How do I know if a diamond is good quality?

Most people shop for diamonds backwards. They fixate on carat weight and clarity grade first, then color, and treat cut as a footnote. Cut is the only one of the 4Cs that a human being controls, and it fundamentally determines whether the stone looks alive or dead. Start there. A 1.00 carat G/VS2 with ideal proportions will outshine a 1.50 carat D/IF with poor angles every single time.

For a modern round brilliant, I want a GIA triple excellent, but even that is just the starting line. The grade covers a range. I look for a table between 54% and 57%, a crown angle around 34 to 35 degrees, and a pavilion depth near 43%. Those numbers tend to produce the balanced fire and brightness that make a diamond interesting. If you're buying online and the vendor won't give you an ASET or Idealscope image, walk away. A video in diffused lighting is the next best thing. Fancy shapes don't get a cut grade from GIA at all - for ovals, pears, and cushions, you need to see the stone move and confirm the bowtie isn't swallowing the center.

Color is simpler than people make it. In a white gold or platinum solitaire, I'll push a client to H or better. If the ring is yellow gold, you can drop to I or J and still see no warmth face-up. Faint color is most visible from the side profile, and no one looks at a ring sideways. D, E, and F are colorless, sure, but a clean G or H splits the difference on price and gets you more stone for the same budget.

Clarity should mean eye-clean, not flawless. A well-placed SI1 with a feather near the girdle beats a VS2 with a black crystal dead center under the table, and I've seen that mistake cost people real money. Last spring, a client named Priya brought in a 1.20 carat VS2 she'd bought online. The report plot showed a tiny inclusion symbol, but the thing was a black speck visible from across a restaurant table. We sent it back after one evening. The replacement was an SI1 with a white feather at the edge - invisible without a loupe, and $600 less. The GIA plot gives you a map; it doesn't tell you where your eye will land.

Fluorescence is the wildcard most buyers ignore. Medium blue can make an I-color diamond look whiter, which is useful. Strong blue in a D-F stone sometimes creates a hazy, oily look, but not always. I won't buy a stone with strong fluorescence sight unseen. You have to hold it.

Lab-grown diamonds follow the same visual rules, though most are graded by IGI. CVD-grown stones can show subtle strain lines; HPHT material is often cleaner but trickier to find in certain sizes. The price gap keeps widening, and if you're spending over $3,000 on a lab diamond smaller than two carats, you're probably paying too much.

The only way to know if a diamond is good quality is to look at it in natural daylight, next to another stone, with a loupe and a little time. A GIA report opens the door. Your eyes have to walk through it.