Good Diamonds vs. Bad Diamonds, Emphasis on Cut

The Four C’s Gone Bad - Diamond Cut

As a Santa Barbara Jeweler, I had the unhappy task of explaining to Marly and John, a nice young couple, why that center diamond they got online with the great appraisal certificate looked so lackluster.

I didn't like saying it and they didn't like hearing that it lacked the dispersion or sparkle necessary for daily wear.

Buying bad diamonds is a tragic event in any young couple’s love life. This is the first in a series of blogs written to help you avoid buying bad diamonds.

With Great Color and Clarity it’s Still a Bad Diamond With Bad Cut

Most of you have already heard of the 4 C’s when referring to diamonds: Color, Clarity, Cut, and Carat Weight. John had, but he was missing a little bit of the down low on cut. I’m going to talk about one of the most overlooked, yet most important C: cut.

Unlike the other three C’s that are measured by carat weight, color, or clarity grade, cut isn’t so easy to classify. Unless you’re an expert, you can’t just throw a diamond on a scale or look at it under magnification to discern its quality.

And seriously, two experts might not agree on its value! Before we get into how to go about telling a good cut diamond from a bad cut diamond, let’s first review some facts about diamonds.

Shape vs. Cut, Yeah, You Should Read this Part

Cut is different than shape. Shape is the basic form or outline of a stone. Examples of different shapes are: round, square, marquise, and triangular. Theses are all shapes.

Cut refers to the geometric proportions of a given shape.

Round shaped diamonds come in many different cuts. Despite what I just told you, you will still hear the words “cut” and “shape” used interchangeably. Don’t worry. Just know that a “round cut” diamond is round in shape.

Parts of a Diamond, What Those Angles Are Called

The flat top of a diamond is called the table. The thin center perimeter of the stone is the girdle. The section between the table and the girdle is called the crown.

The section between the girdle and culet (the point at the bottom) is called the pavilion.

All the flat planes on a diamond are called facets. The table is largest facet. The culet is the smallest.

Depending on how the stone is cut, round diamonds will have different numbers of facets.

In a good diamond, all the facets are completely smooth and polished.

Dimensions: Do I Have to Understand This Stuff? (Yeah)

All the different dimensions of diamonds are measured in millimeters. These measurements would include diameter, width, and height. These measurements and the angles and the ratios of the different parts of a diamond to each other are what are called proportion.

All other C’s being equal, a stone cut with ideal proportions or near ideal will shine and stand out more than a poorly cut one.

Ideal Cut: Do I Have to Buy an Ideal Cut?

Experts often refer to “ideal” cut diamonds. These are stones deemed to have been cut using agreed upon proportions to maximize their shine and sparkle.

You’re probably wondering why all diamonds aren’t cut “ideally?” Oftentimes, it’s just not possible due to what the diamond cutter has to work with.

The rough stone might not present enough material to allow for an ideal cut. There could be a pretty big carbon spot that needs to be cut away.

There are plenty of gorgeous diamonds that are near ideal cuts that look fabulous. You do not have to have an ideal cut or one of the labeled diamond cuts like the Tolkowski cut or Hearts and Arrows or other patented cut styles to have a lively and sparkly diamond. But it helps to have one of these great cut styles.

Why Would Someone Cut a Diamond Badly?

Another reason for poorly cut diamonds is due to diamond cutters wanting/needing to preserve as much stone weight as possible for the maximum final diamond weight.

As an example, a particular diamond might weigh .90 carats if it was cut ideally. Diamonds weighing 1 carat or more fetch a more premium price. The cutter might be tempted / or told to, facet the diamond a bit differently to preserve the extra weight, making it a more expensive diamond by weight.

Reflection, Refraction, Dispersion, Words You Need to Understand

Light bouncing off the surface of a diamond is called reflection.

Light entering the stone and bouncing off an interior wall is called refraction.

The light exiting the diamond is called dispersion. As you might have guessed the more light refracting from inside the diamond and dispersing from the table, the better.

Good diamonds refract and disperse lots of light. Bad diamonds don’t. They just reflect light, which any piece of clean piece of glass can do.

You need to look beyond mere reflection. The reason good refraction and dispersion are so important in your chosen diamond is because when you wear your diamond every day it will get dirty.

A well cut diamond will continue to sparkle with less light coming in. A bad diamond when it gets dirty will sit there like a piece of dull glass. A bad diamond might work OK in a pendant that stays relatively clean, but your ring diamond will get lotion, soap scum and just life dirt on it.

