Composite magnetic recording medium

A method for treating a glass hard disk substrate, comprising:

• obtaining a formed glass hard disk substrate;
• annealing the formed glass hard disk substrate to form an annealed glass hard disk substrate by ramping up the formed glass hard disk substrate to an annealing temperature, maintaining the glass hard disk substrate at the annealing temperature for a first amount of time, and cooling the glass hard disk substrate at a first cooling rate;
• and
• tempering the annealed glass hard disk substrate to form a tempered and annealed glass hard disk substrate by ramping up the annealed glass hard disk substrate to a tempering temperature, maintaining the glass hard disk substrate at the tempering temperature for a second amount of time, and cooling the glass hard disk substrate at a second cooling rate,
• wherein the formed glass hard disk substrate is one of a plurality of formed glass hard disk substrates forming a columnar stack of glass hard disk substrates;
• and
• wherein the step of cooling the glass hard disk substrate at the second cooling rate comprising cooling the stack of glass hard disk substrates by flowing air over an outer circumference of the stack of glass hard disk substrates at a first air flow rate and by flowing air over an inner circumference of the stack of glass hard disk substrates at a second air flow rate.