How to estimate the value of a gem stone ?
The GIA (Gemological Institute of America) came up with a set of criteria in the early 1940s to help experts define the value of a diamond in the most accurate way : the
4C’s and the International Diamond Grading System.
These methods are the world’s standard and the universal benchmarks by which all diamonds are judged.
The 4 C’s stands for : Carat, Color, Clarity, and Cut.
In 1953, the GIA introduced the D-to-Z color scale, choosing the letter “D” for the top grade (colorless) precisely because the letter had negative associations and so was unlikely to be misinterpreted or misused.
The GIA Clarity Scale today consists of six categories ranging from Flawless to Included and contains 11 specific grades.
The Cut Scale, ranging from Excellent to Poor, describes how successfully a diamond interacts with light to deliver the brightness, fire and scintillation we associate with a fine round brilliant.
To put it simply, diamond carat weight measures how much a diamond weighs.
A metric “carat” is defined as 200 milligrams. Each carat is subdivided into 100 ‘points to allow very precise measurements to the hundredth decimal place. A jeweler may describe the weight of a diamond below one carat by its ‘points’ alone. For instance, the jeweler may refer to a diamond that weighs 0.25 carats as a ‘twenty-five pointer.’
Diamond weights greater than one carat are expressed in carats and decimals. A 1.08 carat stone would be described as ‘one point oh eight carats.’
Diamond price increases with diamond carat weight because larger diamonds are rarer and thus, more desirable. However, two diamonds of equal carat weight can have very different values (and prices) depending on three other factors of the diamond 4Cs.