If it’s a good diamond, it’ll keep that love sparkle going. If it’s a bad diamond it’ll break your heart.

When you look at a diamond, rock it back and forth to see the light dispersion. The most important light dispersion is what you can see looking down into the table. You’ll also see dispersion of light from those top crown facets.

Once you can tell the difference between light reflection and light refraction, you will be ahead of most first time diamond shoppers.

Fancy Display Lights Can Fool Your Eye When Diamond Shopping

Poorer quality diamonds can be made to look better than they really are by showing them under the mega-wattage overhead lights of some jewelry stores.

A diamond of  poor quality will not look as good at your office or in your kitchen as it did at the store where you bought it.

For this reason, I recommend examining diamonds in natural light, away from the jewelry store counter brilliance.

Find the Ugly Light to Find Your Good Diamond

Don’t let fancy light and a clean reflection fool your eye. When you are shopping for your diamond, try to look at it away from  the mega-wattage overhead lights of the jewelry store.

Fancy high intensity display light can make the poorest cut diamond refract light like a champion. Take that diamond that you are considering to a more poorly lit part of the room, or a hall, or even the bathroom.

Compare a diamond that has proven nice light refraction next to a candidate diamond. This would be a diamond that you know is awesome, like in a friend's engagement ring.

Once you are in the ugly light, only a well cut diamond will still give good light dispersion.

How is a Bad Cut Diamond Made?

Most of the time a bad diamond-cut result has to do with the choices the diamond cutter made. He may have had the bad luck of being saddled with big carbon inclusions that were naturally occurring in all the wrong places in the rough diamond crystal. The cutter took the hand he was dealt and made his choices and they didn’t include what would create the most light dispersion.

How You Can Spot a Bad Diamond Cut

A shallow cut diamond may look bigger due to a larger table, but due to all the light escaping out the sides, it lacks the brilliance and fire of a smaller well cut diamond.

Deep cut diamonds often suffer the same fate. They don’t refract light up toward the eye the way a more ideal cut diamond does.

The angles, symmetry, and facets of an ideal cut diamond or near ideal have been skillfully and effectively proportioned to reflect and refract the maximum amount of light. An well cut diamond shines and sparkles and shows fire and brilliance. Poorly cut diamonds don’t.

How to Tell a Well Cut Diamond from a Poorly Cut Diamond

If you’re like John, all the facts, figures, and dimensions on a GIA certificate won’t mean squat to you. I don’t even know what all the ratios and dimensions mean off the top of my head!

So what do we do? Assuming two diamonds are the same weight, the same color, and of the same clarity, how do we tell which is better cut? What’s a poor woman (or guy) to do?

Start by examining the two diamonds side by side. Look at them from as many different angles as you can.

Do this with your eye as well as with a loupe. Look straight down through the table. (The flat part on top)

Four Steps to Checking for Good Diamond Cut

1. Look at each stone from the side. Look for imperfections, scratches, and chips.

2. Pay attention to the symmetry of the facets. Are they all the same shape the same size or does one look slightly out of proportion to the others?

3. Check the girdle. Make sure it’s perfect all the way around.

4. Check the culet. Make sure it’s not chipped or broken. (Bottom pointy part)

Dispersion, Sparkle and Pizazz – Does That Diamond Sing?

Finally—and this is most important!—examine the diamond for its natural sparkle! See if one stone shows more color reflection than the other.

Does it seem to have just a little more pizzazz? If it does, chances are it’s a better cut stone.

I care little for anything else. Oh yeah, except color and clarity, but that’s another post! Is the rock I’m looking at a little ball of blazing sunlight or a dull lump of beach glass? I call this the Pizzazz Factor!

A diamond with pizzazz, a good diamond, will sparkle, shine, glitter and glow in cleanliness and dirtiness. (I mean we have lives and are busy and can’t be expected to slavishly clean our diamond ring nightly!) A poorly cut, or bad diamond will break your heart. Or your wallet as John can tell you.

Put Down the Loupe, Use Your Eyes

Three Ring Wedding Set with Inherited Diamonds

Look at How This Diamond Returns Light and it's in Shadow!

You don’t have a loupe with you in life. How will your diamond look in life, in normal everyday places? In ugly light? Use your naked eye to see the light dispersion from one candidate diamond to another. Let your eye make the final choice.

