When it comes to precious gemstones, there is one optical phenomenon that captures gem lovers, and that is dispersion. This "fire" as we call it in gemology is the vivid play of rainbow colours that flash across a gemstone when it interacts with light.
What is dispersion?
Dispersion occurs when light enters a gemstone and separates into its individual spectral colours. White light, although it appears neutral to the naked eye, is actually a combination of colours with varying wavelengths. As this light refracts within a gemstone, its components fan out to create a spectrum of red, orange, yellow, green, blue, and violet hues. This is why a diamond’s brilliance can reveal fiery flashes.
In physics, dispersion is a measurable quality. Gemologists quantify it by comparing how different wavelengths of light—longer red and shorter violet—bend within a gemstone. Instruments like refractometers help determine the refractive index of a stone, making dispersion not only an aesthetic, but also a tool for gemstone identification.
The role of cutting and setting
The amount of fire a gemstone exhibits isn’t just about its natural properties—it’s also influenced by the lapidary artists skills. A skilled cutter shapes the facets of a gemstone to maximise its brilliance, precisely angling them to direct and refract light for optimal dispersion. The setting also plays a part, as metal choices and design can either amplify or dull a gemstone’s fire.
For instance, brilliant-cut diamonds are renowned for their fire due to their symmetrical arrangement of facets, designed to enhance light performance. Similarly, a coloured gemstone like zircon—known for its high dispersion—can rival diamonds in brilliance when cut to perfection.
Not all gemstones display fire
Opaque stones like jade and turquoise lack this characteristic entirely. These stones do not allow light to pass through them, meaning they do not exhibit dispersion (the rainbow-like flashes of light) at all. Dispersion relies on transparency and the ability of light to refract within a material. In coloured gemstones, the inherent hue may overshadow or mix with the spectral colours produced by dispersion, making the fire less distinct, but still complementary to the gem’s overall visual appeal.
Choosing sapphires with fire
Sapphires may not be known for the dramatic fire seen in diamonds or zircon, but they possess a stunning interplay of light and colour that is truly their own. The natural hues of sapphires—from classic deep blue to vibrant pink, yellow, and even the rare padparadscha—enhance their charm while subtly blending with their dispersion. This creates a mesmerising effect, especially in lighter-toned or colourless sapphires where dispersion is more visible.
When selecting a sapphire, focus on the quality of the cut, as this greatly influences how the stone interacts with light. Additionally, the setting can amplify a sapphire’s beauty; for example, a lighter metal like white gold or platinum can reflect light back into the gemstone, enhancing its brilliance.
So, now you know all about dispersion, are you ready to checkout our collection of sapphires?
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