Why do antique diamonds not get a cut grade?

Laboratory cut grades are calculated only for standard round brilliants, using proportions defined by modern ideals. Old mine cuts, old European cuts and fancy shapes fall outside that system, so the field is left blank or marked not applicable. A missing cut grade is not a criticism of the stone.

Is fluorescence bad in an antique diamond?

Usually not, and it can be an advantage. Blue fluorescence can make a faintly warm stone appear whiter in daylight. Strong fluorescence occasionally causes a hazy look in a small proportion of stones, so view any strongly fluorescent diamond in sunlight before buying. Fluorescent stones typically trade at a discount, which makes them good value for antique cuts where warmth is acceptable anyway.

What is the most important measurement on a report for an antique stone?

The millimetre dimensions. They tell you how large the stone looks face-up, which carat weight alone does not, because antique cuts carry more weight below the girdle than modern stones.

Does a report prove a diamond is antique?

No. A report describes the stone as it is now. It may identify the cutting style, which is strong evidence of era, but it cannot tell you whether the stone is original to its setting or whether it has been recut from an older shape.

Should I insist on a report before buying an antique diamond?

For a significant purchase, yes, or at minimum a return window long enough to obtain one. For small accent stones in a period setting it is neither practical nor expected, since the stones would have to be removed.

September 23, 2026

How to Read a Diamond Report on an Antique Stone

By Sasha Tarasova

Filed under Antique Diamonds & Diamond Cuts Buying Guides

Loose old mine and old European cut diamonds on green velvet with brass calipers, a loupe and diamond cut diagrams.

Short answer: a grading report describes a diamond accurately, but its structure was designed for modern round brilliants. On an antique stone, the cut grade is either absent or misleading, and the fields that actually matter are the measurements, the colour, the clarity plot and the comments. There are also four important things no report will ever tell you — and they are usually the ones that determine what you should pay.

Read the measurements before anything else

The millimetre dimensions are the single most useful line on the report for an antique stone, and most buyers skip past them to the carat weight.

Carat is a measure of mass, not size. Antique cuts carry substantially more of their weight below the girdle than modern stones do, so they measure smaller across the top for the same weight. A 1.50ct old mine cut may span roughly 6.6–6.9mm where a 1.50ct modern round spans about 7.3mm.

The millimetre figures tell you what the stone will look like on a hand. The carat weight tells you what it will cost. These are different questions, and confusing them is the most common source of disappointment in antique diamond buying — covered further in our old mine cut price guide.

Why there is no cut grade, and why that is fine

This confuses buyers more than any other aspect of an antique report.

Laboratory cut grades are calculated only for standard round brilliants. The grade compares a stone's proportions against ranges derived from modern ideals for maximum brightness. Old mine cuts, old European cuts, rose cuts and every fancy shape sit outside that system, so the field comes back blank or marked not applicable.

Where a laboratory does apply a grade to a round-ish antique stone, it is worse than useless — it is actively misleading. The tall crown and small table that define an antique cut score badly against modern ideal ranges. A superb old European cut routinely receives a mediocre grade for being exactly what you want it to be.

Ignore the cut grade on an antique stone. Read the proportions instead, and trust your eye. Our explanation of why antique diamonds sparkle differently covers what those proportions actually do.

The proportions worth reading

Field	Modern ideal	Typical antique	What it means
Table %	54–60%	Often under 50%	Smaller table = more fire, less white brilliance
Crown angle	~34°	Frequently 38–42°	Taller crown = more dispersion
Depth %	59–63%	Often 60–70%	Deeper stone = smaller face-up spread
Culet	None / pointed	Medium to very large	Open culet dates the stone; visible as a dot
Girdle	Faceted, polished	Often bruted, frosted	Bruted girdle indicates hand cutting

Colour: apply antique logic

Colour is graded identically for antique and modern stones, from D through Z. What differs is what the grade should mean to you.

