Diamonds are formed in the earth's crust under extreme conditions of pressure and temperature.  Rough diamond crystals can take millions of years to form.  Rough diamonds reach the earth's surface by volcanic eruptions and can be found in volcanic pipes or alluvial depositions (rivers and seas) from where they are mined. 
A large proportion of the diamonds found are of industrial quality.  They cannot be used as gemstones because they are full of impurities and cracks.  Because of the hardness of diamond they are still useful for industrial cutting and drilling tools. 
A smaller fraction of the rough diamonds found are of gem stone quality.  These stones are cut and polished to be used for precious jewelry or other luxury goods.  There is a market for polished diamonds, because of their value and brilliant appearance. 
It is clear that the rarity of gem stone quality rough diamonds make them precious.  It is the task of a good cutter to cut and polish a rough stone in such a way that the loss of material is minimal and the polished result has the highest possible value. 
The value of a polished diamond Is determined by four factors, called the 4 C's namely carat, clarity, colour and cut Each of these factors are judged in a certificate. 
Cut A good cut gives a diamond its brilliance, that is the brightness which seems to come from the very heart of a diamond.  The angles and finish of any diamond are what determine its ability to handle light, which leads to brilliance.  The quality of the “cut” does make a difference in how a diamond looks. 
Clarity: Most diamonds contain some inner flaws, or inclusions, that occur during the formation process.  The visibility, number and size of these inclusions determine what is called the clarity of a diamond.  Diamonds that are clear create more brilliance, and thus are more highly priced.  When we speak of a diamond's clarity, we are referring to the presence of identifying characteristics on and within the stone.  While most of these characteristics are inherent qualities of the rough diamond and have been present since the earliest stages of the crystal's growth below ground, a few are actually a result of the harsh stress that a diamond undergoes during the cutting process itself. 
When the incredible amount of pressure is considered that it takes to create a diamond, it is no surprise that many diamonds have inclusions—scratches, blemishes, air bubbles or non-diamond mineral material—on their surface or inside.  Thus, diamonds with no or few inclusions and blemishes are more highly valued than those with less clarity, not just because they are more pleasing to the eye, but also because they are rarer. 
Color: Colorless diamonds are the most desirable since they allow the most refraction of light (sparkle).  Off-white diamonds absorb light, inhibiting brilliance.  When jewelers speak of a diamond's color, they are usually referring to the presence or absence of color in white diamonds.  Color is a result of the composition of the diamond, and it never changes over time. 
Because a colorless diamond, like a clear window, allows more light to pass through it than a colored diamond, colorless diamonds emit more sparkle and fire.  The formation process of a diamond ensures that only a few, rare diamonds are truly colorless.  Thus the whiter the color of a diamond, the greater its value. 
Carat: A carat is the unit of weight by which a diamond is measured.  Because large diamonds are found less commonly than small diamonds, the price of a diamond rises exponentially according to its size.  A carat is a unit of measurement.  It is the unit used to weigh a diamond.  One carat is equal to 200 milligrams, or 0.2 grams.  The process that forms a diamond happens only in very rare circumstances, and typically the natural materials required are found only in small amounts.  That means that larger diamonds are found less often than smaller ones.  Thus, large diamonds are rare and have a greater value per carat.  For that reason, the price of a diamond rises exponentially to its size. 
The challenge for the cutter is to optimise a diamond towards the four C's.  This optimisation process is mainly done by craftsmanship and relies on manual skill and experience of the craftsman.  However, this has the disadvantage that the craftsman has to visualize the several possibilities for cutting the diamond, and decide upon the most optimised cutting regime.  Furthermore, while the relationships between value and the 4 C's are known, they are non-linear and are interdependent.  Where maximizing the value of the rough diamond is important, the craftsman might not recognize the possibility of other, more valuable cutting regimes due to the multiple factors involved.  In most cases more than one stone is polished from the same rough, what makes the optimal cutting even harder. 
Furthermore, the diamonds resulting from an optimised cutting regime might not be of interest to the client.  A client might be prepared to make an additional cost for a diamond of a particular clarity, cut, colour and carat.  If the craftsman was able to provide a client with a way to see the rough diamond, and the possibilities for cutting, before the diamond was actually cut, the client would be better served, and the value of the rough diamond would be enhanced. 
Furthermore, a client gains satisfaction and pride in owning a diamond.  The authentication certificate that presently accompanies a diamond indicates certain measurable parameters of the diamond, and is almost as important as the diamond itself in reassuring the owner of its value.  Another parameter which is not indicated on the certificate, but which can be of equal value to the client, is the history of the diamond.  A client would be further reassured to know from which rough stone the diamond came and how the diamond was optimised for cutting and polishing.  Furthermore, the value of a diamond accompanied by this information would be enhanced over the same diamond lacking such information.