The answer to whether a real diamond shines rainbow colors is yes; this optical phenomenon is known as “fire” or “dispersion.” Fire refers to the colorful flashes of light seen when a diamond is moved or exposed to a light source. This effect is a distinct characteristic caused by the way light is separated into its constituent colors as it passes through the stone. This component of a diamond’s sparkle adds a dynamic, multi-hued dimension to its appearance.
The Science of Diamond Fire
The presence of rainbow colors is a direct result of dispersion, an intrinsic property of the diamond material. When white light enters the diamond, the light beam slows down and bends, quantified by the diamond’s high refractive index of 2.42. Because white light is a blend of all spectral colors, each color travels at a slightly different speed through the dense material. This difference in speed causes the colors to bend at unique angles, effectively separating the white light into the full spectrum of a rainbow.
The degree to which a material separates light is measured by its dispersion value; a diamond’s value is approximately 0.044. As the separated light rays travel within the diamond, they reflect off the internal facets, similar to how a prism works. When these separated rays exit the top of the diamond, the individual colors become visible as distinct flashes of light. This prismatic effect transforms a simple beam of white light into the characteristic colored flashes known as fire.
Factors Influencing the Rainbow Effect
While dispersion is an inherent property of the diamond material, the visibility and intensity of the fire are heavily influenced by external and structural factors. The quality of the diamond’s cut is the primary variable determining how well the potential for fire is realized. Precise proportions and symmetry are necessary to ensure that light is correctly routed and reflected internally, maximizing the separation of colors upon exit.
If the diamond’s pavilion facets are cut too shallow or too deep, the light escapes before it can be dispersed and returned to the eye. The type of light source also plays a significant role in perception. Directional, concentrated light sources, such as a spotlight, tend to produce sharper, more noticeable flashes of fire than diffused lighting, like a cloudy day. The size of the facets and the observer’s viewing distance also modulate the visual effect.
How Diamond Fire Compares to Simulants
The rainbow effect in a genuine diamond is compared with the fire produced by common diamond simulants, such as Moissanite and Cubic Zirconia. Although simulants exhibit dispersion, their dispersion rates are significantly higher than that of diamond, leading to a different visual appearance. Moissanite, for instance, has a dispersion value of about 0.104, approximately 2.4 times greater than a diamond’s 0.044. This results in a much more intense, broader rainbow effect that some observers describe as a “disco ball” appearance, differing noticeably from the subtle flashes of a diamond.
Cubic Zirconia (CZ) has a dispersion value around 0.060, which is closer to a diamond’s than Moissanite, but it still produces a fire that appears slightly less defined. Moissanite is also doubly refractive, meaning light splits into two paths upon entering the stone, causing the internal facets to appear doubled under magnification. Diamonds, by contrast, are singly refractive, which prevents this doubling effect. These differences in the quality and quantity of the rainbow colors provide a practical way to distinguish a diamond from its alternatives.