Diamond Guide


Whether you’re looking online or on the high street, our diamond guide will help you to understand diamonds better – helping you make an informed choice.

To start with, all diamonds are appraised using the 4 C’s (Clarity, Carat, Cut & Colour), and depending upon how good or bad each element of the 4 C’s is will determine the stones appearance, desirability and price.

We have broken down each of the 4 C’s below:


Diamond Clarity is the term relating how many imperfections a stone may have.

Imperfections found within a diamond are called inclusions, whereas imperfections found outside of the stone are known as blemishes.

A typical inclusion would be tiny crystals, trapped within the diamond as it forms (which happens under extreme heat and pressure). Blemishes occur after the stone has been created, (effectively man made damage) and could be damage such as a chipped edge or scratched surface.

When valuing a diamond it is most desirable to have a stone free of any inclusions and blemishes (although this is very rare), however most stones will have inclusions to some degree. It is possible to have a diamond with small inclusions which are invisible to the human eye, these grades are listed below and offer the balance of a clean looking stone at a good price.

Diamond clarity is graded using a jewellers loupe (magnifying glass with a 10 times zoom), and the various degrees of clarity are graded as per the scale below:

  • IF - absolutely free from inclusions, no imperfections visible through a 10x loupe.
  • VVS 1/2 - very very small inclusions, nearly invisible through a 10x loupe.
  • VS 1/2 - very small inclusions, barely visible through a 10x loupe.
  • SI 1/2 - small inclusions visible through a 10x loupe but invisible to the naked eye.
  • I1 - inclusions immediately evident with a 10x loupe though hard to see with the naked eye.
  • I2 - large/numerous inclusions visible to the naked eye and affecting brilliance.
  • I3 - large/numerous inclusions very visible to the naked eye and affecting brilliance.

At Hathaway Styles we only use diamonds that have a minimum diamond clarity of SI1.


Diamond carat is the unit of weight used for measuring how much a diamond weighs. One metric carat weighs exactly 200mg (milligrams).

The carat of a diamond is used to verify the exact weight of a diamond it is not used to determine a diamonds size. Therefore a two carat diamond is twice the weight of a one carat diamond, not twice the size.

Some jewellery is made up with more than one diamond and jewellery of this sort will have a total diamond weight. A total diamond weight simply equates to the total weight of all diamonds used in a piece of jewellery. A total diamond weight is not as valuable as the equivalent individual diamond weight.

Bigger diamonds have bigger prices, as the size of a diamond increases so does the rarity and cost. A two carat diamond is approximately four times the price of a one carat diamond of equal quality.

In order to give you an idea of what size a diamond is for a particular carat weight we have converted diamond carat weights into their approximate sizes in millimetres below.

Brilliant Cut Diamonds

  • 0.30 Carat = 4.40 mm
  • 0.40 Carat = 4.70 mm
  • 0.50 Carat = 5.10 mm
  • 0.70 Carat = 5.60 mm
  • 0.80 Carat = 5.90 mm
  • 0.90 Carat = 6.20 mm
  • 1.00 Carat = 6.50 mm
  • 1.20 Carat = 6.75 mm

Princess Cut Diamonds

  • 0.30 Carat = 3.80 mm
  • 0.40 Carat = 4.00 mm
  • 0.50 Carat = 4.40 mm
  • 0.70 Carat = 4.90 mm
  • 0.80 Carat = 5.20 mm
  • 0.90 Carat = 5.35 mm
  • 1.00 Carat = 5.55 mm
  • 1.20 Carat = 5.95 mm


Diamond cut is used to determine two things about a diamond.

Firstly diamond cut relates to the proportions, symmetry and polish of a diamond. These are the main factors which determine how well a diamond will sparkle and look aesthetically, other than the shape. A well cut diamond is often achieved at the expense of losing some of the diamonds weight, which is why bigger isn't always best.

Secondly, diamond cut is also a generalised term referring to the shape of the stone e.g. round (brilliant cut), square (princess cut) etc.

To express the overall cut/make of a diamond there is a scale of qualities ranging from excellent to poor:

  • Excellent – The finest grade of cut. Diamonds will display the maximum amount of light and display Brightness, Fire and Scintillation.
  • Very Good – Marginally darker appearance to an excellent cut, but overall a very similar appearance.
  • Good – Darker appearance with less scintillation than an excellent cut.
  • Fair – A general dark appearance with poor contrast.
  • Poor – Very dark appearance, combined with bad proportions.

The symmetry of a diamond is how well aligned the facets of the diamond are. The main contributing factor in how well a diamond sparkles is how the light travels through the diamond. The light should enter the diamond and be reflected out at the top towards the person looking at it, not out of the side or downwards as a poorly cut diamond would.

The polish of a diamond is how smooth or rough the facets are. A poorly cut diamond will have rough and jagged facets, whereas a well cut diamond will have smooth facets that will similar to a well-polished car have real depth and shine.


Diamond colour is based upon a standardised scale set by The Gemmological Institute of America. Every gemmologist carries a set of master stones which means they can compare diamonds to determine a diamonds colour, this process is always performed under strict lighting conditions.

GIA’s diamond colour grading scale:

  • Colourless - D, E, F
  • Near Colourless - G, H, I, J
  • Faint - K, L, M
  • Very Light - N, O, P, Q, R
  • Light - S, T, U, V, W, X, Y, Z

The rarest and most expensive of diamonds are the colourless ones, with diamonds becoming less expensive as the tint of colour increases. Diamonds above a colour H on the scale gradually become more tinted yellow in appearance.

A diamonds colour can also be affected by surrounding surfaces this is why a diamond is always graded for colour under strict lighting conditions.

Certified Diamonds

With larger more valuable stones (typically 0.30 carat and above) it is advisable to make sure the stone has been independently certified, which ensures the diamond will be the quality that it’s being sold as. There are various diamond grading laboratories around the world, but the most respected ones are GIA, IGI and HRD.

A diamond certificate or dossier will tell you the following information about a stone:

  • Shape
  • Measurements (mm)
  • Proportions (%)
  • Weight (carats)
  • Colour
  • Clarity
  • Fluorescence (if present)
  • Details of the Finish (e.g. Symmetry & Polish Grades, Girdle Depths)
  • Overall Cut Grade (round stones only)
  • Enhancement Details (if any)

Conflict Diamonds

We only select diamonds that are ethically sourced and free from worldwide conflict.

SafeGuard Jewellery Assessment

For additional peace of mind when purchasing stone set rings from us, we can also offer a SafeGuard Jewellery Assessment Report. The report is an independent expert assessment carried out by SafeGuard, who are part of the Birmingham Assay Office.

The report is an overall description of the ring, but also includes:

  • Diamond Quality
  • Diamond Sizes and Gross Weights
  • Precious Metal Type
  • Digital Photograph of Ring
  • Individually Hologrammed Booklet 

The standard timescale for a Jewellery Assessment is approximately 1 week, although an express service is also available.

We cannot offer a refund on Jewellery Assessments, however we are happy to send your jewellery for appraisal after you have tried it first.

Please note: The SafeGuard Jewellery Assessment is not a valuation service, for Independent Valuations we use SafeGuard Valuations.