- I1 and I2 - Included clarity grades (I1 and I2).
- IF - Internally flawless clarity grade (only very minor surface inclusions allowed).
- IGI - International Gemological Institute.
A privately-owned gemological lab with offices in Antwerp, Dubai, Hong Kong, Los Angeles, Mumbai, New York, Tel Aviv, Tokyo, and Toronto, among other cities.
- Imperfection - A generic term used by non-gemologists for inclusions or blemishes.
- Inclusion - an internal clarity characteristic in a diamond
These include crystals, needles, pinpoints, clouds, graining, twinning wisp, laser drill holes. The more inclusions your diamond has, the lower the clarity grade and the lower the value, especially if laser drill holes are present. Inclusions can also extend into the diamond from the surface. These include bearded girdles, bruises, cavities, chips, feathers, indented naturals and knots.
- Internal Graining - See Graining.
- Irradiated Diamond - a diamond exposed to radiation to alter its color to a fancy color
This is accomplished using neutron or electron bombardment. While irradiating a diamond might improve the color, it is an enhancement technique and consequently, has a negative impact on value. The GIA will specify on a grading report if the diamond has been irradiated.