These double flare concave blue goldstone plugs have a wearable area of 3/8" between flares. Blue Goldstone is actually a type of glass that frequently gets lumped into the stone category. In traditional jewelry making, it's interchanged with semi-precious stone cabochons because it's such a striking material. The process to create goldstone was invented in 17th century Italy and remained a closely guarded for almost two centuries. Choose your size below.