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Education›Lab Grown Diamond Guidance›Diamond Cut Guide

Lab Grown Diamond GuidanceFenora Guide10 min read

Diamond cut guide.

Cut is the most important of the 4Cs — and the most misunderstood. It does not mean the shape of the diamond. It means the quality of the faceting and how precisely the diamond has been proportioned to maximise the return of light. This guide explains everything: what cut actually measures, how it creates brilliance and fire, how to read the cut grade on an IGI certificate, and why you should never compromise on it.

Cut — the most important C

Cut is the most important of the 4Cs. It is also the most misunderstood. Cut does not refer to the shape of the diamond — round, oval, pear, emerald. Cut refers to the quality of the faceting: how precisely and proportionally a rough diamond has been cut so that light enters, reflects internally and exits through the top of the stone in a perfect display of brilliance and fire.

A poorly cut diamond will look dull and lifeless regardless of how large it is, how high its colour grade is or how clean its clarity. An Excellent cut diamond with a G colour and VS2 clarity will outperform a poorly cut diamond with a D colour and VVS1 clarity in every visual way that actually matters when the ring is worn.

Cut is the one C where there is a correct answer. For colour, clarity and carat weight, the right choice depends on budget and preferences. For cut: always choose Excellent or Ideal. Never compromise on cut to get more size, better colour or better clarity. A bigger, poorly-cut stone looks worse than a smaller, beautifully-cut stone.

“Every time a client asks me to compromise on cut, I ask them to look at two stones side by side — the same carat, one Excellent cut, one Good cut. After that, no one ever compromises on cut again.”
— Yash Chandpara, Founder

How cut creates brilliance, fire and scintillation

Diamond cut quality is measured by how effectively a stone interacts with light. Three distinct optical phenomena create the visual character of a well-cut diamond — and understanding each one explains why cut quality affects appearance so profoundly.

The three optical properties of a cut diamond

Brilliance — white light reflected back from the interior of the diamond through the top facets. This is the overall brightness and luminosity of the stone. An Excellent cut diamond returns nearly all white light back through the table; a Good cut loses significant light through the pavilion and sides
Fire — the dispersion of white light into spectral colours — red, orange, yellow, green, blue, violet. Created by the crown facets splitting light as it exits the stone. A well-cut diamond with ideal crown angles creates vivid flashes of colour visible in normal lighting
Scintillation — the pattern of light and dark areas and the sparkle that appears when the diamond, the light source or the observer moves. The alternating flash of brilliance that makes a diamond appear alive rather than static

All three properties are directly determined by the proportions and angles of the cut. Change the crown angle by just a few degrees and the balance between brilliance and fire shifts. Change the pavilion depth and light return drops dramatically. The precision of diamond cutting at the Excellent grade is extraordinary — and the visual result is equally extraordinary.

The anatomy of a diamond cut

Understanding the components of a diamond cut — and what role each plays in light performance — makes it much easier to understand what an IGI certificate is telling you about a specific stone.

Key cut proportions on an IGI certificate

Table % — the width of the table facet as a percentage of the total diameter. Ideal range: 54–58% for round brilliants
Depth % — the total depth of the stone as a percentage of its diameter. Ideal range: 59–62.5% for round brilliants
Crown angle — the angle of the crown facets relative to the girdle plane. Ideal: 34–35°. Affects fire and brilliance balance
Pavilion angle — the angle of the pavilion facets. The single most critical number in cut quality. Ideal: 40.6–41°. Small deviations cause significant light loss
Culet — the tiny facet at the very bottom tip of the stone. Should be None or Pointed. A large culet creates a visible dark circle in the stone

Cut grades — understanding the IGI scale

IGI grades diamond cut on a scale from Excellent (the highest) to Poor. For engagement ring centre stones, only Excellent and Very Good are worth considering — and Excellent should always be the target.

