Complex sentence: Costume jewelry (also called fashion jewelry, junk jewelry or fake jewelry) is jewelry that is made of less valuable materials, including base metals, glass, plastic, and synthetic stones, in place of more valuable materials such as precious metals and gems.
Split into simpler sentences: Costume jewelry (also called fashion jewelry, junk jewelry or fake jewelry) is jewelry that is made of less valuable materials. Other material that costume jewelry is made of includes base metals, glass, plastic, and synthetic stones, in place of more valuable materials such as precious metals and gems.