It doesn't matter how careful you are when wearing your favorite diamond earrings, or how little you are wearing them: at some point they will be full of dirt, full stop. The diamond's sparkle seems to be gone and tiny, little dark pieces will be somehow visible in the smallest cavity of your pave setting (yuck).
This is the sign that the time to use an ultrasonic machine has arrived.
Although an ultrasonic machine is very good at removing the filthy dirt from even the smallest cavity of your pieces, it doesn't do anything about the tarnish/oxidation your jewels may have, and this is a very important point to keep in mind.
I found the ultrasonic machine to be so convenient that if you have a lot of jewellery (but not only that, they work even on glasses, watches, coins, makeup brushes, or any plastic or metallic parts that could go into the water.. I read someone is using them as a Guinness Surger Unit, whatever it is) it's a little cheap gadget worth having.
How to use one: fill the tank with water and a specific detergent (keep reading), place your pieces inside (they need to be submerged by water) and start the cycle: in a few minutes by using high frequency and vibrations the machine creates bubbles that remove all the dirt from even the smallest cavity of your pieces (try with pave jewellery). When you are happy with the result (it could take more than 1 cycle), let the pieces sit in the tank for about 10 minutes, to give the dirt the time to settle. Then take your pieces out, rinse them with water and dry.
I tell you: it makes a funny, a bit annoying noise, so don't be concerned by it, the cycles are very short anyway.
What to look for when you buy one: apart from the volume of water that they could contain (which really depends on your preferences, but for a domestic use a tank of 500-600 ml is more than enough), you need to check the temperature the machine reaches and the frequency. I would recommend a temperature between 30-80 celsius, an ultrasonic frequency between 37 and 40kHz, and an ultrasonic power (also called power consumption) of 50 watts.
What kind of detergent you need to use: you can buy an ultrasonic cleaner solution specifically made for the purpose, or you can put a drop of ammonia and a squirt of mild detergent (this works beautifully at least for jewellery).
Be careful: if in your jewellery the stones are set with glue (like in many costume jewellery), the ultrasonic machine is going to dissolve the glue and all the stones will pop out!
Is it safe with every kind of stone or with pearls? no really. The ultrasonic is very safe on "hard" stones like diamond, cubic zirconia, garnet, sapphire: but not so much with "soft" ones like lapis lazuli, pearls, mother of pearls, amber, opal.
And that's it!
Hope it helps,