Illusion: An Illusion setting is when the surrounding of a gemstone is made so that it reflects the gemstone and makes it look bigger.
Imitation: When one material is made specifically to look like another. For example, a paste stone or a clear diamante might imitate a diamond.
Imperial Jade: Emerald green coloured translucent jade – highly prized.
Inclusion: this refers to flaws and minute foreign bodies inside a gemstone. In some stones, they are expected for example in Emeralds. In diamonds, the amount and size of inclusions make a huge difference to the value.
Inlay: Thin pieces of a material set into the jewellery and with a flat surface created. For example Pique tortoiseshell
Inscribing / Inscription: Words, letters or a design carved into jewellery
Intaglio: The opposite of a cameo. The design is carved into the reverse of a gemstone. It is viewed from the top.
Iolite: a denim blue gemstone often has darker grey inclusions, usually seen as a cabochon
Iridescence: a pretty rainbow effect seen on some gemstones
Ivory: From animal tusks usually elephants. Popular in jewellery in the Victorian era. Not found on AntiquesAvenue as I believe that the trade in Ivory even antique pieces encourages the market in new pieces.