By Michael Adkins – Updated Mar 24, 2022

Natural and Synthetic Opals

Opals are celebrated semi‑precious gemstones, with more than 95% of natural specimens sourced from Australia’s desert regions. While nature produces a diverse array—from colorless common opals to the vibrant, fire‑red fire opals—artisans and scientists can also create synthetic versions that rival their natural counterparts in appearance and durability.

Categories of Synthetic Opals

Three primary synthetic techniques are in use today:

• Slocum Stones – Produced by evaporating a silica solution; they are almost indistinguishable from natural opals under casual inspection.
• Opal Essence – A liquid‑based process that yields opals with subtle play‑of‑color; primarily used for decorative purposes.
• Gilson Process – Developed by French chemist Pierre Gilson in 1974, this method mimics the natural crystal growth of opals and is the most versatile for both jewelry and scientific applications.

The Gilson Process Explained

Gilson opals are grown from a silicon seed that begins to crystallize in a controlled environment. Once the seed is established, the opal develops over 14 to 18 months, forming a precisely ordered silica structure. According to Chemical & Engineering News, Gilson opals differ from natural stones only in the absence of water, which manifests as a subtle “lizard‑skin” ripple pattern on their surface.

Comparing Natural and Gilson Opals

Because Gilson opals lack the moisture found in natural specimens, they are exceptionally resilient. This attribute makes them ideal for high‑performance applications, while their optical properties remain virtually identical to those of mined opals. Jewelers can distinguish Gilson opals only through meticulous, professional examination.

Applications of Synthetic Opals

Beyond adornment, Gilson opals are increasingly employed in scientific research. Their structural perfection allows them to serve as substrates for photon‑based data transfer and other advanced technologies. In contrast, Slocum stones and opal essence are mainly used for decorative jewelry due to their limited durability.