There are four main parameters for evaluating the value of a diamonds.
These parameters are called "The four C`s
Carat - weight
Clarity - Level of cleanliness
.Needs to be noted that it is impossible to find two identical diamonds in nature and as similar as they can possibly be, a skilled professional with the right tools will be able to tell the difference.
In general, a non skilled individual without any experience in the diamond industry will be able to find differences in two out of the four parameters:
The weight of a diamond, which can affect its Diameter.
The color of a diamond, done by comparing two diamonds.
The other two parameters, Clarity and Cut are more complex to define and require guidance and use of auxiliary equipment.
Clearly, there are other parameters that affect a diamonds value and beauty, such as symmetry of the diamonds surfaces, the polishing level, the culet, the Rondyst thickness, level of fluorescence, but these four are the most important and, in many cases, the only ones taken into account when evaluating Diamond.
Today, the diamond is recognized worldwide as a symbol of eternal love and many people present it to their loved ones not only because of it`s great value but also for its mysticism and what it symbolizes.
All these, and of course, it`s beauty and brilliance, are what makes the diamond what it is today.
The differences and subtleties of a diamond are documented in gemological certificate. When buying a diamond, even if it is embedded within a Jewel, it's preferable to demand such a certification to be sure, that the selling diamond is the one accepted
It is importent to know that the correct way to assess a classification of the diamond and in fact reveal its quality is prior to setting it into a jewel, when it is exposed from all sides and angles.
Evaluating a diamond after it is set is incorrect and nonprofessional!