Diamonds are among nature’s most precious and beautiful creations. But with all the glamour comes a few flaws that might result in a diamond losing its shine. To maintain the quality of diamonds, it‘s important to understand their properties and common defects, as well as learn about the advanced technology used to measure them.
Here we shine a light on diamonds, highlighting what they’re made of, exploring their common flaws, and zooming in on the details of these flaws using two different inspection tools—digital microscopes and laser confocal microscopes.
What Is a Diamond Made of?
A diamond is a solid form of carbon with its atoms arranged in a crystal structure called diamond cubic (atoms arranged in a tetrahedral 3D network). Diamonds are formed deep within the Earth's mantle, typically around 150–200 kilometers (93–124 miles) below the surface, under high pressure and temperature conditions.
Due to the formation conditions and distinct atomic structures, diamonds have the highest hardness and thermal conductivity of any natural material. These properties are used in major industrial applications, such as cutting and polishing tools. Rough diamonds are mined and converted into gems through a multi-step process known as cutting.
Diamonds are rigid but brittle. They can be split up by a single blow. Therefore, diamond cutting is traditionally considered a delicate procedure requiring skills, knowledge, tools, and experience. Diamond cutting requires precision and expertise to maximize the diamond's optical properties and minimize weight loss during cutting. Its final goal is to produce a faceted jewel where the specific angles between the facets optimize the diamond’s luster (i.e., the dispersion of white light).
Diamonds are cut into a variety of shapes, such as round brilliant, pear (or teardrop), marquise, oval, and hearts and arrows. The value of a diamond is determined by a combination of factors known as the 4 Cs: cut, color, clarity, and carat weight. Various American certification agencies certify the quality of the diamond.
What Are the Types of Diamond Flaws?
The imperfections in diamonds can be classified as external and internal flaws. Diamond imperfections are assessed and graded by certified gemologists using standardized grading criteria. The severity, size, location, and type of imperfections can affect a diamond's clarity grade. Some diamond flaws include:
External diamond flaws
- Blemishes: These diamond flaws are present on the surface of a stone and can occur naturally.
- Scratches: These are fine lines found on the surface of the diamond. They may be present naturally or caused when a diamond is cut.
- Extra facets: These are usually cut to remove blemishes or inclusions. At times these different facets are also cut to enhance the brilliance of the diamond.
- Fracture: A breakage in diamonds that’s not parallel to the cleavage plane is a fracture. Fractures are usually irregular in shape, making a diamond look chipped.
- Fingerprints: Fingerprint inclusions in the shape of fingerprints are sometimes found in diamonds. However, these inclusions are rare in diamonds compared to other stones, such as rubies.
- Pits: Small holes may be present on the surface of a diamond. These pits are usually not visible to the naked eye.
- Nicks: Diamonds are also chipped at places, causing the appearance of nicks. Nicks are often repaired by adding extra facets.
Internal diamond flaws
- Crystal/mineral inclusions: Some diamonds show the presence of tiny crystals, minerals, or other diamonds.
- Pinpoint inclusions: As the name implies, these inclusions are minute crystals, usually white, found inside the diamond.
- Needles: Diamond crystals in a diamond can be present in the form of long and thin needles. These needles may not be visible to the naked eye.
- Cloud: The presence of three or more pinpoint inclusions close together can create a hazy area, or a cloud, in the diamond.
- Knots: When diamond crystals extend to the surface of the diamond, they are referred to as knots. These knots can be viewed under proper lighting conditions with a diamond loupe.
- Graining: Crystal inclusions in diamonds occur in the form of lines known as graining. Graining should not be confused with a rough diamond’s natural grain lines.
5 Ways to Detect Diamond Flaws Using a Microscope
To determine a diamond’s defects and improve quality control, we can turn to technologically advanced solutions, such as a digital microscope and laser confocal microscope.
DSX1000 digital microscope.
For example, our DSX1000 digital microscope seamlessly captures images under a wide variety of observation modes, including brightfield, oblique, darkfield, and differential interference contrast (DIC), to show the scratches on a diamond’s surface. We can also use the digital microscope with polarized light to explore other kinds of internal or external flaws, such as inclusions, fractures, and pits.
