The Diamond Certification Laboratory of Australia (DCLA)

An octahedron is one of the most sought-after crystal shapes for rough diamonds, featuring eight triangular faces arranged symmetrically. This shape resembles two four-sided pyramids joined at their base, forming a perfect geometric structure. Due to its natural symmetry and efficient cutting potential, octahedral rough diamonds are highly desirable for diamond cutting and manufacturing.

Characteristics of an Octahedral Diamond
Crystal Structure: Composed of eight equilateral triangular faces
Formation: Forms naturally under high pressure and heat within the Earth’s mantle
Symmetry: Well-balanced, making it one of the most efficiently cuttable rough diamond shapes
Occurrence: One of the most common and valuable rough diamond shapes found in nature
Why Octahedral Rough Diamonds Are Coveted
1. Ideal for Cutting Round Brilliant Diamonds
The octahedral shape is perfectly suited for cutting two round brilliant diamonds from a single rough stone, maximizing yield and minimizing waste.
Diamond cutters often cleave or saw the rough along its natural planes to create two symmetrical, high-quality diamonds.
2. Natural Growth of Diamonds
The octahedron reflects the cubic crystal system of diamonds, where atoms arrange themselves in the most stable geometric form.
Over millions to billions of years, carbon atoms bond in this shape under extreme pressure deep within the Earth.
3. High Clarity Potential
Since octahedral diamonds grow in a stable environment, they often develop with fewer inclusions compared to irregularly shaped rough stones.
Their internal structure is generally strong, reducing the risk of fractures during the cutting process.
Octahedral Diamonds in Cutting & Polishing
How Cutters Assess an Octahedral Rough Diamond:
Orientation: Experts determine the best way to cut the rough to achieve the highest carat yield.
Inclusion Mapping: If internal flaws are present, cutters adjust the cutting plan to eliminate or minimize them.
Cleaving/Sawing: The rough is often split along its natural grain to form two high-quality gemstones.
Common Diamond Cuts from an Octahedron:
Cut Style Why It’s Chosen for Octahedral Rough
Round Brilliant Uses the natural symmetry of the octahedron to produce two symmetrical stones
Princess Cut Retains a high percentage of the original rough weight
Cushion Cut Maximizes brilliance while preserving rough material
Octahedron vs. Other Rough Diamond Shapes
Rough Diamond Shape Description Cutting Potential
Octahedron Eight triangular faces, symmetrical High yield, excellent for round brilliants
Dodecahedron Twelve pentagonal faces, irregular More cutting challenges, lower yield
Macles (Twinned Crystals) Flattened, triangular shape due to twinning Often used for fancy cuts, less efficient for rounds
Cubo-octahedron Mix of cube and octahedron faces Good for step cuts like emerald or Asscher

The octahedron is the most desirable natural shape for rough diamonds due to its symmetry, high clarity potential, and efficient cutting yield. This structure allows diamond cutters to maximize the rough’s potential, often yielding two high-quality round brilliant diamonds from a single octahedral crystal. Its formation represents the natural stability of diamond growth, making it a prized find in the world of gemology.

The term “off-make” is a trade term used to describe a diamond that has been poorly cut, polished, or finished, resulting in flaws in its overall make. This means the diamond does not meet ideal proportions, symmetry, or polish standards, leading to reduced brilliance, fire, and overall aesthetic appeal.

Characteristics of an Off-Make Diamond
A diamond is considered off-make when it exhibits one or more of the following defects:

1. Poor Proportions
Too deep or too shallow – Affects light reflection and reduces brilliance.
Mismatched angles – Poor crown and pavilion angles lead to light leakage.
Uneven girdle thickness – Some areas may be too thick (wasting carat weight) or too thin (making the diamond vulnerable to chipping).
2. Weak Symmetry
Misaligned facets – When facets are uneven or not placed correctly, the diamond lacks balance.
Table and culet off-center – Affects the diamond’s optical performance and sparkle.
3. Low-Quality Polish
Visible polish lines or marks – Can create a dull appearance.
Rough or grainy surface texture – Reduces light reflection and brilliance.
4. Light Performance Issues
Nailhead effect – The center appears dark due to excessive depth.
Fish-eye effect – A distorted reflection of the girdle inside the table, caused by a shallow pavilion.
Windowing – When light passes straight through the diamond rather than reflecting back, making it appear see-through.
How Off-Make Affects a Diamond’s Value
1. Lower Market Demand
Off-make diamonds are considered less desirable by both jewelers and consumers because they lack brilliance and symmetry.

