Showing 6 of 6
Round Cut Loose Diamonds
ラウンドカットダイヤモンドルース
-
Natural Loose Natural Diamond 1.102ct Light Yellow S Round
Regular price ¥480,000 (Tax incl.)Unit price per -
Natural Loose Natural Diamond 0.523ct Very Light Purplish Pink Round
Contact us for price inquiry.
-
Sold outNatural Loose Natural Diamond 1.053ct Near Colorless H Round
Regular price ¥540,000 (Tax incl.)Unit price perSold out -
Sold outNatural Loose Natural Diamond 1.024ct Near Colorless I Round
Regular price ¥620,000 (Tax incl.)Unit price perSold out -
Sold outNatural Loose Natural Diamond 1.05ct Near Colorless G Round
Regular price ¥740,000 (Tax incl.)Unit price perSold out -
Sold outNatural Loose Natural Diamond 1.069ct Colorless F Round
Regular price ¥980,000 (Tax incl.)Unit price perSold out
How to Choose a Round Brilliant Cut Loose Diamond
Why Round Brilliant Remains the Standard
The round brilliant cut was mathematically formalized by Marcel Tolkowsky in 1919, establishing the proportions that would maximize light return from a diamond's 58 facets. It remains the most produced and most purchased diamond shape globally for two reasons that reinforce each other: it produces the strongest sparkle of any shape — achieving the highest possible combination of brilliance (white light reflection), fire (color dispersion), and scintillation (point-by-point flashes of light) — and it is the most universally recognized shape in the diamond market, which makes it the most liquid asset and the safest choice for buyers who want both aesthetic quality and long-term value retention. Our round brilliant cut loose collection focuses exclusively on 1ct and above, with CGL certification across all stones.
The GIA Cut Grade — Round Brilliant's Unique Advantage
Round brilliant cut is the only diamond shape for which GIA formally assigns a cut grade: Excellent, Very Good, Good, Fair, or Poor. No other shape — not cushion, not oval, not emerald, not radiant — receives a GIA cut grade. This makes round brilliant uniquely evaluable on an objective scale, and it is the single most important factor when selecting a round loose diamond. An Excellent cut diamond returns more light than a Very Good cut stone of identical color and clarity, and that difference is perceptible to the naked eye under most lighting conditions. The price difference between an Excellent and Very Good cut stone reflects this — and it is a price difference that can be verified empirically by viewing the two stones side by side. When selecting from our collection, we recommend prioritizing cut grade above color and clarity, then optimizing color and clarity within budget. F and G color grades represent the best balance of visual quality and value for round brilliant cut in white metal settings; I color performs well in yellow gold. VS2 and SI1 clarity are both eye-clean in most round brilliant cut stones at 1ct, making either appropriate for engagement ring purposes.
The 1ct Threshold — Why It Matters
The 1ct threshold is worth understanding regardless of which stone you are considering. It is meaningful both visually and commercially. Visually, the difference between a 0.9ct and a 1.0ct round brilliant cut diamond is perceptible on the hand in a way that the difference between 0.8ct and 0.9ct generally is not — the stone's face-up diameter crosses a threshold at 1ct that reads as meaningfully more present. Commercially, 1ct round brilliant cut diamonds with GIA certification occupy one of the most liquid segments of the international diamond market, with an established global price reference (Rapaport Report) and active buyer demand across auction houses, dealers, and private markets. This liquidity is specific to round brilliant cut — it is markedly stronger than for any fancy shape. Buyers purchasing for investment or long-term asset holding will find 1ct+ round brilliant cut GIA Excellent grade stones in D-F color and VVS-VS clarity to be among the most defensible categories available. Contact us to discuss current inventory or investment-oriented purchasing.
Frequently Asked Questions
Round brilliant cut is a mathematically formalized diamond shape established in 1919 by Marcel Tolkowsky, with 58 facets optimized to maximize light return. It produces the strongest sparkle of any diamond shape — the highest combination of brilliance, fire, and scintillation — and is the most purchased diamond shape globally for engagement rings. It is the only shape for which GIA formally assigns a cut grade.
The GIA cut grade — Excellent, Very Good, Good, Fair, or Poor — is formally assigned only to round brilliant cut diamonds. No other shape receives this grade. An Excellent cut stone returns more light than a Very Good cut stone of identical color and clarity, and the difference is perceptible to the naked eye. This makes cut grade the single most important evaluation factor for round brilliant cut, more important than color or clarity within the same price range.
F and G color grades offer the best balance of visual quality and value for round brilliant cut in white gold or platinum settings. The difference from D or E color is difficult to detect with the naked eye, allowing the same budget to be allocated to a higher cut grade or larger carat weight. I color performs well in yellow gold settings. All color grades from D through J appear white in round brilliant cut under most lighting conditions when set appropriately.
Round brilliant cut diamonds of 1ct and above with GIA certification occupy one of the most liquid segments of the international diamond market, with an established global price reference and active demand across international dealers and auction houses. This liquidity is markedly stronger than for any fancy cut shape. For investment purposes, Excellent cut grade in D-F color and VVS-VS clarity represents the most defensible combination. Contact us to discuss investment-oriented purchasing.
Yes. All round brilliant cut loose diamonds at Weiss carry CGL certification, documenting color grade, clarity, carat weight, and cut grade. The cut grade — unique to round brilliant cut among all diamond shapes — is one of the most important data points on the certificate for purchase evaluation.
The 1ct threshold is significant both visually and commercially. Visually, the face-up diameter of a 1ct round brilliant cut reads as meaningfully more present on the hand than a 0.9ct stone. Commercially, 1ct+ round brilliant cut diamonds occupy the most liquid segment of the international diamond market, with stronger global price references and buyer demand than either smaller sizes or other shapes.
Yes. Our appointment-only office is in Okachimachi, Tokyo. For round brilliant cut, viewing in person allows you to compare the actual light return difference between cut grades — a comparison that certificate data describes but cannot substitute for direct observation. Please book an appointment through our contact page or by phone.
Prefer a finished piece? See our Round cut Diamond Rings.