The Restorer Who Knew Every Brushstroke

In 2012, art restorer Dianne Dwyer Modestini spent over 18 months working on a damaged painting of Christ attributed to Leonardo da Vinci — the Salvator Mundi. She worked with magnifying loupes pressed to her eyes, studying each millimeter of the wooden panel. After thousands of hours, she could identify which brushstrokes were Leonardo's and which belonged to later, clumsy hands.…