Wire is wrapped tightly around a knitting needle to form a coil. The coil is then slit on one side to make the rings. The size of the knitting needle determines the size of the opening of each ring. The gage of the wire determines how thick the ring is. Determining the size and thickness of the rings is crucial - different weaves require different sizes in order to create the correct tightness of the finished piece.
The wire I use is designed for jewelry making. It is copper with silver foil covering - the silver foil is available in many colors. It also has a coating that resists tarnish, so should never be polished. Polish, even toothpaste, is abrasive and can scratch or remove this protective coating, resulting in discoloration. A mild solution of dish soap or shampoo (no heavy scrubbing, please!), thorough rinsing, and patting dry with a soft cloth is recommended if cleaning is needed.