Thanks to its chemical composition, cubic zirconia scratches more easily than a diamond. The stone's hardness is affected by the amount of calcium oxide the manufacturer used in the stone's creation; it's cheaper and easier for a manufacturer to use more than 10 percent calcium oxide, but this lowers the hardness of the stone. If your cubic zirconia is scratched, the best thing you can do is have the scratches sanded out by a professional gemologist and keep the new, scratch-free surface clean and protected.
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Consult a Gemologist
Visit a jeweler with a certified gemologist on staff. Have the gemologist look at your scratched zirconia stone and estimate how much (if any) surface area of the stone might be lost by grinding a fresh surface.
Discuss the possible scenarios for resurfacing your stone. The stone can be refaceted entirely if you want a different look. You can also ask for any sharp, bothersome edges to be ground down.
Ask the gemologist what size grit he would use to resurface your stone. Refaceting and resurfacing are done with a tool called a lap, using a particular grit size. Like sandpaper, the grit size refers to how rough the polishing surface is. A 100-grit lap, for example, is very rough and usually used to begin faceting a rough stone. The gemologist should give you a grit size between 325 and 3,000, depending on the depth of your scratch, in millimeters.
Make arrangements for the jeweler to polish and refinish your stone.
Keep the Stone Clean and Scratch-Free
Clean the refinished stone with jewelry cleaning solution and a soft toothbrush. Dip the toothbrush into the cleaning solution and gently brush the surface of the stone with soft strokes. Use the same amount of pressure you would to brush your teeth—don't grind the brush against the stone.
Dry the stone with a microfiber cloth before you put it away or wear it again—liquid can settle into cracks and crevices in the stone and dry there, hiding any new damage from view.
Remove your cubic zirconia jewelry while applying lotion, sunscreen or other oily emollients. Lotions will dry over the surface of the stone, leaving it dull.
Store your refinished cubic zirconia jewelry in fabric jewelry pouches to protect the stone's surface when not being worn.