How was this painted 1500 years ago?

The 6th-century Christ Pantocrator icon conveys the dual nature of Christ through three distinct facial zones divided by a harsh, rigid vertical axis that prevents the two halves from blending emotionally. The viewer's left side embodies Christ's divine mercy and human incarnation, using soft geometry, relaxed lines, a gently arched eyebrow, and a wide, calm eye to project an approachable savior offering grace. In stark contrast, the viewer's right side represents his divine authority as the cosmic Judge, featuring a sharply tensed, raised brow, a piercing, constricted stare, and heavy, dark shadows that create a stern, formidable expression.