Hydrated silica, often known as silicon dioxide, makes up opal. Water content varies in it. Opals in nature occur in two types. Common opals are usually one hue and come in transparent, white, red, and black varieties. The other form is known as precious opal and is gem-quality opal. The rainbow that shimmers as the precious opal is spun in the light is one of its most distinctive features. Opals are being created in laboratories in an effort to replicate the exquisite beauty of naturally occurring precious opals. In the lab, opals are produced in three different categories: imitation, synthetic, and artificially generated.
The basic process of opal synthesis consists of three stages. First, scientists create tiny silica spheres. Next, they arrange the spheres in a lattice pattern to imitate the structure of precious opal. Finally, they fill the pores of the structure with silica gel and harden it. The process can take more than a year. The result is a hydrated silica product that exhibits iridescence and has a similar appearance to that of natural opal. The most difficult part of opal synthesis is recreating the rainbow fire of natural precious opal. Pierre Gilson created the first synthetic opal in 1974, and the early attempts had bands of iridescence rather than sparkles. Researchers adjusted the process and created lizard-skin iridescence.
The opal photographer and historian Len Cram started experimenting with novel opal-growing techniques in the 1980s. Cram had his doubts about the conventional theory of how opal creation came to be after hearing tales of opalized skeletons and fence posts around opal mines. Others proposed that over hundreds of years, silica filled up spaces in the ground and crystallized into opal. Opals, in Cram's opinion, grew more fast. He believed that chemical reactions involving substances found in the soil produced opals. Using this hypothesis as his foundation, Cram developed his own opal-making procedure. He develops opals that are optically indistinguishable from natural opals in a matter of months by combining opal dirt with liquid electrolytes.
At least three different forms of synthetic opals are available right now: Slocum stones, opal essence, and opals produced via the Gilson method. It is challenging to distinguish naturally occurring opals from Slocum stones or opal essence stones with the naked eye. However, compared to Gilson opals, Slocum stones and opal essence are mostly used for ornamental and jewelry purposes.
There aren't many differences between Gilson opals and natural opals. In fact, according to Chemical Engineering News, water is the only element absent from Gilson opals. Gilson opals cannot be distinguished from naturally occurring opals without a jeweler's rigorous inspection. This distinction is known as the "lizard-skin" effect, where the lack of water generates minute ripples on the opal's surface.