2. Reduced Sparkle & Fire
A well-cut diamond maximizes brilliance (white light reflection) and fire (color dispersion).
Off-make diamonds often appear lifeless, dull, or dark, even with good clarity and color.
3. Lower Resale & Appraisal Value
Since cut is the most important factor in a diamond’s beauty, a poorly made diamond will be valued lower than a well-cut stone of the same carat weight, clarity, and color.
4. Potential for Weight Retention Over Beauty
Some off-make diamonds are intentionally cut poorly to retain more carat weight from the rough, sacrificing quality for size.
How to Avoid Buying an Off-Make Diamond
1. Check the Cut Grade
Buy diamonds certified by DCLA, GIA, or AGS, which provide cut grades ranging from Excellent to Poor. Avoid stones with Fair or Poor cut grades.
2. Inspect Light Performance
Look at the diamond under different lighting conditions to check for dark areas, weak reflections, or excessive transparency.
3. Look for Proportion Guidelines
Ideal Table Size: 53-58% of the total width
Ideal Depth Percentage: 58-63%
Crown and Pavilion Angles: Well-balanced for optimal light return
4. Use a Loupe or Microscope
Check for symmetry, facet alignment, and polish marks.
5. Ask for an ASET or Ideal Scope Image
These tools reveal light leakage, helping determine if the diamond is well-cut.

The Old Mine Cut is a historical diamond cut, first popularized in the 18th and 19th centuries. It is an early version of the modern cushion cut, characterized by its deep pavilion, high crown, small table, and large culet. These diamonds were hand-cut by artisans, making each one unique, with a softer, romantic appeal compared to today’s precision-cut stones.

Key Features of an Old Mine Cut Diamond
1. Cushion-Like Shape
The Old Mine Cut has a rounded-square or cushion-like outline, often with slightly asymmetrical edges due to hand-cutting techniques.
2. Deep Pavilion & High Crown
A deep pavilion (bottom part of the diamond) gives the stone a noticeable depth, which was designed to enhance light reflection in candlelight.
The high crown (upper portion of the diamond) contributes to its distinctive, antique look.
3. Small Table & Large Culet
The table (flat top facet) is relatively small, which contrasts with modern cuts that have larger tables to maximize brilliance.
The culet (bottom facet) is large and visible from the top, creating a soft reflection within the diamond instead of the sharp brilliance seen in modern cuts.
4. Fewer, Larger Facets
Typically features 58 facets, but they are larger and chunkier compared to modern brilliant-cut diamonds, producing a softer, less fiery sparkle.
5. Hand-Faceted & Slightly Asymmetrical
Old Mine Cuts were hand-faceted without modern precision technology, often leading to slight variations in shape and symmetry.
History of the Old Mine Cut
Originated in the late 17th to early 18th century and became the dominant diamond cut of the Georgian and Victorian eras.
Named “Old Mine Cut” because many of these diamonds came from old mines in Brazil and India, before major diamond discoveries in Africa.
With the invention of more advanced cutting tools, the Old European Cut (a rounder, more symmetrical version) evolved from the Old Mine Cut in the late 19th century.
How Old Mine Cut Diamonds Compare to Modern Cuts
Feature Old Mine Cut Modern Cushion Cut Round Brilliant Cut
Shape Cushion-like, slightly irregular Cushion-like, precise symmetry Perfectly round
Facets Large, chunky facets Smaller, precision-cut facets Tiny, uniform facets
Table Small Medium Large
Culet Large, visible Small or non-existent Very small or none
Brilliance Soft glow, optimized for candlelight Bright and fiery brilliance Maximum brilliance
Cutting Method Hand-faceted Machine-faceted Machine-faceted
Why Choose an Old Mine Cut Diamond?
1. Vintage & Unique Charm
Ideal for antique-style engagement rings or heirloom jewelry.
No two Old Mine Cut diamonds are exactly alike, adding to their individuality.
2. Warmer, Romantic Glow
Their soft sparkle creates a more romantic, vintage feel, different from the sharp brilliance of modern cuts.
3. Ethical & Sustainable Choice
Since many Old Mine Cut diamonds are reclaimed or antique stones, they offer a more environmentally friendly and ethical alternative to newly mined diamonds.
4. Great for Those Who Love History
Owning an Old Mine Cut diamond means having a piece of history from the Georgian, Victorian, or Edwardian era.

