TL;DR — What actually matters

The 4Cs are Cut, Colour, Clarity, and Carat. Cut matters most because it controls how the diamond reflects light, and most buyers in Montréal underspend on it. Colour and clarity have wide ranges where the difference is invisible to the naked eye — pay for what you can see, not what looks good on paper. Carat is just weight, not size, and small jumps in carat trigger big jumps in price. A well-cut 0,90 ct G VS2 often outperforms a sleepy 1,00 ct F VS1 in real life, for less money.

Table of contents

• What the 4Cs actually are
• Cut: the only C that creates sparkle
• Colour: D–Z explained without the snobbery
• Clarity: VS1 and SI1 are usually invisible
• Carat: weight, not size
• How we tell you the truth at the counter
• FAQ

What the 4Cs actually are

The 4Cs are the grading framework the GIA introduced in the 1950s. Cut grades how well a diamond is shaped and polished. Colour grades how white (or yellow) it is. Clarity grades the internal inclusions. Carat is the weight — 1 carat equals 0,2 grams.

Every reputable lab — GIA, IGI, AGS — uses the same letters and numbers. So far, so neutral. The marketing problem starts when retailers push you toward the grades with the biggest markup instead of the grades you can actually see. That is the gap this article closes.

We are in Montréal. We grade, set, and resell diamonds every week at Bijouterie Jamil. What follows is what we tell our own family when they ask.

Cut: the only C that creates sparkle

Cut is the most important of the 4Cs and the most overlooked. Colour, clarity, and carat are about the rough stone you started with. Cut is about the human work — the proportions, angles, polish, and symmetry the cutter chose. A poorly cut D Flawless diamond looks dull. A well-cut J SI1 looks alive.

On a GIA report, Cut grade only applies to round brilliants: Excellent, Very Good, Good, Fair, Poor. For round brilliants, do not go below Excellent unless you have a very specific reason. The price gap between Very Good and Excellent is small. The visual gap is large.

For fancy shapes — oval, pear, emerald, cushion — GIA does not issue an overall cut grade. You judge cut by looking at the polish and symmetry grades, the length-to-width ratio, and most importantly, by holding the stone in your hand under normal indoor light. We do this for clients in our Montréal showroom every day. A bad oval has a "bowtie" — a dark band across the centre. A good oval doesn't.

The Quebec context: most apartments and restaurants here are lit warmly — incandescent or warm LED. A well-cut diamond performs in that light. A poorly cut one disappears. Pay for cut.

Colour: D–Z explained without the snobbery

GIA grades colour from D (completely colourless) to Z (light yellow). Anything past Z is a "fancy yellow" and graded on a different scale. The grading is done face-down under controlled lighting against master stones. It is not how the diamond looks face-up on your finger.

Here is the honest breakdown:

• D, E, F — Colourless. D is the top. Most people cannot tell D from F when the stone is set. F costs noticeably less. F is a smart ceiling.
• G, H, I, J — Near colourless. G and H face up white in almost any setting. I and J start to show a faint warmth in white gold or platinum but vanish in yellow gold or rose gold.
• K and below — Faint yellow. Visible to most eyes face-up. Use only with a warm metal or for an antique look.

The market overpays for D, E, F. The smart buy for most engagement rings is G or H in platinum/white gold, or I/J in yellow or rose gold. You will save 20–35 % versus a D-colour stone of the same cut, clarity, and carat — money that goes much further into a better cut grade or a slightly larger size.

Clarity: VS1 and SI1 are usually invisible

Clarity grades the internal flaws (inclusions) and surface marks (blemishes). The scale, top to bottom: FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, I3.

The phrase that matters: eye-clean. An eye-clean diamond shows no inclusions to the naked eye at normal viewing distance — about 25–30 cm. Most VS1 and VS2 stones are eye-clean across all shapes. Many SI1 stones are eye-clean too, especially in round brilliants where the facets hide inclusions. SI2 is a coin flip — sometimes eye-clean, sometimes not, and we always check the GIA plot diagram and the stone itself before we recommend one.

What you are paying for above VS2 is something only a 10x loupe can see. That is not a flaw worth $2 000 CAD to fix. We would rather put that money into cut.

One exception: emerald cuts and Asscher cuts. Their long, open facets ("step cuts") hide nothing. For step cuts, stick to VS2 or better. For round, oval, cushion, princess — SI1 eye-clean is a great value.

Carat: weight, not size

Carat is mass. 1 carat = 0,2 grams = 200 milligrams. It does not directly tell you how big the diamond looks face-up. Two 1-carat rounds can look noticeably different in diameter depending on how deep they are cut. A well-cut 1 ct round is roughly 6,4 mm across the top. A deep, poorly cut 1 ct can be 6,1 mm — smaller-looking and duller.

