Patent ID: 7624594

Claim:
A manufacturing method of a magnetic recording medium substrate, comprising the successive steps of: performing inner/outer diameter processing to form an inner diameter bore in the magnetic recording medium substrate composed of an amorphous glass substrate of B 2 O 3 —Al 2 O 3 —SiO 2 —Li 2 O type; performing chamfering process to form a chamfer between inner/outer circumference side edge face and a principal plane of the magnetic recording medium substrate; polishing the inner/outer circumference side edge face and the chamfer; dipping the magnetic recording medium substrate in fused salt including sodium or potassium; and polishing the principle plane of the magnetic recording substrate, wherein the content of sodium and potassium at the surface area of the inner/outer circumference side edge face and the surface area of the chamfer is greater than a mean content of sodium and potassium of the magnetic recording medium substrate.