Features of an Oval Cut Diamond
1. Elongated Shape
The oval cut is an elongated shape that can range from a perfect oval to a more elongated ellipse depending on the ratio of length to width.
Proportions can vary, but a ratio of approximately 1.33 to 1.66 (length-to-width) is typically considered ideal for maintaining a graceful appearance.
2. Brilliant Cut Facets
Like the round brilliant cut, the oval cut diamond features 58 facets arranged in a brilliant cut style.
These facets are designed to maximize light reflection and create a stunning, fiery sparkle. The brilliance is typically comparable to that of round diamonds, though the oval shape tends to have a slightly softer light return due to the shape’s rounded edges.
3. Soft, Rounded Edges
Oval diamonds are characterized by their soft, rounded edges, making them less prone to visible chipping compared to shapes with sharp corners, such as the emerald cut or princess cut.
4. Larger Surface Area
The oval cut tends to appear larger than a round diamond of the same carat weight due to its elongated shape, offering more visual size, which is often appealing to those who prefer a larger stone without sacrificing carat weight.
5. Symmetry and Bowtie Effect
An important feature to check in an oval diamond is its symmetry. The diamond should have a balanced outline without any noticeable bulges or flat areas.
Many oval diamonds can exhibit a bowtie effect, where the center of the diamond appears darker, resembling the shape of a bowtie. While not a flaw, a noticeable bowtie can sometimes be distracting, so it’s important to select a stone with minimal or no bowtie effect.
Why Choose an Oval Cut Diamond?
1. Timeless Elegance with a Modern Twist
The oval cut has become increasingly popular due to its elegant, vintage charm, combined with a modern appearance. It offers the classic appeal of a round diamond but with a more distinctive and elongated look that feels fresh and different.
2. Appears Larger Than Other Shapes
Due to its elongated shape, an oval diamond can look larger than round diamonds of the same carat weight, offering more presence without the need to increase carat weight. This is especially appealing for those who want the look of a larger diamond at a more affordable price.
3. Versatility in Setting Styles
Oval cut diamonds pair well with various types of settings, including solitaire, halo, three-stone, and pavé bands. Their elongated shape can also flatter longer fingers, making them a popular choice for engagement rings.
The oval shape works well in both modern, minimalist settings and vintage-inspired designs, making it a versatile choice for any style preference.
4. Less Prone to Chipping
Since oval diamonds have no sharp corners like princess or emerald cuts, they are less susceptible to chipping or damage, making them a durable and practical choice for everyday wear, especially for engagement rings.
How to Choose the Perfect Oval Cut Diamond
1. Pay Attention to Proportions
Proportions are key when selecting an oval cut diamond. Look for a diamond with balanced length-to-width ratios (1.33 to 1.66) for a more elegant and symmetrical appearance.
Symmetry is also important to ensure the diamond’s facets align perfectly and create the desired visual appeal.
2. Check for the Bowtie Effect
The bowtie effect is a common characteristic of oval diamonds, but you may want to choose one with a minimal bowtie for better visual appeal. A pronounced bowtie can detract from the overall brilliance of the diamond.
3. Focus on the Cut Quality
The cut quality of an oval diamond significantly impacts its brilliance and sparkle. Ensure that the diamond has been cut to the highest standards, with well-executed facets that maximize light return. A well-cut oval will give the diamond brilliant sparkle similar to a round brilliant.
4. Opt for a Quality Certification
Choose a diamond with a certification from a reputable gemological laboratory, such as GIA, DCLA, or AGS. Certification ensures the diamond’s quality and gives you a detailed report on its cut, color, clarity, and carat weight.
Oval Cut vs. Other Diamond Shapes
Shape Unique Feature Brilliance Popular Setting Style
Oval Cut Elongated shape, large surface area Similar to round brilliance Solitaire, Halo, Three-Stone
Round Brilliant Perfectly symmetrical, circular Maximum brilliance Solitaire, Pavé, Halo
Cushion Cut Rounded corners, soft sparkle Moderate brilliance Halo, Vintage-Inspired, Solitaires
Princess Cut Square shape with sharp corners High brilliance, sharp sparkle Modern Solitaire, Three-Stone
Emerald Cut Step-cut with large, flat facets Subtle sparkle, elegant shine Solitaire, Vintage-Inspired

The Oval Cut diamond is a stunning choice for those who seek an elegant, elongated shape with exceptional brilliance. Combining the fire and brilliance of the round brilliant cut with a unique and flattering shape, it is a versatile option for various jewelry settings. The larger surface area and soft edges offer a distinctive look while being less prone to chipping. Whether you prefer a modern, minimalist design or a vintage-inspired setting, the oval cut is a timeless option that is sure to stand out.

The Effect of Strong Blue Fluorescence in Diamonds
The term “Overblue” refers to a diamond that exhibits strong blue fluorescence when exposed to long-wave ultraviolet (UV) light. This phenomenon occurs when the diamond absorbs UV light and emits a visible blue glow. While fluorescence in diamonds can be a natural and even desirable trait in some cases, an overblue diamond refers specifically to stones with extremely strong blue fluorescence, which can sometimes negatively impact their appearance.

