Giardinoblu Jewels are in Bronze and Sterling Silver.• Bronze is a metal alloy and the fact that it turns the color with time also depend on how the alloy is made and what is contains. Our bronze don't turn in green, however we recommend to taking care of your jewelry periodically, so they always be bright and shine. Here's some practical tips.• Sterling Silver can shift its color turning to a warmer shade over time, everything you need is choose your favorite “caring ritual” in this page to keep your jewelry at best.You can also ask for a special Silver alloy with Palladium. This metal turns it's color much more slower then sterling silver keeping its bright for longer.