What causes a diamond ring to get cloudy?

Most cloudy rings are externally dirty, and the cause is a stacked film of everyday products rather than any single event. Hand cream and sunscreen account for the largest share, particularly silicone-based formulas that bond to the stone surface. Cooking oils splash up from stove work and adhere to the prongs. Sweat, skin oils and dead skin cells fill the gap between the stone and the basket every day. Soap scum from shampoo and body wash adds a separate film during showers. Makeup transfers from the fingers each time the ring is put on or taken off. Together these build up within a fortnight on a daily-wear ring, and a single warm soapy soak clears all five at once.

Three internal causes produce permanent cloudiness that a soak does nothing for. Cloud inclusions, dense clusters of microscopic inclusions scattering light from inside the stone, show as a fixed haze concentrated in one area of the diamond. Strong fluorescence in a small percentage of natural diamonds, particularly under UV-heavy outdoor light, can create an oily or milky appearance even when the stone is clean. Some lab-grown diamonds contain metallic inclusions from the CVD or HPHT growth process that scatter light in the same way as natural clouds. A jeweller can identify which of these is at play under magnification, and the answer decides whether you are looking at a cleaning routine, a setting change or a stone replacement.