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Education

What Are Diamond Cut Grades? Why Cut Is the Most Important C

What Are Diamond Cut Grades? Why Cut Is the Most Important C

Of the four Cs, cut, colour, clarity and carat, cut is the one that most directly determines how a diamond looks to the naked eye. It's also the one buyers understand least. Here's a full breakdown.

What "cut" means

Diamond cut doesn't refer to the shape, round or oval or emerald. It refers to how well a diamond has been cut from the rough crystal: the proportions, symmetry and polish of the facets, the flat angled surfaces that catch and reflect light.

A well-cut diamond takes in light through the table, the top surface, bounces it internally between the facets, and returns it to your eye as brilliance (white light), fire (coloured flashes) and scintillation (the twinkling as the diamond moves). A poorly cut diamond loses that light through the bottom or sides and looks dull, even with excellent colour and clarity.

How cuts are graded

For round brilliant cut diamonds, GIA and IGI both provide a cut grade: Excellent, Very Good, Good, Fair or Poor. Excellent means the proportions are optimised to maximise light return. For fancy shapes such as oval, emerald and pear, there's no standardised cut grade, which is why buying from a jeweller with expertise in selecting fancy shapes matters.

Why cut matters more than colour or clarity

A G-colour, VS2-clarity diamond with an Excellent cut will outperform a D-colour, IF-clarity diamond with a Poor cut in every visual way. Cut is what makes a diamond look alive.

Many buyers spend their budget chasing higher colour or clarity grades without realising a well-cut stone with slightly lower grades will look brighter in person.

What to look for when buying

For round brilliants, aim for Excellent or Very Good cut. For fancy shapes, ask your jeweller about the specific length-to-width ratio, depth percentage and table percentage. Those determine the stone's face-up appearance. Avoid stones with overly deep or shallow depth percentages, which indicate light loss.

At Una Diamond we select each stone individually. Get in touch if you want guidance on choosing the right diamond for your budget, or explore our full range of engagement rings.

See Cut Grades in Practice at Una Diamond

Centre stones of one carat and up are IGI certified with a specified cut grade. Browse our collection: