Oil Paint: A paint made by mixing colour pigment with oil (generally linseed oil) to produce a slow-drying malleable sticky substance.

Op Art or Optical Art: An abstract art that uses precise, hard-edged patterns in strong colours and make the images appear to move.

Onyx: A traditionally black gemstone used to celebrate the 7th wedding anniversary.

Opal: This gemstone is believed to reflect the colors of all other gemstones.  Opal is the birthstone for October and the traditional gift for the 14th wedding anniversary.

Oval: A stone with an elongated round shape.  This cut is popular for color gemstones.

Omega Backs: Earrings with a clip back style in the form of the Latin letter omega.

Opal: A gemstone with silica deposits and water content which has a spectral display of flashing colors that move and shift as the jewelry piece is moved. Much opal mining occurs in Australia.

Open back setting - a setting in which the back of the stone can be seen.