The underpainting has been done in casein. Casein paint is derived from milk, and is a fast-drying, water-soluble medium used by artists. Casein paint has been used since ancient Egyptian times as a form of tempera paint, and is still used today.
A short explanation of the painting subject:
Sophia, a feminine figure, analogous to the human soul but also simultaneously one of the Feminine aspects of God and the Bride of Christ. The Sophia resides in all of us as the Divine Spark. In Gnostic tradition, the term Sophia (?o?í?, Greek for “wisdom” refers to the final and lowest emanation of God.