The discussion focuses on the methods for creating synthetic opal, specifically the Stober method and the use of silica gel. The process involves adding ethyl silicate to a boiled weak alkaline solution to grow colloidal silica spheres, which requires careful monitoring of temperature, density, and pH. The growth of uniform spheres takes several months, culminating in a final product that can display color patterns. The entire process, including drying and heat treatment, can take up to a year to complete.
PREREQUISITESChemistry enthusiasts, materials scientists, and hobbyists interested in synthetic gemstone creation will benefit from this discussion.
First, you add a little ethyl silicate into boiled weak alkaline solution and colloidal silica will grow. After separating and eliminating the condensed coarse spheres, by a sedimentation method, you drip ethyl silicate through a cooling installation and you grow amorphous silica spheres using colloidal silica as seed. You need a few months to get growth of uniform spheres and also you have to check the growing spheres all the time by a spectrometer. For this purpose, checking and modifying the temperature, density, and pH of the solution is very important. You stop the dripping of the ethyl silicate when sphere diameter becomes around 550nm. Then you continue to boil them a few more days and the effects are concluded.
After you collect and remove alchohol by distillation, you transfer the suspending solution, which contains the grown-up spheres into the clear container, such as a beaker. Then you let them settle down quietly over a long period of time. It takes a few months for the spheres to settle into a regular pattern. Centrifugal force cannot be used to accelerate settling of spheres. A few months later you will see the play of color displayed by the settled spheres in the beaker.
After you aspirate and remove most of the upper solution, you must add some more fluid containing colloid silica and stir the spheres up then for a second time to allow settlement start. First, settled spheres in the beaker become the cores and the later settlings grow upward as columns. At this time, the superior column eliminates the inferior column. In mineralogy, we explain these as geometric selection (Grigorlev 1965) and honeycomb color patterns get larger and larger.
The settled spheres exist in gel conditions and moisture is only slowly removed by natural evaporation so that dryness takes a long time. The gel turns into solid condition by the heat treatment until the gel becomes silica-stacked spheres of amorphous silica. Under this process, you can make black opal and transparent crystal opals by adding several additives. It takes about one year for the whole process.