Focus on

Polished Diamonds


Introduced by the Gemological Institute of America (GIA), the 4Cs is the universally grading system, whose underlying premise is that the value of a polished diamond is decided by its respective scores for carat, clarity, color and cut.  But do they represent an adequate number of criteria to provide the definitive price of any given stone? Not so says gemologist Renée Newman, writing in Jewellery Business, a Canadian trade publication, in an article entitled “Diamond Evolution: Why the 4Cs is no longer an adequate pricing system – Jewellery Business.”

“Times have changed,” she states. “These days, cloudy and hazy diamonds are often used in jewelry, but their clarity grade on lab reports does not necessarily reflect their lower transparency and value. It’s also become much more common for diamonds to be treated to improve their color and apparent clarity grades—and the price difference between treated and untreated diamonds can be significant. Additionally, cutting style and shape are distinct price factors from cut quality and many gem labs now issue diamond reports with cut grades. High-quality lab-grown diamonds have become widely available and sell for much less than mined, natural diamonds. When all of these listed factors are considered, it becomes very clear the 4Cs is no longer an adequate pricing system.”

The diamond specialist and lecturer, Ms. Newman is the author of 13 gem and jewelry books including the “Diamond Handbook: How to Identify & Evaluate Diamonds,” which is now in its  third edition, and the “The Diamond Ring Buying Guide,” which in 2020 will be released in its eight edition.

According to Ms. Newman, in addition to the standard 4 Cs, there are four other criteria that can have a effects on the price of polished diamond. These include:



The price of diamond can vary significantly depending in its shape, which also is arguably the factor most susceptible to changing fashion trends. Certain cutting styles that once were popular, are more difficult to move today. There was a time, for example, when marquise shapes sold for more than rounds.

In general, however, round diamonds and priced higher than diamonds of the same caratage, color and clarity with a pear, marquise and emerald-shape cuts. Square-shaped diamonds are generally priced 15 percent to 30 percent lower than rounds, although brilliant-cut square diamonds, better known as princess cuts, are valued higher than step-cut squares.  

It not only about fashion, however. Optically, a perfect round cut has enough depth to optimize fire and brilliance, while certain fancy shapes are used because of the shape and lack of depth provided by the rough stone. 
Cutting style also impact on the price of fancy color diamonds, with the face-up color sometimes intensified by the shape.


Transparency refers to the degree that a diamond transmits light. According to Ms. Newman there are five categories of transparency: transparent, semi-transparent, translucent (where the diamond is cloudy), semi-translucent or semi-opaque (where only a small fraction of light passes through the stone) and opaque(where virtually no light can pass through the stone.

The higher the transparency, the more valuable the diamond.


Shape and transparency have always been factors, but treatments are a more recent development, as the technological means of enhancing a diamond’s appearance become more sophisticated. An untreated diamond will always be more valuable than a stone of similar weight that has been treated. 

The four most commonly encountered treatments are: fracture filling, which involves involves the injection of a clear substance into tiny cracks within a diamond to improve its clarity; laser drilling, which involves drilling a minute tunnel through the diamond with a laser beam in order to remove a dark spot buried inside the stone; High-Pressure, High Temperature (HPHT) treatment to improve color of a yellowish or brownish diamonds, or to produce brownish yellow, orangey-yellow, green, blue, and even pink color diamonds, and irradiation, which is used to create Fancy Colored Diamonds

While fracture filling can be removed or damaged if the diamond is subject to high temperatures, laser drilling, HPHT and irradiation are considered permanent treatments.


The newest factor that needs to be taken into consideration is how the diamond was created. Is it a product of nature, formed millions of years ago deep beneath the earth’s surface, or was it manufactured artificially in a factory or laboratory?

As laboratory-grown diamonds become more commonplace, the price differential has grown, and the trend is likely to continue as time progresses.


There are other elements that Ms. Newman did not take into consideration in her recent article. Among these are the diamond’s ethical status. In other words, is it possible for the company trading the stone to definitively demonstrate that the stone is not morally challenged, either through third-party certification by compliance institutes like the Responsible Jewelry Council (RJC), or through a  system by which it is possible to track the stone all the way to the mine.

Another factor is whether the stone is branded or not. Just as premium can be charged for certain bottled water brands, the same today is true of certain diamond brands, with De Beers’ Forevermark being the most prominent example.