The art of revealing what is inside
A rough opal rarely delivers immediately what it holds. It is in the cutting that the stone reveals its personality: the lapidary must read the internal structure, identify how light behaves within the gem, and make decisions that will determine the character of the final piece. Few processes in jewelry demand as much judgment as opal cutting.
Types of opal cuts
Unlike diamonds and other hard gems, which are often faceted to maximize light reflection, precious opals are almost always worked into a cabochon format, a convex polished surface without facets. This is because the play of colors in opals depends not on reflection but on diffraction, and the curve of the cabochon amplifies this effect.
The main cutting forms used for opals are:
- Simple cabochon: the most common form, flat base and convex top in varying heights
- Double cabochon: convex on both sides, used when the stone has sufficient thickness and uniform play of colors
- Solid opal: cut from a single stone with no reinforcement, the most commercially valued form
- Doublet: a thin layer of opal bonded onto a dark base (usually obsidian or onyx) to imitate the visual effect of black opal
- Triplet: a layer of opal between a dark base and a transparent crystal or quartz cover for protection and brightness amplification
It is essential that buyers know how to distinguish between a solid opal and a doublet or triplet, as commercial value differs substantially. An ethical lapidary always discloses the nature of the piece.
How the lapidary reads a rough opal
Before any cut, the lapidary carefully analyzes the rough stone, considering:
- Play-of-color orientation: silica spheres are arranged in specific planes; correct orientation of the cabochon relative to these planes maximizes color visibility
- Inclusions and fractures: internal flaws that may compromise integrity or, in some cases, create interesting visual effects
- Color distribution: whether uniform, concentrated in specific areas, or layered
- Optical layer thickness: the layer generating the play of colors must be preserved as much as possible
Weight and proportion: less is more?
In opal cutting, unlike diamonds, final weight is not always the priority. A lower cabochon may display cleaner, more uniform colors than a taller one. The decision on ideal height is simultaneously technical and aesthetic.
The finest lapidaries of Piaui have developed over decades a hereditary knowledge of local stones, able to anticipate what each batch holds before the process even begins. This artisanal knowledge is invaluable and forms part of the cultural heritage of Pedro II.
The relationship between cutting and design
For a contemporary jeweler, the conversation with the lapidary begins before the stone is finished. The final cabochon form, its height, proportion, and outline directly affect the possibilities for setting and the character of the piece. An opal is not a passive component: it sets the tone for the entire jewel.
Working with opals demands an openness to surprise and collaboration with the material itself. Rarely does the design come first; often, it is the stone that suggests what it wants to become.
Source: GOMES, C.B. et al. As Opalas do Piaui [The Opals of Piaui]. Brasilia: CETEM/MCTI, 2025. Part of Fortes Jewellery's educational gemology series, based on scientific research by the Centro de Tecnologia Mineral of Brazil's Ministry of Science, Technology and Innovation.