Diamonds do need the utmost care to keep them at their best.
A clean diamond not only reflects light better, but actually looks bigger than one that's been "dulled" by skin oils, soap, cosmetics and cooking grease. Diamonds have an affinity for grease and should be cleaned once every month to keep their fire at its brightest.
Prepare a small bowl of warm suds with any mild liquid detergent. Brush pieces gently with a tooth brush while they are in the suds. Transfer to a wire strainer and rinse under warm running water. Pat dry with a soft, lintfree cloth.
Make a half and half solution of cold water and household ammonia in a cup. Soak the diamond for 30 minutes. Lift out and tap gently around the back and front of the mounting with a small brush. Swish the solution once more, and drain on paper. No rinse is needed.