Clarity refers to the inclusions and structural changes in the diamond crystal (tiny bubbles or a different 'grain' direction in the crystal, etc.). Gemologists use the same inclusions also as an identifying characteristic. One must remember that a diamond is a natural substance and any inclusion can be considered a diamond's unique natural characteristic and «fingerprint», that has been formed millions of years ago in the diamond formation process, and is not a sign of modern intervention and, for the most part, not a sign of faulty manufacturing etc. In a sense, inclusions make your diamond as unique as an individual snowflake, since no two are exactly alike.
Diamonds are graded for Clarity according to the number, size, location and type of inclusion. Obviously, less numerous and smaller inclusions that are less centrally located are more desirable.
The less included a diamond is, the rarer it is and, therefore, the more valuable it is.
The following terminology is used, by now universally, by the industry to indicate a diamond's Clarity level. All clarity definitions are based on examination under a ten time magnification loop.
FL and IF, or, Flawless and Internally Flawless, are grades referring to diamonds with no inclusions under 10X loop when examined by a trained professional. The Flawless grade does not allow a flaw anywhere in the diamond, while the more accessible and common Internally Flawless grade tolerates some surface imperfection (that, at a cost, may still be removed to create a flawless diamond).
VVS1, VVS2, VS1 and VS2 («Very Very Slightly Included» --more so: «2» or less so: «1», and «Very Slightly Included» --more so: «2», less so: «1»). Those grades refer to diamonds with «some noticeable inclusions under 10X loop» when examined by an expert, but, they will be difficult or very difficult to locate (VVS), or, easy or somewhat difficult to locate (VS).
SI1, SI2 («Slightly Included», more so: «2», less so: «1»). Those have «Some obvious inclusions under X10 loop», obvious for SI1, and Very Obvious for SI2. Some SI2 diamonds may have their inclusions visible to the naked eye with some effort.
SI3, I1, and I2 («Included», more so: «2» or SI3, or less: «1»). Those have «Inclusions noticeable or obvious by naked eye». SI3 is not used by all laboratories and is used in border-line cases when the inclusion not immediately noticed by the naked eye.
What are acceptable and what are the best clarity levels?
Clearly the diamonds with no inclusions will appeal to the perfectionist. However, in practical and theoretical terms the VS1 category is the cut-off point for what is considered to be a fine clarity grade as the inclusions of this grade are extremely small and difficult to see at 10X magnification. If arranged on a scale from left to right, from «Flawless» to «Included», to the left of the scale from the VS1 grade the differences between each clarity grade are significantly smaller than differences in clarity in the grades to the right of the VS1 category, where the tolerances for each grade are larger. SI grades are still considered to be very good to good, since their inclusions in most cases are not eye visible, especially when examined under normal lighting conditions. SI grades are considered good choices especially when combined with good color and cut, since their cost, due to their clarity is within popular price range and budget. VS1 grade may be regarded as the border between a very good clarity--(both VS grades) and the exquisite (the Flawless and VVS grades).
