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HOW TO READ YOUR DIAMOND GRADING REPORT

Knowing your way around a Diamond Grading Report is invaluable when selecting your diamond. 

We set out below a guide to reading a GIA and IGI report which includes an assessment of the 4Cs.

1.

HEAD OF THE REPORT 

This part tells you who graded the diamond. There are several institutions that grade diamonds and provide diamond grading report. The Gemological Institution of America (GIA) and the International Gemological Institute (IGI) are two of the most highly regarded diamond grading institutes. IGI, in particular, was the first gemological institute to fully grade lab-grown diamonds. 

2.

GIA OR IGI REPORT NUMBER

A distinct report number is assigned to each graded diamond. This number is registered in GIA's or IGI's database and is microscopically engraved on the girdle (the waist) of the diamond. 

With the GIA or IGI report number in hand, you can verify it here at the GIA website or the IGI website. 

3.

SHAPE AND CUTTING STYLE

This sets out the diamond shape and the pattern of the facet arrangement (cutting style).

To learn more about diamond shapes, check out our article here.

4.

MEASUREMENTS

The dimensions of the diamond are stated here. 

For round brilliant cut diamonds: this is set out as "minimum diameter - maximum diameter v depth". A minimum diameter and a maximum diameter is reported as diamonds (even well cut ones) are never perfectly round. 

For fancy-shaped diamonds: this is set out as "length x width x depth". 

5.

GRADING RESULTS (THE 4CS)

Here we have what is known as the 4Cs: 

  • Carat - the weight of the diamond given in carats, recorded to the nearest hundredth of a carat. (One carat is equal to 200 milligrams). 

  • Colour - this refers to the absence of colour. This is graded on a D (colourless) - to - Z (light) scale. (If “*” appears next to the colour grade, this means a colour treatment was detected.)

  • Clarity -- referring to the relative absence of inclusions (the internal characteristics) and blemishes (the external characteristics), this is graded on a scale from Flawless (FL) to Included (I) based on the size, nature, number, position, and relief of inclusions and blemishes visible under 10x magnification.

  • Cut - this grades the face-up appearance of the diamond (not to be confused with diamond shape). 

    • GIA grades cut on a scale of Excellent to Poor.

    • IGI grades cut on a scale of Ideal to Fair. 

Want to know more about the 4Cs? Learn more here.

6.

ADDITIONAL GRADING INFORMATION OR COMMENTS

  • Polish - this is the smoothness of the diamond's surface and is a sub-component of the overall cut grade. It is graded on a scale of Excellent to Poor.

  • Symmetry - this is the exactness of the diamond’s outline, and the shape, placement, and alignment of its facets. It is also a sub-component of the overall cut grade and is graded on a scale of Excellent to Poor.

  • Fluorescence - this is the strength and colour of the diamond when viewed under long-wave ultraviolet light. It is expressed on a scale from None to Very Strong.

  • Inscription: any inscriptions on the stone's girdle (its waist) will be noted here - this includes the GIA or the IGI report number.

  • Comments - any additional identifying characteristics or features that are not otherwise represented on the report would be set out here. For example, if a treatment is detected, such as laser drilling, it would be described here.

7.

PROPORTIONS

This is a graphic representation of the diamond's proportions. Proportions are a measurement of a stone's primary and secondary facets (the flat faces of the diamond). The proportions are expressed as average angles and percentages of the diamond's average girdle diameter.

8.

CLARITY CHARACTERISTICS

This is essentially a map of the diamond's internal and external clarity characteristics, as observed at 10X magnification. The most significant characteristic will generally be identified first. This may be useful to understand as an inclusion closer to the table (the flat top) of the diamond may be more visible than if it were closer to the pavilion (the pointy end) of

Different symbols indicate the type or nature, position, and the approximate size of a clarity characteristic.
 

9.

GRADING SCALES

Set out on the far right of the GIA or IGI report are their grading scales.

In respect of carity:

  • GIA grading scales range from Flawless (FL), Internally Flawless (IF), Very Very Slightly Included (VVS 1, VVS2), Very Slightly Included (VS1, VS2), Slightly Included (SI1, SI2) to Included (I1, I2, I3).

  • IGI grading scales range from Internally Flawless (IF), Very Very Slightly Included (VVS 1, VVS2), Very Slightly Included (VS1, VS2), Slightly Included (SI1, SI2) to Included (I1, I2, I3).

In respect of colour:

  • GIA's colour scale ranges from D to Z - which represent a grading range of Colourless to Light.   

  • IGI's colour scale ranges from D, E, F, G, H, I, J, Faint, Very Light, and Light.

In respect of cut: 

  • GIA's cut scale ratings are: Excellent, Very Good, Good, Fair, and Poor.

  • IGI's cut scale ratings are: Ideal, Excellent, Very Good, Good, and Fair.

10.

SHAPE AND CUTTING STYLE

This is a two-dimensional barcode that, when scanned, verifies data on the report against the GIA or IGI database. Other security codes include watermarks, microprinting and hologram. The IGI report also includes an enlarged photo of the diamond and a photo of the inscription on the girdle.

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