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Diamond Quality Demystified, Our 10 Point Test

At Guthrie’s we’re a little obsessed with diamond quality, it has been a key focus of our company for our 50-year history to source only the best globally.

But what makes a quality diamond? A quality diamond display’s a unique and particularly beautiful character. Because of this, we developed our 10 point test, a set of strict standards to ensure we only present the very best to you.

This is something of which it pays to know before buying an engagement ring, or item of fine jewellery. We’ve outlined this 10 point test for you below.

Diamond Cut Grade

1. Excellent Cut

The cut is crucial to a diamond’s fire and brilliance – the technical terms for sparkle and shine. We only accept the highest grade possible, Excellent in Rounds and Excellent or Very Good in Fancy Shapes.

Diamond Symmetry Grade

2. Excellent Symmetry

Not all diamonds are cut symmetrically, while not obvious at first the best way to ruin a beautiful cut grade is with poor symmetry, We only accept Excellent in Rounds and Excellent or Very Good in Fancy Shapes.

Diamond Quality - Polish Grade Explained

3. Excellent Polish

A diamonds polish grade is the quality of the outside surface, this can range from diamond to diamond due to the cutting process. We only accept Excellent in Rounds and Excellent or Very Good in Fancy Shapes.

Diamond Colour Grading Example

4. Colourless

We only accept diamonds in the colourless or near colourless bracket. Both of these brackets will result in the diamond either being completely white or an undetectable amount of colour.

Ensuring an Eye Clean Diamond

5. Eye Clean

Inclusions are tiny impurities that become trapped inside a diamond as it is being formed. Inclusions range from minute imperfections to large visible marks inside the diamond. All of Guthrie’s Diamonds are free from visible inclusions.

Diamond Quality - No Brown, Green or Milky Inclusions

4. No Brown, Green or Milky Inclusions

Not all inclusions are created equally, some might say; a nice inclusions is like a freckle, whereas a bad inclusion is definitely a blemish. We don’t supply diamonds that have brown, green or milky inclusions.

Fluorescence Explained

7. No Fluorescence or Blue Fluorescence.

Fluorescence is the colour the diamond returns to the viewer when light is refracted through it. We only supply diamonds that have a nice blue fluorescence or none at all. Other colours of fluorescence such as yellow, green or red we don’t supply.

Diamond Girdle Explained

8. Not Prone to Chipping

Diamonds with a girdle that is too thin are at risk of chipping, diamonds that have a girdle that is too thick lose size for weight. A medium-thick girdle is the highest grade and what we supply.

GIA Certification

9. GIA Certified

GIA or the Gemological Institue of America is the worlds foremost authority in Gemology, this company actually invested the 4 C’s, All of Guthrie’s Diamonds are GIA Certified. You can visit GIA’s website here –

10. Ethically Sourced

At Guthrie’s we take our commitment to Ethical Sourcing Seriously, all of our diamonds are not only sourced from reputable suppliers but have a transparent history from mine to consumer.

Further information

For further information on diamonds, including pricing we would recommend downloading our informative guide here.

About the Author

James, a third generation member of the jewellery industry spent a huge amount of time around the industry from a young age. With a passion for beautiful diamonds and gemstones and an eye for quality design.

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