The jewelry manufacturers often use ultrasonic cleaning tanks which are a mixture of ammonia and detergent with ultrasonic agitation to provide faster cleaning process.Mostly jewelry stores now sell small ultrasonic cleaning domestic, but experience has shown that it is equal to the heat Soap water method and no more effective.
It is very hard to damage diamonds due to their hardness, but take great care that two do not rub together as they can scratch and cause abrasion to each other. Caked on grease and other dirt on the backs of the stones should be removed with warm soapy water and an old toothbrush, rinsed and dried with a lint free cloth. Also make sure that your diamond jewellery is stored in a jewellery case and individually wrapped.
Gemstones should be treated in the same way as diamonds. But take care when cleaning any sort of stone set jewellery that you do not do this in a washbasin or sink as if any stones loosen they will go straight down the drain.