Sorting and Valuing Rough Diamonds

Sorting and Valuing Rough Diamonds:

The Rough Diamond Course covers the following FAQ.

What does diamond sorting actually involve ?

The diamond subject dealt with in the course are rough diamonds, and the sorting taught to is the sorting of rough diamonds into their respective categories for valuation, prior to their polishing and manufacture.

Polished diamonds are also sorted into grades after polishing, but there is a fundamental difference between sorting rough and grading polished.

When grading polished the approach is to grade what physically exists and that can be seen under ten times, or greater, magnification, with regard to cut and quality.

Although the sorting of rough involves the similar search for physical imperfections, there are also options available for possible improvement, in terms of quality and color, during manufacturing.

While improvement of a polished diamond is theoretically possible, it comes at the cost of having to re-polish the stone, resulting in a smaller yield and additional manufacturing cost.


Why do we want to learn how to sort diamonds?

Why it is necessary to sort rough diamonds at all ?

The fact is that no two diamonds are exactly the same. The origin, and crystallisation of carbon to form diamond will be  covered in depth on the course, diamonds crystallize in the Cubic system, either as eight-sided octahedrons or as simple cubes, no two diamonds are identical.

As long as diamonds remain within their stable environment, below the earth’s surface, the crystallisation process occurs unhampered. However, it is during the passage of diamonds from deep underground up to the earth’s surface that considerable damage can occur. This process, known as re sorption, sees diamonds subjected to extreme changes of temperature and pressure, which can not only bring about physical breakage of the diamonds, but damage to the crystal lattice too.

This means that each and every diamond is unique in tenus of its overall combination of shape, color, quality and size. Diamond manufacturing is so specialized, these four characteristics have led to the Diamond Cutting and Polishing industry creating a whole range of different categories.

Over time these categories have expanded until today there are something in the region of sixteen thousand categories of diamonds produced from around the world.

Sixteen thousand may sound a considerable figure for sorters to contend with, but in practice the reality is a little different. Also, it needs to be mentioned that no single diamond producing country produces all of these sixteen thousand categories.

What is sorting diamonds about?

Sorting is about looking at a rough diamond and assessing four important features pertaining to its appearance.

This is where the GIA (Gemological Institute of America) famous four Cs of the diamond enter the training, and in order to understand the sorting of rough diamonds better, it will be necessary to examine each of the four Cs in turn.

With some 16,000 categories to master, considerable skill is required from diamond sorters, in order to ensure that each and every stone is placed in its appropriate category. The reason that so many categories exist is due to size variations, where generally speaking the larger a diamond is, category by category, the greater is the value.

The metric carat is universally adopted as the scientific unit of measurement applied to diamonds.
The metric carat is 0.2 of a gram, thus 5 carats weight 1 gram.

The word carat should not be confused with its namesake, when applied to gold. With diamonds, carat refers to weight, but when applied to gold it refers  to purity, thus 24-carat gold is pure gold.

When sorting rough, it is not only the presence of these imperfections that determines the value of the stone, but also where these imperfections exist within the stone. If these imperfections are situated on the peripherals,
polishing could possibly remove them thus leaving the polished stone unblemished. However, should polishing not succeed in removing them in their entirety, at least they will be confined to the girdle, where their presence
can be minimized, by being covered by a claw when mounted in jewelry.

What is the Ratio between Gem and Industrial diamonds?

Some twenty five years ago the average diamond mine around the world was 20% gem and 80% industrial. There was a noticeable corresponding cost differentiation between these two categories, which meant that the value of the gem had, to a large extent, to cover the cost of mining the industrial.

With advances in the latest diamond equipment and technology, and the introduction of lasers, the last twenty years has seen the dramatic growth of a middle category called near-gem.

Near-gem is so called because it is almost gem quality, and value, but not quite. In fact it has been developed from the top thirty percent of the industrial assortment.

These diamonds contain small clean areas, along with very poor areas.

The rationale behind this part of the assortment is that the stones can be broken open, the clean areas polished into small gem quality stones, and what remains sold on for industrial purposes. The growth in popularity of these goods has seen an increase in the prices of the top end of the industrial range, 3.1.3 CUT which has led to the establishment of the new category, near-gem.

Diamond mines that were marginal mines have been able to be  kept open as a result of the increased value
attached to the 30% near-gem.

In the course we cover the diamond cut which refers to the physical shape of the rough diamond, for this plays an
important part in determining the potential yield of the stone. There are two basic shape categories into which diamonds are usually sorted. These are:,,,,

Sawable, for those stones that can be sawn to produce two or more smaller diamonds, and Makeable, which denotes that the stone will be “made” as it is,  or cleaved.

The role of the manufacturer is to obtain the largest possible clean diamond, and thus the decision to saw or “make” a diamond is of vital importance, and can usually determine the economic viability of the stone. The general “rule of thumb” is that octahedrons and do-decahedrons (twelve-sided), and rounder, bulky stones tend to be sawn, while the more broken, twisted, flatter stones tend to be made and polished as they are.

However, this does not take into account the existence of several categories of “difficult” stones, which present the
manufacturer with additional challenges. Several categories of ‘problem” or “difficult” stones exist within the assortment, and they need to be identified within the assortment: Twins, are, as the name implies, are where two or more stones have fused together, or an inter-penetrant twin, where it is difficult to differentiate where the various sawing and cleaving grains occur.

Every diamond has an internal grain structure, which permits how and where a diamond can be sawn or
cleaved, rather like wood. However, diamonds can only be sawn along a sawing grain and cleaved along a cleaving grain. Any attempt to do otherwise usually ends in a disaster. Macles, are inter-penetrant twins where one part of the stone has the sawing and cleaving grains in one orientation, which then differs from the corresponding grains in the other part of the stone.

Cubes, are stones where although the sawing and cleaving grains exist, they are not that easily identifiable. Furthermore, such stones, if sawn or cleaved, tend to produce awkward models for polishing, with accompanying loss of yield.

The advent of laser technology has meant that former problem stones, such as a macle or a twin, can now be cut by means of a laser, without regard as to where the respective sawing or cleaving grains lie.

There are only a handful of basic colors, they can be expanded out to over two hundred different shades, which cover the range of the visible spectrum from colorless to light green, green, yellow, dark yellow, light and
dark brown, and even grey and black.

How long does it take to become a diamond sorter?

The Corlia Roberts Rough Diamond Grading Course is a two week course and will give you a good foundation, no two stones are the same, and in order to be able to  truly master the full range of the assortment, of  all 16,000 categories, a diamond sorter will constantly be learning and gaining the skills over time.

Enroll today and study the art of Diamond Sorting>>More or you can contact the Corlia Roberts Diamond Education College on +27739990999 / Whatsapp/ +27813190211