Understanding your UGL Diamond Certificate October 24, 2017 – Posted in: Jewelry Blog

There are a number of certification agencies operating in the US today. After the Gemological Institute of America (GIA) – arguably the most official of the companies providing the service – the Universal Gemological Laboratory (UGL) is generally considered among the companies that are next in line in terms of the quality and validity of the report they provide.

There’s no rule which says you even need to have a certificate to sell it on the open market, but having one will almost always mean a quicker sale for a higher price. This applies even more so if the certifying company is deemed reputable. Understanding any certificate is the key to knowing whether the diamond on offer is of a high quality or otherwise.

The UGL Certification

A UGL Jewelry Appraisal is intended as a guide to any piece of jewelry taken to them for appraisal and valuation.

The Appraisal itself is broken down into 4 areas. On the right hand side of the printed report will be at least one image of the actual piece at the time of valuation. In the above example, it is a diamond engagement ring. If the ring has features which are deemed important to the overall identification, usually images from more than one angle will be included.

On the left side, the report begins with a date of appraisal and the unique certificate number.


The bulk of the report is taken up by a broad description of the item, together with a more detailed appraisal of the diamond(s) used in the ring. If more than one diamond (or other stone) is present, these in turn will be appraised separately and distinguished by an alphabetic prefix – A), B) etc.

In our example, we know the item is a lady’s engagement ring with a round brilliant cut diamond. The diamond is 0.40ct, with the measurements of 4.80-4.75mm indicating its actual roundness. Ideally these would be the same, indicating a perfectly round diamond but, even with the latest techniques it is rare to see this measurement without a minor difference.

The clarity, we are told, is VS-1, which indicates the diamond is very slightly included when viewed at a 10x magnification. The gradings for clarity range from flawless to Included 3. Diamonds considered very slightly included, as is the case here, will include flaws and blemishes that can be fairly easily seen by a trained eye under 10x magnification, but will be difficult for the naked eye to see.

The color given is H, on a scale from D (colorless) to Z (light yellow), meaning this particular diamond is considered near-colorless.

Secondary Description

In the image, it is clear that this is not a solitaire ring, and more diamonds are present in the setting. These are appraised separately from the main stone, using the same grading scales for each element on carat weight (in this case the total weight of all the other diamonds), clarity and color, as well as the cut of the diamonds.

This section ends with a general appraisal of the polish and symmetry of the diamonds, based on the gradings awarded above.


Because the diamonds are set in a ring, it isn’t possible for the appraiser to offer an opinion on anything other than what can be seen in the finished piece, and so the phrase “Grading As Mounting Permits” is included. This, essentially, is a disclaimer to say that the diamonds haven’t been inspected to the same standard a loose stone would be.

This section also indicates the valuation is intended for insurance purposes. Insurance valuations are not used to value a piece for sale, as the resale and replacement values may actually be very different.


The UGL report does, however, include what it calls an “Estimated Retail Value” amount, but this is still only intended for insurance purposes.

The certificate is completed by including the official holograph seal of UGL, and the signature and printed name of the appraiser. In our example, Robert A. Lejman has the letters G.G (GIA) after his name, indication he is a Graduate Gemologist from the Gemological Institute of America, the world’s leading authority and source of education in gems and jewelry.

The UGL Diamond Certificate

The UGL Diamond Report is split into two sides. On the left is the actual grading for each of the Four Cs, together with specific size information and a few other details, and on the right is the scales used in the clarity and cut sections of the appraisal together with a picture of the actual diamond. The scales are those used throughout the industry, and so will be understood by anybody with experience of diamond grades.

The certificate will always contain the date that the report was compiled, followed by the physically measurable qualities of the diamond. In order, as seen in the certificate above, these are –

Shape and Cut

Almost all diamonds are cut to one of a number of recognise shapes, known by unique names. In this case, the cut is the Round Brilliant, which is the most popular diamond cut in use today. Because the Round Brilliant cut has specific requirements for the number of facets, together with measurement of the proportions of the cut stone (table, crown and pavilion), these aren’t specifically mentioned on the report and it is assumed that simply having the type of cut on there is sufficient for dealers and jewelry makers to know what it should look like.


