Diamond Valuation Guide


Diamond Valuation Guide

Find out how diamonds are valued in the resale market

At Auctentic we value hundreds of diamonds every week.

Each diamond is more than a billion years old and is unique, just like a fingerprint.

When people intend to buy a diamond, they try to find out first, to understand what makes them so valuable. It is important for you to do the same before selling your diamond and it is important for us too, because we want you to be able to trust Auctentic with confidence and understand in the clearest and most transparent way the level of service and how much the offer you receive is fair and in agreement with the resale market. Below you can read the guide that helps you to sell your diamonds, following the same steps as our specialists to identify the stones and evaluate them.

1. Identify shape and cut

The shape of the diamond is a very important factor in giving it a value. Round brilliant cut diamonds tend to have a higher valuation than more unusual cuts. With Auctentic, a diamond with an excellent cut is paid up to 30% more: the evaluation system is the one established by the GIA for the quality of the cut, which is also the one taken as a reference by our international buyers.

ideal diamonds cut chart 

Are all round brilliant cuts perfectly round?

The truth is that many of the diamonds we evaluate live in Auctentic's offices have not been cut with the technology and precision available to today's cutters. This means that we are often faced with diamonds that are not perfectly round, with the diamond table not centered and non-symmetrical facets. Reselling these not-fully-round diamonds may require a cut.

2. Valuation of the diamond

Although they have been worn several times, since diamonds are the hardest material known to man (see Mohs scale), they are usually in excellent condition. However, sometimes this is not the case: diamonds have four directions in which they can easily split and cutters use this property to cut them. It can happen that the diamond is damaged during mounting on a jewel because sometimes this operation can put a lot of pressure on the stone. Unfortunately, just a tap in the wrong place is enough to chip a diamond: this can happen more easily in the corners of a Princess cut or in the culet, which is the point at the base of the diamond. If the diamond that arrives at our offices is damaged, our specialists will need to calculate how much weight will be lost during the cutting operation to bring the diamond to perfect proportions and quote it accordingly.

chipped diamonds examples 

Auctentic helps you to sell chipped diamonds too, you just need to honestly declare the condition of your stone documenting it with clear and exhaustive photos of the affected lesion(s).

Send us the photos of your chipped diamond to sell it immediately, by filling out the form by clicking here.

3. Valuation of the diamond weight

Most of the diamonds we receive are set on jewelry. We estimate the weight of the diamond by measuring its diameter and depth down to the millimeter with the aid of various tools that use mathematical formulas to calculate the estimated weight of the stone very accurately.

Diamond prices are based on weight and it is important to know that these prices jump up in certain weight ranges. For example, between 0.99 ct G SI1 and 1.00 ct G SI1 the price difference can easily exceed €1100. As it is very unlikely that a cutter will cut diamond to 0.99 ct, it is usually preferred to compromise on the cut of the stone to keep the higher weight intact.

Removing a diamond from a ring 

In case the Auctentic experts estimate the weight of your diamond at 0.99 carats, we would ask you for permission to remove the stone from its setting to weigh it, to guarantee you the best possible price from our buyers.

4. Clarity Grading

Our gemologists are trained to valuate diamonds according to the quality standards set by the GIA, to guarantee you the best valuation and the best deal.

The GIA is one of the most respected diamond certification laboratories in the entire jewelry industry and its standards are internationally recognized.

Most of the diamonds sold with Auctentic at auction and direct bids are already GIA certified or are sent for certification by the GIA before going to auction.

What is the diamond clarity grading?

When classifying the clarity of a diamond, the gemologist checks for inclusions (or imperfections) both on the surface and inside the diamond itself.

Inclusions are particles that were trapped in the diamond at the time it was forming millions of years ago. Each diamond and its inclusions are unique, like a fingerprint, and prove that the stone is natural and not man-made. The clarity grading is carried out using a 10x magnifying glass, to check for even the slightest inclusion within the diamond and any imperfections on the surface. There are different types of inclusions and if your diamond is certified, you can find them described and even rendered graphically, so whoever valuate your stone will be able to clearly know where to look for them in the report or certificate.

Find out what they are called and what are the main diamond inclusions

Diamond inclusions 

Our gemologists carefully and accurately evaluate your diamond and then assign it one of the 11 clarity grades of the GIA standard, which are:

Flawless (FL) - (Perfect, no inclusions) There are no inclusions or imperfections visible to an experienced gemologist using a 10x magnifying glass.

Internally Flawless – (IF) - At the 10x magnifying glass used by an expert gemologist no inclusions are visible but only imperfections.

Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult to see even for an experienced gemologist under a 10x magnifying glass.

Very Slightly Included (VS1 and VS2) - The inclusions present are unimportant and can be difficult or fairly easy to identify to the eye of an expert gemologist under a 10x magnification lens.

Slightly Included (SI1 and SI2) - Inclusions are visible to an experienced gemologist using a 10x magnifying glass.

Included (I1, I2, and I3) - Inclusions are evident at the 10x magnifying glass and have negative effects on the transparency and brilliance of the diamond.

5. Checking the girdle

The girdle (in the international terminology of the diamond industry), is the dividing line between the top (crown) and bottom (pavilion) of the stone that helps protect the diamond from chipping.

The gemologist checks the condition of the girdle after having classified the clarity of the stone, checking its thickness, status and whether there are any laser inscriptions along it.

