There are many different kinds of metals. Titanium is often used in medical implants because it is both light and hypoallergenic. Lovely material with which to work, but expensive. This is my source: www.theringlord.com. (Canadian too, so no import fees.)

My coif is made of aluminum in European 4-in-1 weave. The dress I'm working on is anodized (dyeing process) aluminum and EPDM (rubber) rings. Both are very good for most metal allergies.