Found this bit of information on Wikipedia:

Costume jewelry came into being in the 1930s as a cheap, disposable accessory meant to be worn with a specific outfit. It was intended to be fashionable for a short period of time, outdate itself, and then be repurchased to fit with a new outfit or new fashion style. Its main use is in fashion, as opposed to "real" (fine) jewelry which may be regarded primarily as collectibles, keepsakes, or investments.