Within the stratum granulosum begins a process called

The right answer is keratinization.

Keratinization defines a process by which living epidermal cells of the granular layer are transformed into dead squamous cells. It is a keratogenesis that induces keratin, a form of cornification.

The cells are filled with keratohyalin and cytokeratin, their nuclei degenerate and their membranes harden due to the addition of a protein on the cytoplasmic surface, involucrin.