The diamond you are considering may have great color, and fabulous clarity and a fantastic price, but if the way the stone has been cut is flawed then you’re looking at a bad diamond.

John and Marly's Excellent Ending

Just so you know John and Marly had a happy ending. They returned their diamond less a restocking fee, which John was happy to pay. They looked at diamonds side by side with me and picked a diamond with a lot of light refraction and dispersion.

The Vaseline Test

We even did the Vaseline test. I rubbed Vaseline on the bottom of each diamond to simulate the life dirt that gets on your diamond.

One diamond sparkled more energetically than the other after the test and it is now on Marly’s hand. She love, love, loves it. In her words. May the diamond you select make your heart and her heart sing!

Calla Gold

A book I recommend is:

DIAMONDS, 3RD EDITION The Antoinette Matlins Buying Guide—How to Select, Buy, Care for & Enjoy Diamonds with Confidence and Knowledge

Antoinette Matlins Excellent Book, "Diamonds" if you Want to Know Everything!

Antoinette Matlins Excellent Book, "Diamonds" if you Want to Know Everything!

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About Calla Gold

Calla Gold is a Personal Jeweler and Author who takes pride in working with clients one-on-one to integrate their personal sense of style and taste into custom designed jewelry and repaired jewelry pieces.   Unlike typical Santa Barbara jewelry businesses, Calla Gold has no brick-and-mortar location. Calla Gold comes to you, bringing you the jewelry collection you want to see and collaborating with you to create unique custom jewelry. Calla also works with at-a-distance clients.

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9 years ago

This was absolutely eye opening about bad diamonds. Most of the points mentioned on this blog post I had never even heard of!
This information is absolutely essential for anyone looking into buying a diamond. Great post!


Mark Johnson
9 years ago

Hi Calla,

Another wonderful post. It was great to read your post and such a detailed account of diamond cut – so often overlooked by both buyers and sellers. It is astounding to think that a diamond with the same weight, colour and clarity can vary by as much as 40% in value, depending on the cut. There are so many great points to take away here!


8 years ago

Thanks for an interesting read! Curiously, many contemporary jewellers are now looking for more ‘flawed’ gems – which fall down on the traditional measures of clarity or colour and even on cut and making interesting and eye catching pieces with them – I’m thinking of the Polly Waleses and Ruth Tomlinsons of this world. After all, a preference for super clear diamonds, or a lot of fire, or no spotting, might be a cultural trend some are willing to buck (much like the number of brides opting for something other than white wedding dresses). Sometimes a ‘compromise’ on colour, for… Read more »

Veronica Lilliana
Veronica Lilliana
8 years ago

I must say, thank you for going into such detail about this topic. It only confirms that my fiancé did his homework and pretty much mentioned all these points to me when he explained his adventure in finding the perfect diamond for my engagement ring. My round solitaire sparkles so much, especially under dim lighting. He didn’t splurge on carat weight or clarity or color. He took it into account yes, but made sure the CUT was as close to ideal as possible. You can barely tell if a diamond is colorless and has no inclusions. It’s the cut that… Read more »

Bob Moore
Bob Moore
5 years ago

I am concerned about a jeweler switching out a good diamond for a bad one when you
take your ring in for cleaning or resetting. How can we be sure we are being treated fairly.

Sariah Meagle
Sariah Meagle
5 years ago

Wow, I didn’t know that a good diamond should have completely smooth and polished facets. I suppose it would help if the cut style from a diamond cutter would be ideal since it would bring out the shine of the diamond. Since I want to have a diamond that will refract light, I will be sure to buy from a good cutter so that I can get the best value for my investment.

Sarah Smith
Sarah Smith
5 years ago

I really appreciate your advice that a quality diamond will have an intact culet and symmetrical facets. This will be really helpful when my husband and I look for rings for our 20th anniversary. We’ll make sure to check these areas of a diamond before investing in a set of rings.

Callum Palmer
Callum Palmer
4 years ago

I’m looking ot buy a diamond. I’d want it to have a good cut. Doing more research on this should help me find the right one.

Om Agarwal
Om Agarwal
4 years ago

This blog change my perception about diamonds and I don’t aware of these facts about diamonds. Thanks for the sharing such a informative blog post this help to improve my knowledge about diamonds. I am a diamond lover and love to read about diamonds. I am running a business of diamonds and gemstone manufacturing.

ideal cut diamond
ideal cut diamond
4 years ago

Ideal Cutting is simply the most beautiful way to cut a diamond.