Most pieces currently available are aluminum or stainless steel. By special request I work with many other metals, including sterling silver, gold-fill, copper, brass, bronze, niobium and titanium.
Aluminum - Most people—even those with metal sensitivities—report no reaction to aluminum, especially anodized aluminum. It is widely accepted that aluminum is very poorly absorbed through the skin, so you do not need to worry about metal toxicity.
Over time, aluminum will corrode slightly, losing a bit of shininess. It stops this process once its surface layer (very thin) has corroded.
Composition: Aluminum: 92.9 - 95.3%; Magnesium 0.8 - 1.2%; trace amounts possible of Chromium, Copper, Iron, Silicon, Zinc Manganese, Titanium
Stainless Steel - Steel lasts pretty much forever and does not tarnish.
Stainless steel contains nickel, so those with nickel allergies sometimes cannot wear stainless steel. However this varies greatly from person to person. If you've worn other stainless steel jewelry without issues, then Rebeca Mojica Jewelry items should also be fine to wear.
Composition: Iron: approximately 69% Chromium: 19%; Nickel: 9.25%; Magnesium approximately 2%; Silicon: 1%; Carbon 0.08%; Phosphorous 0.045%; Sulfur: 0.03%