A sphere of annihilation erases all matter except for artifacts. What exactly would the prerequisites of an artifact be for it to be an exception to the Sphere's effect?
From the sphere's description:
The sphere obliterates all matter it passes through and all matter that passes through it. Artifacts are the exception. Unless an artifact is susceptible to damage from a sphere of annihilation, it passes through the sphere unscathed. Anything else that touches the sphere but isn't wholly engulfed and obliterated by it takes 4d10 force damage.