Diamonds
The 4Cs, and which one actually deserves your money
A working jeweller's guide to reading a diamond report — which of the 4Cs the eye can see, and which you can trade down without anyone noticing.
Most people walk into a jewellery shop asking for a colourless diamond. That is one of the 4Cs, and honestly it is not the one that decides whether the stone looks alive on a hand.
The 4Cs are Cut, Colour, Clarity and Carat. All four move the price. They do not all move how beautiful the stone looks, which is where the money gets wasted.
Cut is the one you never compromise on
Cut does not mean shape. It means how well the stone was proportioned and finished — whether the angles send light back out through the top.
A diamond is a set of mirrors. Cut too shallow and light escapes through the bottom. Too deep and it leaks out the side. Either way you get a stone that looks dull no matter how white and clean the report says it is.
GIA grades cut as Excellent, Very Good, Good, Fair and Poor. Buy Excellent or Very Good, nothing below. The price gap between Excellent and Good is roughly 10-15%. The visual gap is enormous.
If the budget is tight, drop colour or clarity. Never drop cut.
Colour: G-H is where the value sits
Colour runs from D, completely colourless, down to Z, visibly yellow. Prices step up sharply between grades, but the eye cannot separate D from G unless the two stones are lying next to each other on a white card.
| Grade | Visible to the eye | Best for |
|---|---|---|
| D-F | No difference | Buyers who want the top grade and are not budget-limited |
| G-H | Invisible unless compared | The value sweet spot, our usual recommendation |
| I-J | Slightly warm | Excellent in yellow gold or rose gold settings |
| K and below | Clearly yellow | Not recommended for a solitaire |
Here is the part shops rarely mention: in a yellow gold or rose gold setting, the metal reflects warmth into the stone anyway. Paying for D-F there buys you almost nothing. Take I-J and put the difference into cut or size.
Clarity: stop at eye-clean
Clarity measures inclusions under 10x magnification, from FL and IF through VVS, VS, SI and down to I1-I3.
The term that matters is eye-clean — no inclusions visible to the naked eye at normal viewing distance. That usually starts at VS2, and plenty of round brilliants are still eye-clean at SI1.
The price gap between VVS1 and VS2 can reach 25-30% for a difference nobody will ever see on a finger, unless they carry a loupe to dinner.
One warning: always inspect an SI2 in person or ask for magnified photos. Some have an inclusion sitting right under the table, which does show.
Carat: buy just under the round number
A carat is 0.2 grams. Price does not rise smoothly with weight — it jumps at the round numbers, because that is what people ask for.
A 1.00 ct stone costs 15-20% more than a 0.95 ct. The difference in face-up diameter is under half a millimetre. Nobody sees it. The jump points are 0.50, 0.70, 0.90, 1.00, 1.50 and 2.00 carats.
Buy 0.90-0.98 instead of 1.00 and spend the difference on cut. That is the single most useful thing we tell clients.
About the report
Any diamond from 0.30 ct should come with a report from an independent laboratory. GIA is the international reference. In Thailand, GIT is the government institute and is equally rigorous.
Every report carries a number you can verify free on the laboratory's own website. Be careful with any shop offering its own in-house certificate — nobody outside that shop can check it.
Are lab-grown diamonds real diamonds
Chemically and optically they are identical, and no loupe or naked eye can tell them apart — it takes specialised equipment. They cost roughly 60-80% less and hold far less resale value. A GIA report always states clearly when a stone is laboratory-grown.
What should I buy with a budget of about 3,000 USD
At that level we would suggest around 0.50-0.60 ct, Excellent cut, G-H colour, VS2 clarity, set in 18K white gold. That gives you a lively, eye-clean stone rather than a larger one with a mediocre cut.
Does fluorescence matter
In most stones it makes no visible difference, and medium blue fluorescence can even offset slight warmth in I-J colour grades. Very strong fluorescence in a D-F stone can occasionally cause a milky look, so inspect those in person.