DIAMOND GRADING FOR CLARITY
Internal features and inclusions may light transmission through a diamond, decreasing its brilliance and its clarity.
All characteristics found in or on a diamond can be divided into either:
a) Internal characteristics: Inclusions totally enclosed by the host diamond and those react with the surface of the gem.
b) External characteristics: Those that are found on the surface of the diamond but do not penetrate into the gem.
A) Internal characteristics
Crystal: A crystal of a diamond or any other mineral within the diamond.
Pinpoint: A minute small inclusion so small is observed only as a tiny dot.
Cloud: An aggregation of pinpoint and can vary in Colours.
Feather: A break in the structure of the stone. May or may not follow the grain of the diamond.
Bearding: Tiny feathers found on the circumference of the girdle extending into stone to a very small degree.
Structural phenomenon
Sometimes it is called ‘graining’. Usually, it takes the form of straight zoning. If it is whitish-colored or reflective then clarity is affected
External Characteristics
Natural
This term is used to describe part of the rough diamond crystal surface remaining on the polished diamond. If this natural penetrates the stone it is called an “indented natural” as an internal characteristic in the GIA system.
Extra facet
A small facet was added and unrelated to the usual facet pattern. One may be polished on the girdle to remove a surface defect, or when two adjacent facets do not meet during polishing, a third facet may be added.
Scratch
Surface damage on a facet may be caused by abrasion from other diamonds.
Polishing lines
Fine parallel lines on the facet, transparent or whitish in appearance, caused by poor polishing.
Surface growth line
External indication of internal grain. They may appear straight, unrelated to the polishing direction, or in an irregular manner.
Damage Mark
Minute pits are caused by a blow or percussion action during wear.
Chip
Sometimes it’s called Nick. A surface cavity lifts after a small part of the diamond has broken away, which is caused by the mishandling of gems.
Abraded facet edges
Caused by wear over a period of many years.
Twinning lines or nats
External line or parallel caused by polishing over the twinned area.
Requirements for grading:
Cleanliness of the stones
Use 10x magnification
Dark field illumination
