Opal Treatments
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 enhancement, heating, painting, dying, resins and waxes, oiling or any application of chemicals. Opal is treated to change its natural appearance, structure or durability. Opal is colour enhanced in opal inlay jewellery where usually a thin solid crystal opal has black paint or glue applied or set above black painted jewellery.
COMPOSITE NATURAL OPAL
Composite natural opal consists of natural opal laminates, manually cemented or attached to another material. The opal component is natural opal. There are three main forms of composite opal:
Doublet Opals - are a composition of two pieces where a slice of natural opal is cemented to a dark base material.
Triplet Opals - are a composition of three pieces where a thin slice of natural opal is cemented to a dark base material and a transparent top layer, usually of quartz or glass.
Mosaic and Chip Opals - are a composition of small flat or irregularly shaped pieces of natural opal cemented as a mosaic tile on a dark base material or encompassed in a resin.
SYNTHETIC OPAL
Synthetic Opal is material which has essentially the same chemical composition and physical structure as natural opal but has been made by laboratory or industrial process. Synthetic composites exist as synthetic doublets, triplets or mosaics and must be disclosed as synthetic composites.
IMITATION OPAL
Imitation Opal is material which imitates the play-of-colour of natural opal, but does not have the same physical and chemical structure or gemmological constants as natural opal.
CLASSIFICATION REPORTS
Classification reports for the following types of opal should include these details:
Natural Opal
1. Type of opal
2. Variety of opal as Black opal, Dark opal or Light opal with a body classification from N1 (Black) to N9 (White) based on the AGIA Body Tone Chart.
3. Transparency as opaque, translucent or transparent. Note if it is crystal opal.
4. Weight and dimensions
Treated Opal
1. Type of opal
# Variety of opal as Black, Dark or Light opal
# Transparency as opaque, translucent or transparent. Note if it is crystal opal.
# Type of Treatment and process if known
# Weight and dimensions
Composite Opal
1. Type of composite as doublet, triplet, mosaic or chip opal
2. Treatment process, where relevant
3. Dimensions
Synthetic and Imitation
# Gemmological category including manufacturer (if known)
# Description (Body Tone)
# If composite, mention type as doublet, triplet, mosaic or chip
# Weight and dimensions, only dimensions if composite