Reference:

ABOUT OPALS

What is a Andamooka Matrix Opal ?

Andamooka matrix opal is a porous material from Andamooka, South Australia, which is often treated to enhance the colour by depositing black carbon by chemical treatment in the pores of the stone.

	Fig. 12. Treated (carbonised) dark Andamooka matrix opals. (Photograph, R. Weber)

OPAL TREATMENTS
Opal can be subjected to various types of treatment. Present CIBJO guidelines state that any method of treatment other than standard cutting and polishing must be disclosed and the process used specified on all invoices, advertising, and commercial documents. Types of treatments include colour and/or tone enhancement (Fig. 12), heating, painting, dying, resins and waxes, oiling or any application of chemicals. Opal also may be treated to change its natural appearance or durability. The body tone of opal is often enhanced (usually appearing darker) in some opal inlay jewellery where a thin piece of solid crystal opal has black paint or black glue applied, or the opal is set above black painted jewellery.

Andamooka Matrix Opal

Black or darkish bodied opal with bright specs of colour. This is chemically treated Limestone matrix with precious opal in voids. Not common.

Andamooka South Australia opal field

Find more information at the OPAL Association's Opal Nomenclature Section of their Website:

http://www.opal.asn.au/information_nom