Opal Science

Opal Science Beginnings

Right up until the twentieth century when the electron microscope was invented, scientists of the time knew almost as little about opal gems as the first indigenous caveman that walked the earth tens of thousands of years ago.

Now that we have modern tools like the electron microscope, the once mysterious opal has not only given us its’ secrets but led us into the even more intriguing realms of nanoparticles and photonic crystals. Imagine a sphere made of amorphous silica (a cousin of sand) that’s only a billionth of a meter (nanometer) in diameter being bounced around like a basketball by all the water molecules surrounding it and then a million quadrillion more swimming around in between the layers of the earth, gradually falling to the bottom of a vug in the middle of a vein of rock and stacking themselves up in rows like oranges in the supermarket. That structure can become a photonic crystal and form a gem quality opal.

This stacking, or self assembly is only possible if the spheres are very close to the same size. Imagine stacking watermelons and potatoes and tomatoes and bananas and cherries and grapefruit together. They would all fall into a different pattern and if made of amorphous silica would become what we call common opal, which would be just an ordinary rock and not at all the gem like opal structure you will see being made in your test tube.

We don’t exactly know how nature forms these equal sized spheres although some people speculate and theorize. Your spheres were synthesized using water, alcohol, ammonia and tetraethylorthosilicate using a similar method to that invented by W. Stöber synthesized silica spheres by hydrolyzing TEOS in mixed solutions of ammonia, alcohol and water in 1968, with others in the1960’s but with some clever differences – our secret sauce if you like. The spheres in your opal science kit are close to the same size and range from about 200 nanometers to 400 nanometers in diameter. Put them in a still place and allow them to settle undisturbed for about 3 weeks. After about a week, you will see the spheres settling and they will begin to form what is known as a diffraction grating – they begin to exhibit what is called Bragg diffraction, a phenomenon whereby an incident white light is split into its component colors and reflected back to you in the form of several different and beautiful colors.

Try shining a flashlight up to them and as you move the light around, you will see the colors change before your eyes. Make sure you use a real flashlight and not one that has an L.E.D. or it won’t work as well. A number of sizes of spheres are available which will exhibit predominantly blue, green or red or colors in between depending on the size of the spheres in your test tube.