Diamond Buying Guide: How to Choose a Diamond
Diamond grading rests on four factors: cut, color, clarity, and carat weight. The scales behind them arrived separately over sixty years. Two of the four do not apply to a large share of the diamonds in an estate collection.
A grading report describes a stone under controlled laboratory light. It does not describe how the diamond behaves on a hand, in a room, in the metal it is set in. Both readings are necessary. They answer different questions.
This guide covers each factor in turn, then the shapes and the hand-cut antique stones the scales were never written for. Each section links the full guide and the matching collection of what is currently in stock.
The 4Cs
Cut, color, clarity, and carat weight are the four factors gemologists use to grade a diamond. They were never a single invention. Robert Shipley coined the phrase in the 1940s as a teaching device. GIA formalized the color and clarity scales in 1953, and cut grading for round brilliants did not exist until 2006. Reading the four as one unified standard is what leads buyers to weigh them as equals.
Cut
Cut grades how well a diamond's facets were proportioned, angled, and finished. It is the only one of the four a person decided rather than geology, and the most visible of them: a step down in cut shows at arm's length, where a step down in color or clarity usually does not. GIA grades it on round brilliants alone. Every fancy shape leaves that line blank.
Color
Diamond color is graded D to Z and measures the absence of hue rather than its presence. The grade is fixed; what is visible is not. A diamond's facets pick up the color of the band and prongs. A J in yellow gold can read as white on the hand as a G in platinum. The setting metal is a larger factor than the letter on the report.
Clarity
Clarity grades the inclusions a trained grader finds at 10x magnification, on an eleven-step scale from Flawless to Included. Most diamonds sold fall in the VS to SI middle. The grade records what a loupe found rather than what the eye sees. Position matters as much as size. Step cuts like emerald and Asscher need a higher grade than a brilliant, because open facets conceal nothing.
Carat
One carat is exactly 200 milligrams, divided into 100 points. It measures mass, not the width a viewer registers. Weight accumulates in the pavilion and girdle where it cannot be seen. Two diamonds of identical weight can therefore face up at different sizes. Girdle diameter in millimeters is the figure that describes apparent size. Price rises out of proportion at 1.00, 1.50, and 2.00 carats.
Diamond Shapes
Shape is the outline; cut is the quality of the facet work beneath it. Marcel Tolkowsky fixed the round brilliant's proportions in 1919. That standardization is the only reason a cut grade exists at all. Oval, cushion, emerald, Asscher, princess, marquise, pear, and radiant are fancy shapes with no grade, judged instead on length-to-width ratio, depth, and the bow-tie effect.
Vintage Cuts
Old Mine, Old European, and rose cut diamonds were shaped by hand for candlelight, long before any scale existed to grade them. None carries a cut grade. The blank line marks the limit of the report rather than a judgment on the stone. Three checks replace it: whether the facets sit roughly even, whether the girdle has taken a real chip, and how the stone behaves under soft light.
Salt & Pepper
Salt and pepper diamonds are natural diamonds carrying enough visible inclusions to be seen without magnification: graphite in black, sulfide minerals in pale grey. The clarity scale grades the absence of exactly what these stones are selected for, so it places them at I2 or I3 and stops there. Pattern, tone, transparency, and cut quality replace the grade.
The Full Buying Guide
The complete guide: the four graded qualities and the several ungraded ones. It covers where to start, what a grading report does and does not state, why antique stones often carry none, and how shape, era, and setting change the decision. The sections above cover each factor on its own.
Diamond Engagement Rings in Stock
Every diamond photographed in daylight, verified, authenticated, and shipped insured anywhere in the country.
Tuesday–Friday 11AM–6PM · Saturday 11AM–5PM
Choosing a Diamond, Answered
Where should you start when choosing a diamond?
Cut, because it has the largest effect on how a diamond looks at ordinary viewing distance and it is the only one of the 4Cs a cutter decided. Color and clarity have a ceiling: once a stone is eye clean and near colorless, further improvement registers on the report rather than on the hand. Carat is the most personal of the four, since it answers to the hand and the setting.
Do your diamonds come with GIA grading reports?
Many do, and a large share of the antique and estate stones do not. GIA grades loose stones only. Certifying a mounted diamond means unsetting it, which puts an original century-old setting at risk. An uncertified stone is a legitimate option rather than a lesser one. Filigree's staff is GIA-trained, and the same published criteria apply to a stone examined in person.
What does GIA not grade?
Cut on any shape other than a round brilliant. Every oval, cushion, emerald, Asscher, marquise, pear, and radiant leaves that line blank. Antique cuts are excluded for the same reason, since Old Mine, Old European, and rose cuts predate the standard entirely. Salt and pepper diamonds sit outside the useful range of the clarity scale as well.
How do you compare two diamonds that look identical on paper?
By looking at them together under the same light. Two stones can carry matching grades and measurements and still differ, because a grade records a laboratory's finding under controlled light and says nothing about how a stone behaves in a room. Position of an inclusion, the metal holding the stone, and the cut each move the result.
Are vintage diamonds durable enough for an engagement ring?
Yes. Diamond rates 10 on the Mohs scale. A stone cut in 1890 is exactly as hard as one cut last year. Wear risk comes from shape and setting rather than age: pointed corners on a marquise or pear need protective prongs, and any antique ring should have its prongs checked before daily wear.
Can you see these diamonds in person?
Yes. The showroom is at 210 N. 2nd Street in Minneapolis, open Tuesday through Friday 11AM to 6PM and Saturday 11AM to 5PM. Every piece is also photographed in daylight and shipped insured anywhere in the country. Each collection linked above shows what is currently in stock.
Store Hours
Tuesday-Friday: 11AM-6PM
Saturday: 11AM-5PM
Sunday-Monday: Closed
Phone: 612-486-2290
Email: info@filigreejewelers.com
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Getting Here
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Our Address:
Filigree Jewelers
210 North 2nd Street, Suite 101
Minneapolis, MN, 55401 -
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