Girdle elements

Thickness - A girdle that is too thick affects the beauty of the stone and may also affect our specialists' estimation of its weight, because it makes it look smaller than it is. The girdle is there to protect the diamond and therefore it should be thick enough to prevent chipping but not so thick as to look unsightly. The thickness value is expressed as a percentage because it can be thin on one side and thicker on the other. The GIA uses an 8 degree scale to classify girdle thickness:

  • Extremely Thin
  • Very thin
  • Thin
  • Medium
  • Slightly thick
  • Thick
  • Very Thick
  • Extremely Thick

diamond girdles chart 

Girdle finishes

Diamond girdle are finished in 2 ways:

Rough – this is the natural state of the rough diamond, so the girdle has not been altered during the cutting and polishing process and has a tarnished, frosted appearance.

Faceted - when the diamond was polished, the girdle was also polished to make it shine.

Laser inscription

examples of girdle's laser inscription on a diamond 

Upon request, the gemological laboratories also offer a laser inscription service on the diamond girdle, where they place a small logo and the certificate number, without affecting the clarity of the stone: anyone examining the diamond later, will thus be able to trace the diamond report, thus gaining access to all the stone's characteristics. It is also possible to have messages engraved on the girdle, which can be removed before the diamond is resold.

6. Checking treatments

A treated diamond is one that has been altered in its appearance, usually to improve color or clarity, if not both.

Treatments always affect the value of the diamond. Lasers or treatments can be used to fill the fractures in diamonds: the downside the downside is that the price of the treated diamond drops by half compared to an untreated natural diamond.

There are several treatments that can be carried out on a diamond and most of these are easily detected by experienced gemologists using a magnifying glass. Two of the most common treatments we come across are laser treatment and small fracture filling.

Laser Drilling

The laser drilling method is carried out on a diamond that has dark inclusions in it. Through a laser beam of the size of hundredths of a millimeter, the diamond is drilled until the inclusion is reached, which is then lightened with an acid solution (and remains distinguishable). The channel created by the laser is then filled in, but is still visible. It is clear that the closer the inclusion is to the surface of the diamond, the more effective the method is. The laser method is applied to diamonds with a low clarity grade and if the procedure is carried out correctly, it can increase the clarity scale by one or two degrees but not more.

example of laser drilling on a diamond before and after 

Fracture Filling - Infiltration and Filling of Fractures

The method of infiltrating and filling fractures with high refractive index materials was patented in 1982 by Zvy Yehuda. It applies to diamonds with a low grade of clarity and with indentations on the surface. Glass compounds penetrate the fracture and improve the clarity of the stone. In order to allow the identification of the treatment, a dye is added to the filling compound. Also in this case, an expert gemologist can easily recognize the treatment undergone by the diamond.

Fracture filling, before and after 

7. Color Grading

The international color scale, created by the GIA, begins with the letter D (which is the whitest color) and ends with Z (which is the yellowest color). Beyond this color scale there are diamonds from the fancy range, which outlines colored diamonds, which can be yellow, pink, blue, green, red, orange and brown.

Diamonds clarity chart 

Checking a loose diamond, that is, not mounted on a jewel, is the most accurate way to classify the color, which requires the practice of a highly experienced gemologist.

The letters D, E, F, G, identify collection or investment diamonds, while H, I and J represent most of those used in jewelry.

Diamonds color table 

When we receive your diamond mounted into a piece of jewelry, if it needs to be removed we ask for your permission first, in order to classify the color as accurately as possible. In fact, to establish the true color of the diamond, the stone must always be turned upside down and not simply observed from above (as happens if the stone is set), as reflections interfere with human sight, effectively preventing an accurate color classification. It is therefore impossible to establish the real color of the diamond when it is mounted into a piece of jewelry, for several reasons, among which: the color of the metal, which interferes with the appearance of the stone and some types of settings that surround the entire diamond preventing the light from passing through completely.

Master stones for diamond color grading

Master Stones 

Master stones are the most used method for evaluating the color of diamonds. Usually a minimum of 9 stones are used, which correspond to the color degrees from the letter D to the letter L. The gemologist compares the stone to be classified with the master stones, placed on a white background with the table facing down. Even the diamond to be evaluated is turned upside down for comparison and to be able to determine its color in relation to the master stones. The color is assigned when an ideal match is found between the color of one of the master stones and that of the diamond under examination.

8. Checking for fluorescence

Let's start by saying that the best diamonds must not have fluorescence. Fortunately, very few diamonds have fluorescence that can affect their appearance. Fluorescence is a sparkle emanating from the diamond in the presence of long ultraviolet waves (such as daylight). Usually, this sparkle is blue, but yellow, orange, green and other colors of fluorescence can also be found.

Intensity grades of diamond fluorescence

There are four degrees of fluorescence, depending on the intensity of the light emitted by the diamond, compared to the master stones in the laboratory:

  • None or Nil
  • Faint (Weak)
  • Medium
  • Strong
  • Very Strong

Diamond fluorescence  

Usually, most of the fluorescences do not affect the appearance of the diamond but in the Strong and Very Strong grades they can make the stone appear cloudy. And a bluish fluorescence can make a pale yellow diamond appear whiter under UV light, such as daylight: the result of this effect can raise its price per carat compared to similar diamonds without fluorescence. On the other hand, a D-color diamond may appear to be tarnished by the same fluorescence and have a negative effect on its price, dropping it by up to 25%.

9. Checking the metal

The weight of jewels is measured in grams and the weight of diamonds and other precious stones is deduced from the initial weight. The metal is tested to determine its quality, although in some cases there are international acronyms engraved on the metal that guarantee its characteristics. The metal is tested in different ways, such as by removing a tiny particle on which a drop of acid is applied as an indicator of the type of metal. The price of precious metals varies daily and the price paid per gram corresponds to that of the valuation day.

If you have read this far, then the picture is quite clear to you: to have your diamonds valued you must rely on expert hands, such as our team of gemologists at Auctentic, who guarantee you impartiality and professionalism in highlighting the strengths and weaknesses of your stone and giving you the best price on the resale market.


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