The Fire Within: Demystifying Opal's Play of Colour
Few natural gemstones can rival the mesmerising qualities of opal. With a flash of light, it reveals a shimmering kaleidoscope of colours that appear to move and dance across the stone's surface. This incredible optical effect is known as "play of colour," and sometimes, "fire." But what is the science behind this magic? The answer lies in the very structure of the opal itself.
The Building Blocks of Brilliance
To understand why opal has this captivating quality, we must look at how it's made. Under a powerful microscope, the surface of an opal reveals a fascinating sight: a perfectly ordered arrangement of tiny, spherical beads. These are spheres of silica, the primary material that makes up opal. The magic of the play of colour happens as light interacts with this precise, microscopic structure.
The Science of Play of Colour
Imagine a single ray of light entering an opal. As it travels, it encounters these perfectly aligned spheres of silica. There are minuscule gaps between the spheres. Light, as we know, is a spectrum of colours, from blue to red. The size of the gap between the silica spheres is so precise that it can act as a filter.
When a ray of light hits the side of a silica sphere, some of it will be diffracted or bent. The gap between the spheres will only allow certain colours of the spectrum to pass through. For example, the gap might be so small that it "knocks off" the red light, allowing only the blue to pass through and be seen by the eye. In another part of the stone, where the spheres and gaps are a different size or angle, the red light might pass through, creating a stunning flash of crimson. This is why you see so many colours seemingly moving across the surface—the light is passing through different microscopic formations within the stone.
What This Means for Opal Quality
This scientific principle also directly impacts opal quality. The rarest and most sought-after colour to see in an opal is red. The oranges, blues, and greens are more common, which makes an opal with a prominent red "fire" significantly more valuable. This is also why collectors get so excited about an opal that displays a full spectrum of colour. A piece of opal jewellery that shows the full range from blue to red is a true marvel of nature.
The next time you gaze upon a piece of opal jewellery, you can appreciate not only its ethereal beauty but also the incredible natural science at play. It's a reminder that some of the most beautiful phenomena in the world are hidden just beneath the surface
