The more pure or vivid colour saturation of the Opal will also increase the value. Patterns in Opal are also a factor to consider. Size, shape and regularity of the colour patterns is also important. The direction of the colour and pattern is also highly notable. When rolling the gem from side to side, see if the colours are visible in all directions.
Inclusions in the Opal such as Potch patches or Potch Lines will effect the value, so determine what they are, how many and their position within the face of the stone. Carat weight of the gemstone like other gemstones plays a part in its value.
The Australian Opal and Diamond Collection does not stock or sell any treated, colour enhanced or synthetic opal.
The Diffraction of Opal
Depending on the size of the spheres, varying colours of the light spectrum are diffracted. So it is a combination of deflection (bending) and diffraction (breaking up) of light rays that creates the colour in opal.
If you move the stone, light hits the spheres from different angles and brings about a change in colour. The name opal actually means "to see a change in colour." The way in which colours change within a particular stone as it is rotated and tilted is called the stone's play of colour.The colour Red is most valued, followed by Green, and lastly Blue.