The four Cs - Carat (weight), Color (D-Z and fancy colors), Clarity (FL to I grades) and Cut (proportions affecting brilliance, fire and scintillation) - remain the core of diamond grading. Modern practice emphasizes cut as the most visible factor for sparkle, while color and clarity scales (and carat measurements in 0.2 g units) help buyers compare stones. Balance the Cs based on budget and visual priorities, and request a report from a recognized lab such as GIA or AGS.

The four Cs - the foundation of diamond grading

When people ask why diamonds captivate us, the short answer is: the four Cs. Carat, Color, Clarity and Cut are the standardized qualities gemologists use to describe and compare diamonds. They explain most of what affects a stone's appearance and value.

Carat (weight)

Carat measures a diamond's weight: one carat equals 0.2 grams (200 milligrams). The trade also uses a point system where 1 carat = 100 points, so a 0.75-carat stone is 75 points. Historically, people compared gems to carob seeds for a consistent reference, but today the metric carat (0.2 g) is the universal standard.

Color (hue and intensity)

Most gem-quality white diamonds are graded on a scale from D (colorless) to Z (light yellow or brown). Stones that show strong, distinct colors - pink, blue, red, green, or intense yellow - are classified as fancy-color diamonds and are graded and priced differently than D-Z white diamonds. In general, the less tint a white diamond shows, the higher its grade on the D-Z scale.

Clarity (inclusions and blemishes)

Clarity describes internal features (inclusions) and surface marks (blemishes) that formed as the diamond grew. These "fingerprints of nature" make each diamond unique. The most widely used clarity scale (from best to lower) is: Flawless (FL), Internally Flawless (IF), Very Very Slightly Included (VVS1-VVS2), Very Slightly Included (VS1-VS2), Slightly Included (SI1-SI2), and Included (I1-I2-I3). FL and IF indicate no internal inclusions visible under 10× magnification. The trade also uses terms like "eye-clean" to describe diamonds that show no visible inclusions to the naked eye.

Cut (proportions, finish, and optical performance)

Cut is where human skill plays the biggest role. A diamond's facets, angles and proportions determine how light interacts with the stone - how much brilliance (white light return), fire (colored flashes), and scintillation (sparkle) it shows. Professional labs like GIA grade cut for round brilliants (e.g., Excellent, Very Good, Good, Fair, Poor), while other labs such as AGS use numerical systems. Poor proportions can cause light to leak out the sides or bottom, reducing sparkle; a well-cut diamond concentrates light back through the table, maximizing visual performance.

Putting the Cs together

No single C determines value or beauty on its own. Buyers balance carat with color and clarity preferences and prioritize cut to maximize visible sparkle for the budget. For many shoppers, a slightly lower color or clarity with an excellent cut delivers more perceived beauty than a higher-graded stone with poor proportions.

Practical tips

  • Ask for a grading report from a recognized lab (e.g., GIA or AGS).
  • Prioritize cut for visible brightness and sparkle.
  • Use carat points and milligrams to understand exact weight.
  • Consider "eye-clean" SI stones or slightly lower color grades to get more carat for your budget.

FAQs about Diamonds Are Forever

What exactly is a carat and how does it relate to grams?
A carat is a unit of weight equal to 0.2 grams (200 milligrams). The diamond trade also uses a points system where 1 carat = 100 points (e.g., 0.75 carat = 75 points).
How does the color grading scale work?
Most white diamonds use the D-Z scale, where D is colorless and Z shows noticeable yellow or brown tint. Strongly colored stones (pink, blue, intense yellow) are graded as fancy-color diamonds and follow a different valuation approach.
What does "eye-clean" mean compared with graded clarity like VVS or SI?
"Eye-clean" means no inclusions are visible to the unaided eye at normal viewing distance. Graded clarity (FL, IF, VVS, VS, SI, I) is assessed under 10× magnification. A diamond can be SI but still appear eye-clean, which can offer better value.
Is cut more important than carat, color or clarity?
Cut is often the most important factor for perceived beauty because it controls how the diamond returns light. A well-cut smaller stone can look more lively than a larger, poorly cut one. Buyers commonly prioritize cut to maximize sparkle within their budget.