GIA Gemology Guide: Cloud Inclusions in Diamonds

For a GIA student or professional jewelry appraiser, identifying and evaluating internal characteristics is fundamental to diamond grading. A cloud is a very common inclusion that requires careful assessment, as its impact can range from completely negligible to severely detrimental to a diamond's overall visual performance and transparency.

1. What is a Cloud?

A cloud is not a single structural break or void, but rather a broad term used to describe a tightly grouped cluster of tiny inclusions. These individual inclusions are typically "pinpoints" (microscopic crystals), but can sometimes be tiny cavities or microscopic feathers. Because they are so small and densely packed, they cannot be easily distinguished individually at 10x magnification; instead, they create a hazy, milky, or cloudy patch within the diamond.

How do they form?

Clouds are entirely natural and form deep within the earth during the diamond's crystallization process. They occur when:

Microscopic trace minerals or internal structural anomalies are trapped in clusters as the diamond carbon lattice grows.
Changes in temperature or pressure during formation cause sudden bursts of tiny crystals to form in a specific zone before clear diamond growth resumes.

2. How to Plot a Cloud (GIA Standards)

Because a cloud is situated inside the diamond's crystal lattice, it is classified purely as an internal characteristic (inclusion) and is plotted using red ink.

Plotting Steps:

Locate the Feature: Using a microscope with darkfield illumination, locate the hazy or milky area. Clouds can sometimes be incredibly faint ("wispy") or quite dense and opaque.
Plot the Symbol: A cloud is plotted using a red dotted line that outlines the exact shape and extent of the hazy area as seen through the lens. If the cloud consists of a very small, loose grouping of pinpoints, you may simply draw a cluster of small red dots.
Determine Depth and View: Map the cloud on the crown (top) diagram if it is closer to the top, or the pavilion (bottom) diagram if it is located deeper. If it is large and spans a significant depth, it may be plotted on both.
Key to Symbols: "Cloud" is listed in the Key to Symbols. If the cloud is the primary reason for the diamond's clarity grade, it will be listed first.

3. Cloud vs. Similar Characteristics

It is important to differentiate clouds from other internal inclusions that are closely related:

Cloud vs. Pinpoint: A pinpoint (plotted as a single red dot) is an isolated, microscopic crystal. A cloud is simply a dense gathering of many pinpoints.
Cloud vs. Twinning Wisp: A twinning wisp (plotted as a squiggly red line, often with internal cross-hatching) is a growth defect that twists through the stone, often containing clouds, pinpoints, and crystals along its path. A cloud is a standalone hazy patch without the twisting, ribbon-like structure of a wisp.
Cloud vs. Crystal: A crystal (plotted as a solid red outline) is a distinct, individually resolvable mineral trapped inside the diamond. You can clearly see a crystal's boundaries at 10x magnification, whereas a cloud appears as a diffuse haze.

4. Evaluation and Appraisal Considerations

While chips, bruises, and cavities present durability risks, clouds are primarily evaluated based on how they interact with light. For appraisers and gemologists, a cloud's impact on transparency is a critical value factor.

Impact on Clarity Grade: A faint, small cloud might keep a diamond in the VVS or VS range. However, a large, dense cloud that spreads across the table will lower the grade into the SI or I (Included) categories.
The "Clarity Based on Clouds" Warning: On a GIA report, if an SI or I-grade diamond has no major inclusions plotted but has the comment "Clarity grade is based on clouds that are not shown," this is a major red flag for buyers and appraisers. It means the entire stone is so full of microscopic clouds that plotting them would obliterate the diagram.
Impact on Brilliance (The "Milky" Diamond): Dense clouds scatter light before it can return to the viewer's eye. A heavily clouded diamond will lose its signature crisp brilliance and fire, appearing "sleepy," "milky," or dull.
Appraisal Value: Two diamonds with the exact same SI2 clarity grade can have vastly different values. An SI2 graded due to a single, distinct black crystal hidden near the edge will trade at a premium over an SI2 graded due to a massive cloud that makes the stone look cloudy or dull. Appraisers must note reduced transparency, as heavily clouded stones trade at steep discounts in the wholesale market.

Summary for GIA Students

Definition: A hazy or milky area composed of tightly clustered, microscopic inclusions (usually pinpoints).
Plotting: A red dotted line outlining the shape of the cloud, or a tight grouping of red dots.
Key Factors: Assess the density of the cloud. Determine if the cloud is severely scattering light and causing the diamond to lose transparency and appear "milky" or "sleepy," which severely impacts value.