What Does the Term Diamond Spread Means?

comparison of spread in two 1 carat diamonds

Loose Diamond On Grippers

There are several stereotypes attached to diamonds. Whenever discussion topics about these gemstones are brought up, people instantly think of sparkling, exclusivity jewels, money and many other romantic ideas.

In another paradigm of thought, one must expect eminent quality when buying diamonds. But what exactly is “eminent quality” and how do you define quality? 

A diamond should be as big as possible, that much is clear. Also, a diamond should ideally be colorless, cut perfectly and they should not contain any blemishes or inclusions either.

However, no matter how much we talk about these common characteristics, there is usually only one that will set your gut feeling either to “I want this gemstone, right now!” or “Ah, let us look for another stone!”. This one feature is due to a difference in sparkle, brilliance and size.

What is Spread?

To put simply, spread determines how large a diamonds appears to be when viewed face up. By simplifying the formula, we can see that spread is a combination of the diamond’s diameter, depth, table size and girdle thickness.

Listing out the desired characteristics a diamond should have, the first thing we had mentioned was that it should be as big as possible. However, spread might not always have a direct relationship with the diamond’s carat weight. Instead, spread only represents how big the diamond appears to be.

asscher cut spread comparison

In the example above, both Asscher cuts are 1 carat in weight. Yet, the one on the left appears bigger to the eye because of its larger face-up measurements. As a result, it has a better spread than the one on the right.

How to Determine Whether Spread is Good For Us?

Spread can sometimes have detrimental effects on a stone’s appearance that even the untrained eye can tell if there’s something wrong with the diamond. However, there are certain scenarios (like online jewelry acquisitions) where you are not given the chance to actually view the stone.

To help you make estimations, you can use the depth percentage of the diamond as a rough reference. You see, depth percentage is usually in an inverse relationship to spread. A smaller depth percentage usually means that the weight of the diamond is distributed sideways. This results in a wider and bigger looking diamond.

For “ideal” depth proportions, you can refer to the tables found at the respective sections for the various diamond shapes. To get a better metric for estimating spread, factors that make up the total depth percentage like girdle thickness, crown heights and pavilion heights should be taken into account.

A Deeper Look At Details

The trickier aspect which influences how weight is distributed across the diamond is girdle thickness. Without a Sarin report or Helium scan, it is almost impossible to gauge how much weight is taken up by the girdle thickness. For example, even if you see a very thin to very thick girdle description in a lab report, it tells you nothing concrete about the details.

Is the girdle very thin at only 2% of the girdle and 98% of the girdle is thick? Or is the girdle very thin at 90% around the diamond and 10% very thick at certain portions? Obviously, the diamond will have better spread in the latter scenario.

Likewise, weight retention methods like the use of pavilion bulges in step cut diamonds can make a diamond look smaller. In these cases, even though the diamond might exhibit a low depth (e.g. 57.0%), it doesn’t necessarily translate into better spread because its weight is now retained at the pavilions!

There Two Things You Should Keep In Mind:

louping a diamond for quality

Inspecting a Diamond For Quality

1. A depth percentage value between 58% and 62.8% is required for round brilliants to exhibit good brilliance. Note that these values are not minimum or maximum values. Based on observations, when round diamonds are cut to depths lower than 58% or over 62.8%, it usually leads to problems in optics.

If we go beyond both extreme ends of the spectrum, the beauty of the stone could be severely undermined due to the occurrences of fish-eye effects or dark nail head appearances.

2. Deciding whether the spread of a certain stone fits your needs based solely on total depth percentage can become tricky. There are a number of practices (e.g., changing girdle thickness with painting or digging) that do affect depth percentage while not affecting spread.

A better way to consider spread is to make use of the carat size charts and extrapolate the dimensions of a particular carat weight to its given shape.

What is the Problem With Shallow Cut Diamonds?

At a first glance, you might think that maximizing spread is something every cutter dreams of. After all, this appears to be a win-win situation because the consumer gets a bigger looking gemstone for a smaller carat weight. While diamonds with a high spread have the advantages of appearing bigger, they will also lose their sparkle and brilliance as a trade-off.

round diamond spread comparison

Even though the diamond on the right has better spread, it’s obvious that the one on the left is a better choice.

Remember, cut is king. Sacrificing brilliance for spread isn’t a smart idea. You can do your own exploration and research at JamesAllen.com by comparing diamonds with different depths.

Spready diamonds are still “desirable” to some degree since size does matter to consumers. However, I personally treat them like cheaters amongst diamonds. Truly well cut diamonds seldom appear larger than what they really are due to the physics of how light interacts with the facets.

On a closing note, diamonds are like the queens of jewelry. Imagine the Queen of Great Britain bragging in a swashbuckling manner like “Ha, I am the queen and you are not!”. To put in simple words, spread diamonds are the braggarts among gemstones. They appear to look big on a first sight but when examined closely, they lack sparkle and character.

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  1. Rafael Herman-
    July 10, 2018 at 3:21 am

    Do the spread diamonds have windowing effect due to the shallow cut?
    And on the other side, what brings lapidarists to cut gems very deep, if the gem appears to be smaller and it gives issues like light leakages and black spots?

  2. Paul Gian-
    July 10, 2018 at 3:47 am

    It depends on the degree of spread. In essence, the answer would be yes. As diamonds get shallower, the windowing effect becomes more pronounced. Profits is the main reason why lapidarists cut gems for weight retention because that’s what the general market values most at the moment.

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