Gold Kryptonite permanently removes superpowers from kryptonians.
Superman uses Gold Kryptonite to remove the powers of criminal Kryptonians inside the pocket universe.
In the movie Superman II, Superman steps into a chamber inside the Fortress of Solitude to have his superpowers removed.
This chamber must have been powered by Gold Kryptonite.
Jer-El removes Clark Kent's superpowers in an episode of Smallville.
Maybe Jor-El accomplished this using some Gold Kryptonite somewhere off camera.
Scientists have measured the effective range of Gold Kryptonite to be between 2 feet, and 20 feet.
Gold Kryptonite: 1/2 inch (1.27cm)
Lead Case: 3.75 inches x 2 inches x 3/4 inch (9.525 cm x 5.08 cm x 1.9 cm)