Wrought iron has been a design element in furnishings for centuries, including in the creation of chandeliers and light fixtures.  Unlike cast iron, wrought iron is heated and then shaped by skilled blacksmiths into the desired form.  It is a very strong material, lasts forever, and can easily marry function and ornate design. 

 

Owning copper cookware was a sign of wealth.  Incorporating copper items into a chandelier made a statement.  Additionally, the artistic contrast of light (copper) and dark (wrought iron) with candlelight produced a strong visual effect.