Maintaining a clean diamond can sometimes be difficult, as jewelry settings can obstruct cleaning efforts, and oils, grease, and other hydrophobic materials adhere well to a diamond's surface. Some jewellers provide their customers with sudsy ammonia cleaning kits. Some other jewellers sell small ultrasonic cleaners. Home-based cleaning methods include immersing the diamond in ammonia-based or ethyl alcohol-based solutions, or even a solution of mild grease dissolving detergent and warm water.
Cleaning can damage some jewelry. For example, some class rings are coated with a dark pigment to reduce their shininess. Ultrasonic cleaning can remove this coating. Also, many gems (such as emerald and pearl) are soft or porous. Cleaning agents can erode or infiltrate these gems. Ultrasonic cleaning is also contraindicated for Opals, Tanzanite, Amber, and any gemstone that reveals a high degree of internal fractures.
Although it is not one of the 4 C's, cleanliness affects a diamonds's beauty as much as any of the 4 C's (cut, carat, color, clarity).
A clean diamond is more brilliant and fiery than the same diamond when it is "dirty". Dirt or grease on the top of a diamond reduces its luster. Water, dirt, or grease on the bottom of a diamond interferes with the diamond's brilliance and fire. Even a thin film absorbs some light that could have been reflected to the person looking at the diamond.
Colored dye or smudges can affect the perceived color of a gem. Historically, some jewellers' diamonds were misgraded due to smudges on the girdle, or dye on the culet. Current practice is to thoroughly clean a gem before grading its color as well as clarity.
Cleanliness does not affect the jewelry's market value, as jewellers routinely clean jewelry before offering it for sale. However, cleanliness might reflect the jewelry's sentimental value.
Other guides relating to jewelry and gemstone buying which you may find helpful are as follows:
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