, no, a diamond would still not disappear in water. How would you be able to do the water test to check if it’s real or not if it did? 

Final Word

Do diamonds disappear in water? 

No, they don’t. That’s because diamonds have a refractive index of 2.41 which is much larger than that of water which has a 1.3 refractive index. That means that diamonds are still able to sparkle underwater – although the sparkle might be a bit subdued.

The main reason diamonds sparkle is because of the interaction of light with diamond cut. The type and quality of the cut dictate how well light reacts with the diamond. The relative measurements of the stone’s facets substantially impact how the light performs when it hits the diamond.

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