Impasto: A style of painting characterized by thick, juicy colour application.

Imprimatura: A thin, veil of paint, or paint-tinted size, applied to a ground to lessen the ground's absorbency or to tint the ground to a middle value.

Impressionism: An art movement originating in France in the 1860s, the main artists concerned being Cezanne, Degas, Monet, Morisot, Camille Pissaro, Renoir and Sisley.  They were concerned with representing day-to-day existence in a realistic way, recording the fleeting effects of light and movement.  Their usual subjects were landscapes or social scenes.

Indian ink: A black ink originally from China and Japan, consisting of finely divided carbon suspended in a solution of gum, glue or varnish.

Icon or Ikon: A religious image often that of a saint, painted on a wooden panel.  The word comes from Greek word eikon meaning likeness.

Intaglio: The cutting into a stone or other material or the etching or engraving on a metal plate of an image. The opposite of relief.  Intaglio printing techniques include engraving and etching.

Intensity: The purity and brightness of a colour. Also called saturation.

IGI: International Gemological Institute.  The largest independent institution that certifies gems and appraises diamonds.

Inclusions: The natural birthmarks inside a stone that can affect its flow of light and also add uniqueness and character.  Inclusions vary in size, shape, quantity, position and color.

Inlaid Setting: A portion of the metal setting has been cut away and replaced by a stone.  In this setting, the stones are flush with the metal surface.

International Gemological Institute (IGI): An international organization that independently certifies diamonds as to their quality and authenticity.

Invisible Setting: Several stones are mounted together by metal under the stones.  The metal cannot be seen from above, making the stones appear as if they have no setting at all.