Opals of all varieties have been synthesized experimentally and commercially. The discovery of the ordered sphere structure of precious opal led to its synthesis by Pierre Gilson in 1974. The resulting material is distinguishable from natural opal by its regularity; under magnification, the patches of color are seen to be arranged in a "lizard skin" or "chicken wire" pattern. Furthermore, synthetic opals do not fluoresce under ultraviolet light. Synthetics are also generally lower in density and are often highly porous. Opals of all varieties have been synthesized experimentally and commercially. The discovery of the ordered sphere structure of precious opal led to its synthesis by Pierre Gilson in 1974. The resulting material is distinguishable from natural opal by its regularity; under magnification, the patches of color are seen to be arranged in a "lizard skin" or "chicken wire" pattern. Furthermore, synthetic opals do not fluoresce under ultraviolet light. Synthetics are also generally lower in density and are often highly porous.
Boulder opals are thin seams of opal that form in ironstone. These opals come in many colors and show dazzling fire, backed by their brown ironstone matrix. Crystal opals are colorless and transparent to semi-transparent in transmitted light but with a rich play of colors in reflected light. Black crystal opals are transparent to semi-transparent with dark body color and play of color.
Synthetic opals may show a strong display of color, usually in a mosaic pattern. Under high magnification with top or backlighting, a cellular, scale-like, snake skin, or chicken wire structure can be found in the pattern. Under high magnification with transmitted light, synthetics may show a dendritic structure. Synthetic opals were first created by Pierre Gilson in 1974. There are a number of compounds that can be used in the process, but the main idea is to use a polymer that allows the silica spheres within the stone to bind themselves to each other. Recently, a new form of synthetic opal has been manufactured known as Mexifire. Synthetic opals usually display a very distinctive snakeskin pattern and they show brighter colors than natural opals. The spots of color are larger but they interact with light in a very similar way to natural opals. They also contain a fair amount of silica (usually around 70-75%) which is impregnated with plastic. Synthetic Opals look good and appeal to some but cant replace what Mother Nature creates. Synthetic opals differ from naturally occurring opal stones in that the former are made entirely in the laboratory. Some individuals may choose to purchase synthetic opals for two main reasons. The first reason is that these stones are significantly stronger and more durable than naturally occurring opals. This is primarily because unlike natural opal stones, synthetic opals do not contain even trace amounts of water within them. The second reason is that of price. Since synthetic opals do not actually contain any of the precious opal compounds, they are priced substantially lower than their natural counterparts. Synthetic opals don't phosphoresce. They may also stick to the tongue. Synthetic white opal can show columnar structures from the side. Some synthetic and imitation opals have been sold under trade names that have been at least temporarily popular. A material sold as "Gilson Opal" or "Gilsonite" is a lab-created material with a chemical composition that departs from the hydrous silicon dioxide chemistry of natural opals. "Slocum Stone" or "Slocum Opal" is another variety of opal simulant. During the 1960s and 1970s these and other opal silmulants were popular. These materials can be beautiful with wonderful color. A hint that you are looking at one of these early opal simulants is when you see play-of-color that is in a patchy to blocky pattern. The stone at right is a Gilson Opal about 20 mm in height. One of the key ways in which synthetic opals differ from natural opal stones is in their pattern. While it is possible to find natural opals with regular patterns, these are quite rare. Conversely, synthetic opals created in laboratories will almost always have an unusually regular pattern. The regular pattern witnessed in synthetic opals also create a brilliant 'play of colour' that will not be seen in naturally occurring opal stones. There is a difference between “synthetic” opal and “imitation” or “faux” opal. Synthetic opals are made in a laboratory from the same chemical (silicon dioxide) that occurs in natural opals. The process was developed in the 1930s and thus synthetic opals have been around for about eighty years! Some of them look very much like natural precious opal but there are several ways to tell them apart: (1) The colors in synthetic opal are usually brighter and occur in larger patches, often with a sort of ‘snakeskin’ pattern (2) Under magnification the color patterns will appear more regularly geometric than those in a natural opal and (3) The overall pattern appears more ‘neat and orderly’ than those in the naturally formed stones. This sterling silver bracelet is inlaid with lab created opal.
Contra Luz: Literally, “against light”; this is a pattern effect seen only in some crystal opals and means that the colorplay is visible when the stone has the light source behind it rather than in front. Normally the colorplay in a stone will disappear in this orientation but if it does not, then the crystal opal has a contra luz pattern.