Ingredients
1/2 oz. mild soap shavings
Mix first three ingredients in the water and boil until dissolved. Partly cool, and stir in liquid ammonia. Add enough water to make 2 quarts. When ready, place
jewelry in an enamel pan, cover with the solution and bring to a boil. Using a soft toothbrush or mascara brush, rub jewelry gently and rinse in hot water. Pat dry.
Here's another way to clean your diamonds: Place your diamonds in a
tea strainer and dip them into a pot of boiling water containing several drops of ammonia and a spoonful of soapflakes. Hold for a few seconds, then remove and rinse in cold ater. Soak for 5 minutes in alcohol, and finally rinse and pat dry.
Cleaning pearls:

Dampen a soft
cloth with
olive oil, then rub each pearl with the oiled cloth.
Cleaning silver jewelry:
Make a paste of lemon juice and baking soda. Brush it onto your jewelry with a toothbrush and allow to dry. Finally, brush it off and then polish it gently with a soft cloth.

Put your costume jewelry into a small container. Pour a little rubbing alcohol over the item and allow it to soak for three or four minutes. Remove it and wipe dry with a soft cloth.
or

Fill your bathroom sink with hot water and drop in a couple of denture tablets. Place your costume jewelry in and leave for a while.
Note: I wouldn't recommend using toothpaste because they sometimes contain abrasives that will scratch your jewelry.
Coating your costume jewelry with clear nail polish can be a good idea to protect the jewelry from exterior elements like soap, water, hairspray, cologne and your own body oils This will also protect your skin in case of a bad reaction to the metal.