This will always be comprised of 2 specific measurements. The first is always a smallest-largest measurement, in the case of a Round Brilliant cut, this is an indication of how round the polished stone actually is. The wider the gap between the two, the less round it actually is, with the ultimate aim being identical numbers either side of the divider.

The other measurement is the overall height of the diamond from the table to the culet. All dimensions are given in millimeters, as this allows a much more accurate measuring than if inches were used.

Carat Weight

The other measurable aspect of a diamond is the weight. Diamonds are always weighed in carats, an ancient measure based on fine grains of the Carob plant. One full carat is equal to 200 milligrams, or 0.2 grams, and is always stated as a decimal eg 1.5 carats is equal to 300mg. Technically, the carat is a measure of mass and not weight, but it is universally adopted as the unit of measurement for precious metals and stones.


The proportions of a cut diamond are very important, as these give a great deal of insight into the likely light-reflective and refractive properties of the stone. They can also affect the “carat look” of the stone.


The depth is a simple calculation of the depth (height) of a diamond by the width. The ideal depth is considered to be somewhere between 59.5% and 62.9%.


The table is the flat part of the diamond at the very top. In a Round Brilliant cut such as here, it is measured as a percentage of the overall width of the diamond. Ideal proportions are somewhere between 54% and 60%.


The girdle on a diamond is the thin line around the perimeter of the diamond where the crown of the top meets the pavilion of the bottom. Although the girdle is measured as a percentage of the overall size of the diamond, it is always stated in base terms from very thin to extremely thick. Too thin a girdle will leave the edges susceptible to damage, whereas too thick a girdle is considered displeasing from an aesthetic viewpoint. The ideal girdle is medium.


The culet is the very bottom of the diamond, which may have been cut to a small flat area or polished to a perfect point, and these can range from none to extremely large. No culet at all is considered ideal, but extra care must be taken when setting the stone, as the point is quite fragile. A Medium culet offers extra protection against damage, but may affect the stone visually.


The color  of a polished diamond is the most subjective part of any appraisal. Although most experienced appraisers will have very similar opinions of which color grade is appropriate, they do differ. The color is graded from D, which signifies colorless, to Z, which will have a quite marked yellow tint. Past this point, or for diamonds of other colors, they will be referred to as “fancy”. D grade is considered the optimal color.


The clarity of a diamond determines how many flaws or inclusions can be seen when using a 10x loupe to examine the stone. The scale goes from flawless to included, based on how many are visible when seen through a loupe. There is also an Internally Flawless grading which acknowledges that the diamond itself is flawless, but that there may be minor polishing or other marks on the surface. Flawless is the ideal clarity.


Finish is an assessment of the overall appearance of the diamond when considering the shape (symmetry) and the quality of the polish. These are based on the gradings as laid out above in the report.


When viewed under an ultraviolet (black) light, some diamonds emit a slight blue glow. This is caused by the presence of boron in the structure of the diamond, and can be either an advantage or disadvantage, depending on the grade of the diamond.

In colorless diamonds (grades D-F), any fluorescence will detract from the diamond, and may affect the value by up to 15%. This is despite it being accepted that almost nobody will see the difference in any natural light situation.

With diamonds containing some hint of yellow, fluorescence can help, as the blue helps to cancel out the yellow, making a visibly less colored diamond. This can occur even in natural light, and so fluorescence is seen as a definite advantage for many lower quality stones.

Other Information

UGL also offer the option of a dollar value grading on their certificates. Whether this is useful or not is questionable, as the value shown will only be appropriate at the time of the appraisal. The diamond market, in the same way as with any traded commodity, is subject to fluctuation, and the dollar value put on a diamond by UGL may give a misleading impression as to its true value at the time of sale.