What can cause a diamond to appear cloudy?

A diamond can appear cloudy primarily due to the presence of numerous inclusions or a low-quality cut. Inclusions are internal or external flaws within a diamond that can disrupt light passing through it. These imperfections scatter light, which can lead to a hazy or cloudy appearance. Additionally, a low-quality cut may not reflect light optimally, resulting in a lack of brilliance and an overall dull look. Diamonds are admired for their sparkle, and when either of these issues is present, they can significantly detract from the stone's clarity and visual appeal.

In contrast, other factors listed do not directly lead to cloudiness in the same way. For instance, high fluorescence can sometimes make a diamond appear more vibrant under certain lighting, but it typically doesn’t cause cloudiness as it involves how the diamond reacts to light rather than obstructing it. Over-polishing, while it can affect a diamond's surface, usually does not cause a cloudy appearance; it may create a different kind of issue with how the diamond reflects light, but not cloudiness. Superior color grading indicates a high-quality color, which does not contribute to a cloudy look. Hence, the clarity and cut quality are paramount in determining whether a diamond appears cloudy.