Understanding Fluorescence in Diamonds
1. What is Fluorescence?
Fluorescence in diamonds is a natural occurrence that happens when a diamond absorbs ultraviolet light and then re-emits it as visible light, typically as a blue glow. Not all diamonds exhibit fluorescence, and its intensity can vary from none to very strong. Fluorescence is often graded on a scale from none to very strong, with the most common colors being blue (the most desirable) or less frequently yellow and green.

2. Types of Fluorescence
None: No fluorescence; the diamond remains unchanged under UV light.
Faint to Medium: Noticeable fluorescence, but usually doesn’t significantly impact the diamond’s appearance under normal lighting.
Strong to Very Strong: A bright, noticeable glow, which may be more obvious under UV light or in low-light conditions. In the case of overblue diamonds, this fluorescence is very intense and can affect the diamond’s overall appearance.
What Makes a Diamond Overblue?
An overblue diamond refers to a diamond with extremely strong blue fluorescence. This can result in a distinctive blue glow that may be evident under long-wave UV light or sometimes even in regular daylight. While fluorescence can enhance the diamond’s appearance in certain conditions, an overblue diamond can present issues for the stone’s overall aesthetic and value.

Issues with Overblue Diamonds
1. Oily or Milky Appearance in Daylight
Diamonds with strong fluorescence can appear cloudy, oily, or milky under normal daylight or incandescent lighting, which can affect their brilliance. This happens because the fluorescence can cause the diamond to scatter light unevenly, diminishing its overall sparkle.
High-color diamonds (D-F grades) with strong fluorescence are often the most affected, as their lack of color accentuates the milky or oily appearance.
2. Misleading Perception of Superior Colour
In the past, the term “overblue” was sometimes used to suggest that a diamond with strong blue fluorescence had a superior color grade, leading to confusion in the market. Some buyers believed that a strong blue fluorescence was an indicator of a higher-quality diamond.
However, fluorescence does not directly correlate with the color grade of a diamond, and a diamond’s appearance under normal lighting is far more important in assessing its true beauty.
3. Impact on Diamond Value
While some buyers find fluorescence attractive, an overblue diamond can decrease the diamond’s market value. This is because it affects the overall visual quality, particularly if the stone appears cloudy or oily under natural light.
Diamonds with extremely strong fluorescence can also be perceived as less desirable due to the unpredictable visual effects they may exhibit in different lighting environments.
Should You Avoid an Overblue Diamond?
Whether or not to buy an overblue diamond depends on your personal preferences and how the diamond appears to you in real-world lighting.

Reasons to Avoid an Overblue Diamond
Aesthetic Concerns: The milky or oily look that can appear under normal lighting may not appeal to everyone, especially those seeking a diamond with the highest possible brilliance and clarity.
Reduced Value: Overblue diamonds may be worth less in the market compared to their counterparts with less noticeable fluorescence.
Reasons to Consider an Overblue Diamond
Personal Preference: Some people enjoy the blue glow that fluorescence provides, especially under UV light.
Price: Due to the perceived lower value, diamonds with strong fluorescence may be available at a lower price, which could appeal to those on a budget.
How to Detect Overblue Fluorescence
If you’re interested in purchasing a diamond, it’s essential to check the fluorescence grading and assess how it might affect the diamond’s appearance.

1. Check the Diamond’s Certification
Reputable gemological laboratories like GIA, DCLA, and AGS will include a fluorescence grade on the diamond’s certificate. If the diamond is marked as strong blue or very strong blue, it may exhibit the overblue effect.

2. View the Diamond in Different Lighting
It’s essential to examine the diamond in natural light to see if the overblue fluorescence makes it appear cloudy or oily.
Examine the diamond under UV light to observe the fluorescence intensity and its effect on the stone’s visual appeal.
3. Personal Preference
Ultimately, whether to choose a diamond with strong fluorescence, including overblue, depends on your personal taste and the diamond’s appearance in various lighting conditions. If you are unsure, you may want to consult a gemologist or diamond expert to better understand how fluorescence will affect the look and value of the diamond.

Overblue diamonds exhibit extremely strong blue fluorescence, which can result in a distinct blue glow under UV light. In the past, the term was used misleadingly to suggest that the diamond had a superior color, but it can actually cause the diamond to appear milky or oily in normal daylight, especially for high-color diamonds. Fluorescence in diamonds is a natural phenomenon, but when it is too strong, it can detract from the diamond’s beauty. Whether you should buy an overblue diamond depends on your personal preference for the glow and how it looks in natural light. Be sure to check the fluorescence grading and view the diamond in different lighting before making a purchase decision.