The ring is more of a doorway, with its rim as thick as an arm, a height of over a span, and a width of about a pace. It glitters in ever-changing colors.
This ter'angreal is what is used to test a woman to become a full Aes Sedai. Seven channelers must channel all Five Powers in a complex weave into it while the candidate enters the rings into a mirror world and must successfully perform one hundred weaves at the right times to pass.
Injury and death can occur within the rings, and a person can also simply not emerge from the ter'angreal.