The Grading Process

Natural diamond grading at Naturalmark Lab Pvt. Ltd. follows a systematic process based on the 4Cs (Carat, Cut, Color, and Clarity), along with additional evaluations for authenticity and other characteristics. Here’s a step-by-step breakdown:

Pre-Grading Examination

Cleaning the Diamond: The diamond is cleaned to remove any dust, oil, or residue that may affect grading.

Initial Inspection: The diamond is examined under magnification to check for surface features, inclusions, and fluorescence.

Identification: Screening machine & Advanced instruments (e.g., spectrometers, microscopes) are used to confirm whether the diamond is natural, natural treated ( HPHT ), Labgrown or synthetic.

Carat Weight Measurement :

The diamond is weighed using a precise electronic balance.

Color Grading

The diamond is compared to master stones under controlled lighting. Color is graded on a scale from D (colorless) to Z (light yellow or brown). Fluorescence is also checked under UV light.

Clarity Grading

The diamond is examined under a 10x magnification microscope. Inclusions (internal) and blemishes (external) are identified and mapped. Clarity is graded from FL (Flawless) to I3 (Included).

1. FL (Flawless): No inclusions or blemishes under 10x magnification.

2. IF (Internally Flawless): No internal flaws; only minor surface blemishes under 10x magnification.

3. VVS1/VVS2 (Very Very Slightly Included): Minute inclusions that are extremely difficult to see under 10x magnification.

4. VS1/VS2 (Very Slightly Included): Minor inclusions that are somewhat easy to see under 10x magnification.

5. SI1/SI2 (Slightly Included): Noticeable inclusions under 10x magnification but not easily visible to the naked eye.

6. I1/I2/I3 (Included): Obvious inclusions under 10x magnification, often visible to the naked eye, and may affect durability.

Cut Grading

The proportions, symmetry, and polish of the diamond are analyzed. Parameters such as table percentage, crown angle, pavilion depth, and girdle thickness are measured. The overall cut grade (from Excellent to Poor) is determined based on light performance.

Additional Tests

Fluorescence Analysis: Determines if the diamond emits light under UV exposure.

Optical Properties: Checked using spectrometers to confirm natural origin.

Inclusion Plotting: A clarity diagram is created for documentation.

Report Generation

The final grading report includes details on 4Cs, fluorescence, symmetry, polish, proportions, and a clarity plot. The diamond may also receive a laser inscription on the girdle for identification.

Quality Assurance & Final Verification

A senior gemologist cross-checks the grading to ensure accuracy and consistency. The diamond is securely packaged, and the grading report is issued to the client. This systematic process ensures accurate and reliable grading of natural diamonds in a Naturalmark Lab.

The Naturalmark diamond grading report covers following aspects of grading.

In order to distinguish Natural & Labgrown diamonds, Naturalmark Lab Pvt. Ltd. has seperate brand Labgrownmark for Labgrown diamonds.

Lab-grown diamonds are graded using the same 4Cs (Carat, Cut, Color, and Clarity) as natural diamonds. However, additional steps are required to identify their synthetic origin and growth method (HPHT or CVD). Below is a step-by-step grading process in a laboratory:

Identification & Initial Examination : Before grading, it is essential to confirm whether the diamond is lab-grown or natural.

Cleaning & Preliminary Check : The diamond is cleaned to remove dust and oil. A gemologist examines the stone under magnification to check for synthetic growth features like metallic inclusions (HPHT) or striation lines (CVD).

Screening & Advanced Identification Tests : 

UV-Vis Spectroscopy detects color centers unique to lab-grown diamonds.

FTIR Spectroscopy: Confirms the diamond’s chemical composition.

Photoluminescence Spectroscopy: Identifies growth method (HPHT or CVD).

Cross-Polarized Light Test: Checks for strain patterns (lab-grown diamonds show uniform strain).

Carat Weight Measurement : The diamond is weighed on a precision electronic scale with 0.001 carat accuracy.

Color Grading : The diamond is compared against master stones under controlled lighting.

Graded on the D-Z scale.

Special Considerations: HPHT Grown diamonds may have a bluish or yellowish tint while CVD-grown diamonds may have brownish undertones due to nitrogen impurities.

Fluorescence Test: Many lab-grown diamonds exhibit strong fluorescence under UV light.

Clarity Grading : Examined under 10x magnification using a gemological microscope.

Common inclusions in lab-grown diamonds:

HPHT diamonds: Metallic flux inclusions, tiny black specks.

CVD diamonds: Striation lines, pinpoints, or cloud-like inclusions.

Clarity grading : It is graded from FL (Flawless) to I3 (Included).

Cut Grading : Proportions, symmetry, and polish are analyzed using optical measurement tools.

Key parameters measured:

1. Table percentage
2. Depth percentage
3. Crown and pavilion angles
4. Girdle thickness

Overall cut grade: Ranges from Excellent to Poor, based on light performance.

Additional Tests & Laser Inscription

Spectroscopic Analysis: Confirms the diamond’s synthetic origin and growth method.

Inclusion Plotting: A clarity diagram is created.

Laser Inscription (if applicable):

Naturalmark Lab Pvt. Ltd  inscribes “Labgrownmark” and the report number on the girdle.

Certification & Final Report : A grading report is issued, containing:

4Cs details (Carat, Cut, Color, Clarity), Fluorescence information, Lab-Grown Diamond classification and Growth method (HPHT or CVD)

Final Verification & Quality Control

A senior gemologist reviews the grading to ensure consistency. The Lab grown diamond is securely packaged with the certificate.

