Buying guidesFirst purchase8 min read

A first diamond, on a set budget

A fixed budget is not a constraint on buying well — it is the thing that makes buying well possible, because it forces every grade to justify itself. This is the method we would use with our own money.

Decide three numbers first

Before looking at a single stone, fix three things: the most you will spend, the smallest size you would be happy with, and the date you need it by. Every subsequent decision is a trade between those three, and if they are not written down the budget drifts upward one small step at a time.

Be realistic about the size figure in millimetres rather than carats. A 1.00 ct round is about 6.5 mm across; a 0.90 ct is about 6.3 mm. If what you actually want is a stone that reads as substantial on a hand, the millimetre figure is the honest target and the carat figure is a proxy for it.

The date matters more than people expect. Sourcing a specific stone to a specification takes time, and buying under deadline pressure is how you end up paying retail for whatever happens to be in the case.

The order to spend in

Spend on cut until it is excellent, spend on clarity until the stone is clean to the eye, spend on colour until it looks white in the metal you have chosen, and put everything left into size. In that order, every time.

The reason is that only one of the four Cs changes how much light the stone gives back, and that is cut. A dull diamond with a flawless clarity grade is a dull diamond. Meanwhile clarity and colour both have a threshold past which additional spending buys something genuinely invisible, and the entire craft of buying well is finding that threshold and stopping there.

Size is last not because it does not matter — it is usually what the wearer notices first — but because it is the most expensive per unit of visible difference, and because cut quality partly substitutes for it. A well-cut stone faces up larger and brighter than a heavier one cut for weight.

Where first-time buyers overspend

Four places, consistently. Clarity above eye-clean is the largest: the scale is defined at 10× magnification, so grades above VS are paying for something that requires equipment to see. Colour above G in white metal, or above H in yellow, is the second.

The third is landing exactly on a round carat weight. The fourth is the premium attached to a name rather than to the stone — branded cuts and house grading systems that cannot be compared with anything else. A stone with an independent GIA or IGI report can be compared with every other stone in the world; one with a proprietary grade cannot.

There is a fifth, subtler one: buying a stone that grades well but was never seen. Milkiness from dense clouds or internal graining does not always appear on the plot, sometimes only as a comment. Ask for a video before committing to any stone bought remotely.

Clarity above eye-clean: Graded at 10×. Above VS you are buying loupe performance.
Colour above the metal's needs: G in white, H in yellow. Beyond that the setting hides the difference.
Exactly on a magic size: Cross the step and the per-carat rate rises for every carat, not just the last point.
Proprietary grading: A house grade cannot be compared with anything. Insist on GIA or IGI.
Never seeing the stone: Milkiness and bow-ties are not graded. Ask for a video, and for an ASET where it exists.

How to compare two quotes properly

Convert both to a price per carat. That is how the trade quotes, and it is the only way to compare stones of different weights on the same basis — a 1.20 ct at one rate and a 1.05 ct at another are not comparable until you divide.

Then check that you are comparing like with like. Same laboratory, because grading is not perfectly interchangeable across laboratories. Same shape and similar proportions. Same fluorescence. And check the measurements, not just the weight — two 1.00 ct stones can differ by a third of a millimetre across, which is a visible difference you would otherwise pay for blindly.

Finally, ask both sellers the same three questions: is it eye-clean, is there a video, and what is the girdle thickness. The answers, and how readily they come, will tell you a good deal about who you are dealing with.

A first stone, specified

Built for maximum visible quality per pound. Every line is a threshold rather than a maximum — reach it, then stop.

Origin: Lab-grown, if size is the priority; The same budget reaches a larger or higher-graded stone. Note that our lab-grown white stock runs D–F, so there the colour line moves up rather than the price coming down.
Shape: Round, or an elongated fancy for more spread; Round is the easiest to buy well remotely. Oval and pear face up larger per carat.
Cut: Excellent or Ideal; Never the line to economise on. It is the only C that changes light return.
Clarity: SI1, confirmed eye-clean; VS2 if you cannot see the stone or a video first. Step cuts higher again.
Colour: H – J; In yellow or rose gold, J is comfortable. In platinum, work up to G or H.
Carat: 0.90, 1.40, 1.90; Just under each step. Check the millimetres — that is what shows.
Fluorescence: Faint to Medium blue; In an I or J it can help the colour, and it usually costs less. Judge in daylight.
Report: IGI or GIA — never a house grade; An independent report is what makes comparison across sellers possible at all.

See natural stones in this range Send this specification to the desk

Terms used in this guide

The short version. Each one is defined in full, with what a report prints for it, in the glossary.

Eye-clean: No inclusion visible to an unaided eye at normal viewing distance.
Price per carat: How the trade quotes diamonds: a rate per carat, multiplied by weight for the total.
Magic sizes: The round weights — 0.50, 0.75, 1.00, 1.50, 2.00 ct — where price steps up sharply.
Spread: How large a stone looks from above, relative to what its carat weight would suggest.
Milky: A diamond that looks faintly cloudy or sleepy rather than crisp and transparent.
Cut grade: An overall verdict on how well a round brilliant has been cut — issued for rounds only.
Measurements: The stone's physical size in millimetres: length × width × depth.
Lab-grown: A real diamond grown in a reactor rather than in the earth — chemically and optically identical to a mined one.

Frequently Asked Questions

What buyers ask us most often about this particular purchase.

What is the cheapest way to get a diamond that looks big?

Three levers, in order. Buy lab-grown, where the same budget reaches a larger stone. Choose an elongated shape — oval, pear or marquise — which faces up larger than a round of the same weight. And buy just under a magic size. Keep the cut grade high throughout: a well-cut stone looks larger than a deep one of the same weight.

Is SI1 clarity a mistake?

Not at all, provided you confirm the specific stone is eye-clean. SI1 is where a great deal of the best value in the market sits. The caveat is that the grade alone does not guarantee it — the position and colour of the inclusion decide, so read the plot or ask us to check.

How much does cut actually change the price?

Enough to notice, and it is the one place we would pay it without hesitation. An Excellent cut commands a premium because it shows the stone's other qualities at their best — the colour you paid for looks whiter and the weight you paid for faces up in full. Very Good is a legitimate saving; below Good, the saving rarely covers the light lost.

Can I trust grades from a smaller laboratory?

Grading is expert opinion, and consistency varies between laboratories. GIA and IGI are the two we work with, and the practical rule is never to compare a stone graded by one laboratory with a stone graded by another on grades alone. A stone with a report from neither is very hard to value.