What does smoke treatment do to an opal?

Smoke treatment for opals primarily serves to darken the stone's surface and enhance its play-of-color. This process involves exposing the opal to smoke, which creates a layer of carbon on the surface. This carbon layer contributes to a richer, darker appearance of the opal, allowing the vibrant colors within the stone to become more pronounced and visible.

The darkening effect is particularly beneficial for lighter opals, as it helps to provide contrast to the play-of-color, making the gemstone more visually appealing. Enhanced play-of-color refers to the way light interacts with the internal structure of the opal, resulting in the phenomenon of color flashes that can be seen as the stone moves in light. By improving the visibility of these colors through the smoke treatment, the overall aesthetic value of the opal is significantly increased.

The other options related to clarity enhancement, hardness improvement, or weight increase do not apply in the same way to smoke treatment. Clarity is typically managed through different methods, hardness tends to be an intrinsic quality of the mineral structure itself, and weight changes are generally not a direct outcome of smoke treatment. Therefore, the primary effect of smoke treatment focuses on darkening and enhancing the play-of-color in opals.