The 4Cs of Diamonds
ダイヤモンドの4Cガイド
What are the 4Cs?ダイヤモンドの4Cとは
The 4Cs stand for Carat, Color, Clarity, and Cut. Used worldwide, they are the universal criteria for assessing diamond quality — a shared language for objectively judging the brilliance and value of each stone. Lab-grown diamonds are graded to exactly the same standards as natural diamonds.
Caratカラット ― 重さ
Carat (ct) is a unit of weight, not size — one carat equals 0.2 grams. The word derives from the carob seeds once used as counterweights for weighing gems. Diamonds of the same carat weight can appear different in size depending on the depth of their cut. Use the slider to compare approximate diameters.
0.30 ct
Approx. diameter 4.5 mm (round brilliant)
PRMAL engagement rings are available with diamonds from 0.3 ct.
Colorカラー ― 色
Diamond color is graded on a 23-step scale, from colorless “D” down to “Z” with a faint yellow tint. The closer to colorless, the rarer the stone — and the more purely it transmits light, the higher it is valued. Grades D through F are called “colorless,” and G through J “near colorless.”
All PRMAL diamonds are G color or higher, and engagement ring center stones are exclusively F color or higher — within the colorless range.
Clarityクラリティ ― 透明度
Clarity measures the absence of inclusions and surface blemishes. Diamonds are graded on an 11-step scale under 10x magnification, based on the number, size, and position of these characteristics. Nearly every diamond has its own unique inclusions, but at VS2 and above they are rarely visible to the naked eye.
Every PRMAL diamond, including engagement ring center stones, is VS2 or higher — clarity with no inclusions visible to the naked eye.
Cutカット ― 輝き
Cut is the only one of the 4Cs created by human hands. It is graded on three elements — proportion, symmetry, and polish. An ideally cut diamond reflects light completely within the stone and returns it as maximum brilliance. Cut too shallow or too deep, and light escapes from the bottom.
Cut too shallow — light escapes through the bottom, weakening the brilliance.
Ideal proportions — light is fully reflected back.
Cut too deep — light leaks out through the sides.
All PRMAL diamonds are graded Good or higher, and engagement ring center stones are exclusively Excellent — the highest grade. *Cut grading applies to round brilliant cut diamonds.
Our 4Cs Standardダイヤモンド品質基準
Every center stone in a PRMAL engagement ring comes with a grading report from IGI, the International Gemological Institute. Within the global 4Cs standard, we select only the following grades.
- Carat
- 0.3 ct +
- Weight — available from 0.3 carats
- Color
- F or higher
- Color — F or higher, within the colorless range
- Clarity
- VS2 or higher
- Clarity — no inclusions visible to the naked eye
- Cut
- Excellent
- Cut — only the highest grade, Excellent
Diamonds used in all other PRMAL jewelry — including melee diamonds in earrings and necklaces — are likewise limited to G color or higher, VS2 or higher, and Good cut or higher.
History of Diamond 4Cs4Cが世界基準になるまで
Until the early 20th century, the language used to describe diamond quality varied from country to country and merchant to merchant. The 4Cs standard, established by the Gemological Institute of America (GIA) in the 1950s, ended that confusion and opened an era in which anyone in the world could choose a diamond by the same measure. Today, international institutes such as IGI certify the quality of lab-grown diamonds to that very same standard.
The First Diamond Ring
The ring Archduke Maximilian of Austria gave to Mary of Burgundy is considered the first recorded diamond engagement ring. At the time, no common standard for measuring quality yet existed.
GIA Founded
Robert Shipley founds the Gemological Institute of America (GIA), establishing gemology as a formal discipline and paving the way for fair grading standards.
The Term “4Cs” Coined
Shipley coins the term “4Cs” — Carat, Color, Clarity, Cut — as a mnemonic to help his students remember the factors of diamond quality. It began as a teaching device.
International Grading System
GIA’s Richard Liddicoat introduces the GIA Diamond Grading System, with its distinctive color scale deliberately beginning at “D.” The 4Cs become the grading standard shared worldwide.
The First Lab-Grown Diamond
General Electric succeeds in creating the world’s first lab-grown diamond. Though initially for industrial use, it proved that the same crystal as a natural diamond could be grown in a laboratory.
IGI Founded
The International Gemological Institute (IGI) is founded in Antwerp, Belgium. Expanding into the world’s major gem trading cities, it grows into one of the largest gemological institutes in the world.
