In this matter it is needful to speak with diffidence; for the sketches of our master are so widely scattered that few students can have examined the whole of them; and photographic reproductions, however admirable in their fidelity to outline, do not always give decisive evidence regarding the materials employed.
One thing seems manifest.

Michelangelo avoided those mixed methods with which Lionardo, the magician, wrought wonders.

He preferred an instrument which could be freely, broadly handled, inscribing form in strong plain strokes upon the candid paper.

The result attained, whether wrought by bold lines, or subtly hatched, or finished with the utmost delicacy of modulated shading, has always been traced out conscientiously and firmly, with one pointed stylus (pen, chalk, or matita), chosen for the purpose.

As I have said, it is the work of a sculptor, accustomed to wield chisel and mallet upon marble, rather than that of a painter, trained to secure effects by shadows and glazings.
It is possible, I think, to define, at least with some approximation to precision, Michelangelo's employment of his favourite vehicles for several purposes and at different periods of his life.