Carat prices jump at psychological thresholds: 0,50 ct, 0,70 ct, 0,90 ct, 1,00 ct, 1,50 ct, 2,00 ct. The jump from 0,90 to 1,00 ct can be 15–25 % more money for less than a millimetre of difference. A 0,90 ct G VS2 Excellent cut runs roughly $4 500–$6 500 CAD natural, vs. a 1,00 ct of the same specs at $5 800–$8 500 CAD. Same finger appearance. Real money saved.

Our standing advice in the showroom: shop just under the round numbers. 0,90, 1,40, 1,90. You get the look without the weight tax.

How we tell you the truth at the counter

When you walk into Bijouterie Jamil with a budget — say $5 000 CAD for an engagement ring — we do not start by asking for the highest grades you can afford. We ask three questions: What metal is the band? What does her current jewellery look like? Where will she wear this most?

Then we build the stone backwards. Pick the cut grade first (Excellent for round, hand-selected for fancy). Pick the largest carat that fits the budget. Choose colour to match the metal. Choose clarity to be eye-clean, not loupe-clean. We pull three or four stones from our safe and you compare them under daylight, warm light, and a loupe — in that order.

For clients who cannot visit in person, we send HD video and macro photos of any stone before purchase. That request is free and standard — we do it dozens of times a month. Just ask.

You can also compare two stones side by side at the bench, with our master jeweller walking you through what you are seeing in plain language. That is what "expert next door" actually means.

For more on choosing the ring around the stone, see our guide on how to choose an engagement ring. For lab-grown vs. natural cost differences at the same 4C grade, see lab-grown vs. natural diamonds. For what those GIA and IGI reports actually certify, see diamond certification explained. And if you are choosing the metal for the band, our gold karats guide covers 10K, 14K, and 18K tradeoffs.

FAQ

Which of the 4Cs matters most? Cut. It controls how the diamond reflects light, and a great cut makes a smaller or lower-grade stone outperform a larger, higher-graded but poorly cut one. For round brilliants, never go below GIA Excellent.

Can I see the difference between VS1 and SI1 with the naked eye? Usually no. Both are typically eye-clean in round, oval, cushion, and princess shapes. SI1 saves you 15–30 % over VS1. The exception is step cuts (emerald, Asscher) — stick to VS2 or higher there.

Is a D-colour diamond worth the price? For most buyers, no. D, E, and F look identical to the naked eye once set. G or H in white metals, or I/J in yellow or rose gold, gives you the same face-up look for 20–35 % less.

How much does a 1-carat diamond cost in Montréal in 2026? A natural 1 ct round, GIA Excellent cut, G colour, VS2 clarity, runs roughly $5 800–$8 500 CAD at Bijouterie Jamil depending on exact specs. Lab-grown of the same grade runs roughly $1 800–$3 000 CAD. Both come with full lab reports.

Why does going from 0,90 ct to 1,00 ct cost so much more? Psychological price thresholds. Cutters and dealers price-jump at round numbers because demand spikes there. A 0,90 ct can be 15–25 % cheaper than a 1,00 ct of the same quality, with less than a millimetre of visible difference. Shop just under round numbers.

Do you grade diamonds in-house at Bijouterie Jamil? We verify and inspect every stone in our Montréal workshop, but for any diamond over 0,30 ct we sell with an independent lab report from GIA, IGI, or AGS. We do not self-certify. If a stone you are considering elsewhere has no lab report, we can appraise it for you — bring it in.

Can I get more photos or a video of a specific stone? Yes. We send HD macro photos and short videos of any loose stone before purchase, free. Email us the GIA report number or the product link and we will turn it around within one business day.

What about fluorescence — is that part of the 4Cs? No, it is a separate grade on the report. Faint or medium blue fluorescence is usually neutral or slightly positive (it can make a J-colour stone look whiter in daylight). Strong fluorescence in colourless grades can occasionally cause a milky look — we always check before recommending. Ask us if you see "Strong" on a report.

Visit us in Montréal

If you want to see two or three stones side by side and hear the tradeoffs in plain language, visit our showroom in Montréal or book a private appointment. We will pull stones to your budget and walk you through the differences yourself — no pressure, no upsell. You can also email a GIA report number and we will tell you honestly whether that stone is priced fairly.

Book a consultation · Visit the showroom · Request photos of a specific diamond

About the author Nader Khazzoum is co-owner and master jeweller at Bijouterie Jamil in Montréal. He specializes in custom fabrication, stone setting, and laser welding, and has been grading and setting diamonds at the family bench for over 20 years.