IGI Grades Lab-Grown Diamonds
IGI becomes the first major institute to issue full grading reports for lab-grown diamonds, applying the same 4Cs criteria used for natural diamonds.
A Diamond Is a Diamond
The U.S. Federal Trade Commission removes the word “natural” from its definition of a diamond. Lab-grown diamonds are officially recognized as diamonds, graded by the same 4Cs as natural stones.
PRMAL Launched
PRMAL launches in Japan as a jewelry brand embracing lab-grown diamonds — offering only carefully selected, high-quality diamonds based on the 4Cs, the global standard passed down for over half a century.
FAQ
Diamond 4Cs Q&A4Cについてよくあるご質問
All four matter, but at PRMAL we place particular importance on Cut. Cut is the only one of the 4Cs that determines how a diamond reflects light and how beautifully it sparkles. Even at the same carat weight, a diamond’s appearance changes dramatically with its cut.
Yes. Even with identical 4Cs, brilliance and overall appearance vary with the balance of the cut, its symmetry, and polish. PRMAL selects each stone by confirming its actual beauty, not just its grades.
For engagement ring center stones, which come with a grading report, PRMAL uses lab-grown diamonds of F color or higher, VS2 or higher, and Excellent cut — the highest grade. For melee diamonds and other jewelry, we use lab-grown diamonds of G color or higher, VS2 or higher, and Good cut or higher. Beyond the grades, we also inspect brilliance and proportions, hand-selecting every stone.
Yes. Like natural diamonds, lab-grown diamonds can be graded by the International Gemological Institute (IGI). Every PRMAL engagement ring comes with a grading report, and eligible jewelry — such as earrings and necklaces with diamonds of 0.5 ct and above — also includes an IGI report.
The report documents the 4Cs — carat, color, clarity, and cut — along with the diamond’s other characteristics, all assessed to international standards, serving as objective third-party proof of quality. Products that include a report are marked as such on the product page, so you can easily check before you buy.
No. Like natural diamonds, each lab-grown diamond has its own individual character. Minute inclusions and surface blemishes can form during the growth process, so not every stone is flawless.
PRMAL uses only diamonds meeting strict standards — F color or higher, VS2 or higher, and Excellent cut — for engagement ring center stones. At normal wearing distance, inclusions are rarely visible to the naked eye, and you can simply enjoy the beautiful brilliance.
No. A lab-grown diamond itself will not cloud or lose its brilliance over time. Lab-grown diamonds are crystals of pure carbon, identical to natural diamonds in their physical, chemical, and optical properties, so the diamond itself will never discolor or become cloudy.
If a diamond seems less brilliant, the cause is almost always surface residue from skin oils, hand cream, or cosmetics. Gently washing it in lukewarm water with a diluted mild detergent will restore its original brilliance.
No. They share the same hardness and crystal structure as natural diamonds, so there is no difference in durability. That said, while diamonds are extremely hard, a strong impact can chip any diamond — natural or lab-grown alike.
Carat is a unit of weight: one carat equals 0.2 grams. Higher carat weights are generally rarer, but carat measures weight only — it does not determine a diamond’s size or beauty. Diamonds of the same carat weight can differ in apparent size and brilliance depending on their cut proportions.
Diamonds generally become more expensive as carat weight increases, so choose the diamond that best suits your taste and lifestyle.
Color grading measures how close a diamond is to colorless. On the international scale, grades run alphabetically from D — the most colorless — down to Z, as yellow or brown tints gradually appear. Trained graders judge minute differences in color under controlled lighting, comparing each stone against a set of master stones. In everyday wear, differences among grades D through G are considered very difficult to distinguish with the naked eye.
PRMAL uses only diamonds of G color or higher — beautifully near colorless, with an excellent balance of quality and price. We value quality standards that never compromise on beauty while remaining easy to wear every day.
Cut quality evaluates how efficiently a diamond takes in light and returns it as brilliance. The assessment considers multiple factors together: table size, crown and pavilion angles, overall proportions, symmetry, and polish.
However fine its color and clarity, a diamond with poorly balanced cut cannot show its full brilliance. PRMAL selects diamonds to a high standard and confirms their actual brilliance and balance, bringing out the full natural beauty of each stone.
Because we value not only beauty and quality, but also making a choice fit for the times ahead. We believe lab-grown diamonds offer the same beauty as natural diamonds while being one of the more sustainable options.
