A diamond necklace should be cleaned every few months to keep it looking its best. However, you should clean it regularly if you wear it more often or see dirt, oils, or residues.
Use mild soapy water or a jewelry cleaning solution made especially for diamonds to clean a diamond necklace at home. Rinse the necklace well in warm water after gently cleaning it with a gentle brush or toothbrush, and then pat it dry with a soft, lint-free towel.
Consult an expert jewel if you are unsure or worried about cleaning.