Here’s a brief overview of these methods for flaw detection on a diamond:
1. Brightfield observation
Reflected light brightfield is a commonly used method for viewing diamond flaws due to its simplicity and effectiveness in illuminating samples. The diamond sample appears bright against a dark background, providing contrast that enhances the visibility of flaws and inclusions within the diamond. This contrast makes it easier to detect imperfections such as fractures, inclusions, or other structural irregularities.
Brightfield observation of a diamond flaw with a DSX10-SXLOB3X objective.
Brightfield can also be used in conjunction with other imaging and illumination techniques to get a more comprehensive understanding of a diamond's characteristics. For example, you can combine brightfield observation with polarized light, darkfield, DIC, or oblique illumination to examine different aspects of the stone's structure and identify a wider range of flaws and inclusions. The image below shows a snapshot of a diamond under both brightfield and darkfield.
MIX observation of a diamond using a combination of brightfield and darkfield. Captured using the DSX1000 digital microscope.
2. Darkfield observation
Reflected light darkfield is a valuable observation method for viewing diamond flaws because it provides enhanced contrast and sensitivity to surface irregularities and inclusions. The diamond sample appears dark against a bright background due to the oblique angle of illumination. This high-contrast lighting technique accentuates surface features and imperfections, making even subtle flaws more visible.
As a result, darkfield observation is particularly effective for detecting surface scratches, abrasions, polishing marks, and other external blemishes on diamonds. As shown in the image above, darkfield observation complements brightfield by providing a different perspective on the diamond's surface and internal structure.
3. DIC observation
DIC observation can enhance the contrast of transparent and semi-transparent specimens, such as diamonds. In diamond examination, DIC observation can reveal fine structural features and flaws within the stone with high contrast and clarity. Here are some examples:
DIC observation of a diamond flaw. Captured using a DSX1000 digital microscope with a DSX10-SXLOB3X objective.
DIC observation of a diamond flaw. Captured using a DSX1000 digital microscope with an MPLFLN5XBDP objective.
DIC observation of diamond flaws. Captured using a DSX1000 digital microscope with an MPLAPON50X objective.
4. Oblique observation
Oblique observation involves tilting the diamond at an angle and illuminating it from the side rather than directly from above. This technique exploits the diamond's reflective properties to reveal flaws that may not be easily visible under normal lighting conditions.
By casting shadows and creating highlights, oblique illumination can accentuate surface irregularities, such as scratches, abrasions, or polishing marks, as well as internal flaws near the surface. Oblique observation is especially effective for assessing the overall condition and finish of a diamond, providing insights into its history of wear and potential durability issues.
Oblique observation of a diamond flaw. Captured using a DSX1000 digital microscope with a DSX10-SXLOB3X objective.
5. Polarized light observation
Polarized light is an effective method to detect diamond flaws because of the way it interacts with the crystal structure of diamonds. As the polarized light passes through the diamond, its birefringent properties cause the light waves to split into two components, each vibrating in a different direction and traveling at different speeds. This differential behavior can highlight internal flaws, such as fractures, inclusions, or crystal growth anomalies, by producing contrasting patterns or
colors in the diamond.
Surface Roughness Observation and Measurement of Diamonds
The DSX1000 digital microscope offers a 1750X view, which sufficiently lets us see deformations such as a scratch on the surface of the diamond. To find the roughness information for these surface areas in the nanometer scale, we can switch to confocal laser scanning microscopy.
For instance, our LEXT™ OLS5100 3D confocal laser microscope employs a 405 nm laser source to scan the sample using the confocal technique, capturing precise height information of a diamond’s surface. See the confocal image and surface roughness data below as an example.
Surface roughness observation of a diamond at 2500X magnification. Captured using the LEXT OLS5100 3D confocal laser microscope.
From the report below, we can conclude that the roughness value (Ra) is 20 nm. The maximum peak (Rp) observed is 58 nm, and the maximum valley (Rv) is 49 nm.
In conclusion, choosing the right microscope system and observation method can help inspectors identify defects and accurately perform measurements for the quality control of diamond production.
Portions of this content have been adapted from a blog post written by Gyanesh Singh, application specialist at IR Technology Services Pvt. Ltd. Read the original post, Surface Roughness Observation of a Diamond.
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