Excellent

The finest cut grade

Proportions, symmetry and polish are at the highest level achievable. Light enters the stone and returns through the top in a perfectly balanced display of brilliance and fire. Every facet performs exactly as designed. The Fenora standard for all stones.

Fenora Recommended

Very Good

One step below Excellent

Proportions and symmetry that produce nearly identical light performance to Excellent in most viewing conditions. A very small reduction in light return that is essentially invisible in everyday wear. An acceptable choice where budget is a significant factor.

Acceptable

Good

Noticeably different in performance

Light leaks from the sides or bottom of the stone. The diamond will look noticeably less brilliant than an Excellent or Very Good cut. Fenora does not recommend this grade for engagement ring centre stones.

Not Recommended

The visual difference between Excellent and Very Good is small in most conditions. The visual difference between Excellent and Good is immediately apparent to any observer. The Fenora standard is Excellent for all stones. Every diamond in the Fenora collection is Excellent cut.

“Cut is the one thing I will never compromise on. A smaller Excellent-cut stone always looks better than a larger Good-cut stone. Always. There is no exception to this rule.”
— Yash Chandpara, Founder

Cut and diamond shape

Cut grade is applied differently to different diamond shapes. For round brilliants, IGI provides a specific cut grade because the ideal proportions for a round brilliant are precisely defined and universally agreed upon. For fancy shapes (oval, pear, emerald, cushion etc.), IGI grades cut more broadly — as polish and symmetry rather than a single cut grade.

Cut by diamond shape

Round brilliant — the only shape with a standardised cut grade on the IGI certificate. Always choose Excellent cut for a round brilliant. No exceptions
Oval — no standardised cut grade. Judge cut quality by the visual result: is the stone bright and evenly illuminated? Check for bow-tie effect (a dark shadow across the centre) — always view in video
Pear — similar to oval. No standardised cut grade. Check for the bow-tie effect and uneven brilliance. View in video before purchasing
Emerald and Asscher — step-cut shapes. Light performance is different from brilliant cuts — the mirror-like depth is the goal, not maximum brilliance. Excellent symmetry and polish are essential
Cushion — multiple cutting styles exist for cushions, each producing a different light pattern. Always view in video or photograph before purchasing
Princess — no standardised IGI cut grade. Check for even, bright illumination across the entire stone surface in video

Cut mistakes to avoid

Choosing Good cut to save budget for more carat weight — a bigger, dull stone is worse than a smaller brilliant one
Ignoring the pavilion angle on a round brilliant because other grades look good — pavilion angle is the most important single number
Purchasing an oval or pear without viewing it in video — bow-tie effect only reveals itself in motion

Cut quality and budget

The most common question about cut quality and budget is: if I am choosing between a 1.0ct Excellent cut stone and a 1.2ct Very Good cut stone at the same price, which should I choose?

The answer is always the 1.0ct Excellent cut. Here is why: the Excellent cut stone will be visibly more brilliant, show more fire and appear more alive in all lighting conditions. The additional 0.2ct in the Very Good stone will not make it look larger enough to compensate for the reduction in sparkle. On the hand, the Excellent cut stone will draw more attention and more admiration.

If the budget forces a trade-off between...	Choose this	Because...
Excellent cut vs more carat weight	Excellent cut always	A brilliant smaller stone looks better than a dull larger one
Excellent cut vs better colour grade	Excellent cut always	Cut affects appearance more directly than colour in a ring setting
Excellent cut vs better clarity grade	Excellent cut always	A VS2 Excellent cut looks better than a VVS1 Good cut in every real-world condition
Very Good vs Excellent at identical quality	Excellent always	The price difference between Very Good and Excellent at the same colour and clarity is typically small. It is worth it
Excellent cut at slightly lower carat	Always worth it	0.9ct Excellent cut vs 1.0ct Very Good — choose the 0.9ct. It will look better in every light condition

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See cut grades side by side.

Book a free online consultation with Yash Chandpara. He will show you Excellent and Very Good cut stones side by side on screen — so you can see the real difference before deciding.

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