Key Differences from Natural Diamond Grading

1. Identification is crucial to distinguish lab-grown from natural diamonds.

2. Growth method (HPHT or CVD) is recorded in the report.

3. Laser inscription is often mandatory for transparency.

Grading diamond-studded jewelry in a Naturalmark Lab Pvt. Ltd. involves assessing several factors to determine the color & clarity quality of the diamonds and the metal setting. Here’s a step-by-step guide to grading such jewelry:

1. Preparation and Cleaning Cleaning: Use ultrasonic cleaners or steam cleaners to remove dirt and oils. Inspection: Check for any loose stones or damage to the setting.
2. Diamond Authentication We use gemological tools like a screening machine, refractometer and spectroscope to confirm diamond authenticity and identify potential simulants or synthetic stones. If any piece is found apart from natural diamonds, it will be marked red by a marker pen & returned to replace it with natural diamond. If any piece is found natural treated/drilled/HPHT diamond, it will be marked black by a marker pen & returned to replace it with natural diamond.
3. Initial Inspection Visual Assessment: Use a loupe (10x magnification) or microscope to examine the jewelry. Documentation: Cross check the details submitted
4. Diamond Grading (4Cs) Gross Weight: Weigh the entire piece first. Carat Weight : If there is any doubt on diamond's carat weight mentioned on requisition slip, Gemologist measure individual stones if possible or estimate weight based on dimensions. Color Grading: Use a white background and controlled lighting. Compare with studded master stones to determine the diamond color grade Clarity Grading: Examine under 10x magnification for inclusions and blemishes. Cut Grading: Evaluate the diamond’s proportions, symmetry, and polish. Assess how well the diamond reflects light (brilliance and fire).Milky stones or weak brilliance diamonds affects clarity grade. Though, Naturalmatk Lab doesn't mention Cut grade in a report. Metal Grading
   • Metal Purity : Hallmarks and Stamps: Check for manufacturer marks and metal quality stamps.
5. Setting and Craftsmanship Evaluation : Inspect how securely and evenly the stones are set. Evaluate craftsmanship quality and symmetry in design.
6. Certification and Documentation :
   • Prepare a mini grading report including diamond characteristics, metal quality if Hallmarked, and a nicely clicked photograph and any relevant remarks.
7. Quality Assurance and Final Inspection : Double-check all data and observations. Ensure consistency with laboratory standards and procedures.

Diamond Screening Process

All screened diamonds identified as natural are sealed in tamper-proof packets. If any diamonds are found to be other than natural mined diamonds (e.g., lab-grown or synthetic stones), they are separated and placed in a red color labeled packet alongside the natural diamond packet. This ensures proper screening and segregation.

In certain cases, a few diamonds may be placed in a "Refer for Further Testing (RFT)" packet. These require additional analysis using a separate machine to determine possible treatments or to verify if they are natural Type IIa diamonds.

Screening Steps:

1. Weighment (Initial):
   Customers are requested to weigh their packet in the presence of the gemologist before submission.
2. Cleaning:
   All diamonds are cleaned prior to the screening process.
3. Screening:
   Diamonds are screened using advanced technology machines.
4. Segregation: If any lab-grown or synthetic stones (e.g., Moissanite or Cubic Zirconia/A.D.) are detected, they are separated and placed in a clearly labeled packet.
5. Refer to further Test (R.F.T.) Diamonds that cannot be detected using screening machines and require further analysis are placed in the RFT packet for advanced testing.
6. Weighment (Final):
   After screening and segregation, diamonds are re-weighed by the customer to confirm the receipt and accuracy of the process.
7. Non-Tearable Packaging: Natural diamonds are returned in the original packet provided by the customer. Any non-natural diamonds are returned in a separate packet labeled in red color. All packets are sealed together in a single non-tearable recycled plastic bag to ensure accuracy, security and transparency.

Naturalmark Lab issues report for screening, if required by a customer.

Identifying natural rough diamonds at Naturalmark Lab requires a systematic approach using both visual inspection and advanced analytical techniques.

1. Preliminary Examination

Cleaning: Clean the rough diamond thoroughly to remove dirt and debris using ultrasonic or steam cleaning.

Visual Inspection: Use a 10x loupe or microscope to inspect the crystal shape, surface features, and inclusions.

Documentation: Record the size, shape, color, and any noticeable features.

2. Physical Inspection

Crystal Habit: Check for common diamond crystal forms such as octahedrons, dodecahedrons, or cubes.

Surface Features: Look for Triangular growth patterns (trigons) on the surface, Natural etchings or dissolution marks and distinctive grain lines or striations.

Transparency and Luster: Natural rough diamonds typically exhibit a greasy or adamantine luster.

Hardness Test: Scratch the sample using a corundum (hardness of 9) to verify diamond's hardness (10 on the Mohs scale).

3. Optical and Gemological Testing

Refractive Index (RI) Test: Use a refractometer to check the RI (diamond: 2.42).

Polariscope Test: Confirm singly refractive nature (diamonds are singly refractive, while many simulants are doubly refractive).

UV Fluorescence: Examine under short-wave and long-wave UV light for fluorescence patterns. Natural diamonds may show blue, yellow, or green fluorescence.

4. Screening & Advanced Spectroscopic Analysis

Raman Spectroscopy: Identifies carbon structure; diamonds exhibit a characteristic peak at around 1332 cm⁻¹.

Fourier-Transform Infrared Spectroscopy (FTIR): Detects impurities and distinguishes between natural and synthetic diamonds.

Photoluminescence (PL) Spectroscopy: Helps identify treatments and synthetic origins

5.Identification of Inclusions and Internal Characteristics

Microscopic Examination: Observe natural inclusions like mineral crystals, growth lines, and clouds.

6. Verification and Certification

Comparison with Database: We match results with reference data from gemological databases.

Expert Verification: We have trained gemologists and certified expert verify the findings.

Report Generation: After identifying the stone/stones, we generate a mini report with findings, methods used in rare cases and remarks.