The modern market punishes warmth steeply, because a warm stone in a white metal setting under bright light reads as compromised. In antique cuts the discount is far shallower, for a straightforward reason: these stones were cut to sit in yellow gold under warm light, where faint warmth reads as intentional rather than as a defect.

Practically, if you are buying an antique stone for a yellow gold setting, the J to M range is the strongest value in the entire antique diamond market. You are paying substantially less for something that will look more coherent, not less.

Clarity: read the plot, not just the grade

Antique cuts hide inclusions well. The small table and chunky faceting break up light in a way a large modern table does not, so an SI1 or even SI2 old mine cut is frequently eye-clean where the same grade in a modern round is not.

What matters more than the grade is where the inclusions are, which is what the plotting diagram shows:

Under the table, centrally — most visible position; matters most
Near the girdle — often hidden by the setting, but a feather reaching the surface here is a structural concern on a century-old stone you intend to wear
Under the crown facets — usually well concealed

On an antique stone, prioritise structural safety over grade. A feather breaking the surface at the girdle is worth more attention than an SI2 designation.

Fluorescence: often an advantage here

Fluorescence is the visible glow some diamonds show under ultraviolet light, most commonly blue. It has been discounted in the modern market for decades, and fluorescent stones trade below non-fluorescent equivalents.

For antique cuts this frequently works in your favour. Blue fluorescence can make a faintly warm stone appear whiter in daylight — which is exactly the situation with a J or K colour antique stone. You get a visual improvement and a price discount simultaneously.

The caveat: a small proportion of strongly fluorescent stones look slightly hazy or oily in sunlight. This is uncommon but real. View any stone graded strong or very strong fluorescence outdoors before buying.

Read the comments section

The comments are the least-read and often most informative part of a report. Look for notes on additional facets, surface graining, clouds not shown on the plot, and — critically — any indication that the stone has been laser drilled, fracture filled or otherwise treated.

For antique stones, the comments may also describe the cutting style, which is the report's most useful contribution to dating.

The four things no report will tell you

This is the part that decides price, and none of it appears on the document.

Whether the stone is original to the setting. A report describes a stone. It says nothing about the ring around it. A modern stone in an antique mount and an antique stone in a modern mount are different objects at different prices.
Whether it has been recut. Antique stones are frequently recut into modern shapes, and recut stones carry an old provenance but are, functionally, modern diamonds. Nothing on a report distinguishes them.
How it actually looks. No combination of numbers predicts how a stone performs in a real room. Two stones with identical specifications can look meaningfully different.
Its era. The cutting style is evidence, not proof. Dating requires reading the whole piece — our guide to dating an antique ring covers the method.

Practical rules

Check the report is current and matches the stone. Compare measurements and inclusions against what you are holding. Reports are transferable documents; stones get swapped.
Verify the report number online with the issuing laboratory. This takes a minute and catches altered documents.
Know which document you have. An abbreviated report or dossier omits the plotting diagram, which is a real loss on an antique stone.
Do not expect reports on small accents. Grading requires the stone to be unset. Nobody removes melee from a period ring to certify it, and asking for it signals inexperience.
Treat an old report cautiously. Grading standards and laboratory consistency have shifted over decades. A report from the 1980s is a historical document rather than a current assessment.

Questions people actually ask

Why does my antique diamond have no cut grade?

Cut grades are calculated only for standard round brilliants. Antique cuts and fancy shapes fall outside the system. It is not a criticism of the stone.

Is fluorescence bad?

Usually not, and on a faintly warm antique stone it can help by making it read whiter in daylight. View strongly fluorescent stones in sunlight first.

Does a report prove the diamond is antique?

No. It may identify the cutting style, which is strong evidence, but it cannot tell you whether the stone is original to its setting or has been recut.

Should I insist on a report?

For a significant centre stone, yes — or a return window long enough to obtain one. For accent stones in a period setting, no.

What if the report grade and my eye disagree?

On an antique stone, trust your eye. The grading system is calibrated for a stone yours is not.

If you have a report and want a second view on what it actually says about the stone, send it over. And if you are hunting a specific certified antique diamond, that is what sourcing is for.