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, however the way steel is created binds the nickel molecules in such a way that the chain tends to not cause a reaction for most people with skin sensitivities. (Yay chemistry!) Even so, those with nickel allergies very occasionally cannot wear stainless steel. If you've worn other stainless steel jewelry without issues, then Rebeca Mojica Jewelry items should also be fine to wear. If you cannot wear steel, feel free to reach out to see if other options are available.
Composition: Iron: approximately 69% Chromium: 19%; Nickel: 9.25%; Magnesium approximately 2%; Silicon: 1%; Carbon 0.08%; Phosphorous 0.045%; Sulfur: 0.03%