Unexpected Egyptian blue in Renaissance paintings: identification in works by Perugino and “Lo Spagna” in the Louvre collection

Abstract To reconstruct the history of Egyptian blue use in Renaissance painting, we conducted a systematic survey of Italian works in the Louvre collection, including both storage facilities and the Grande Galerie housing major Italian masterpieces. The investigation employed recently developed modified night-vision goggles to detect the characteristic infrared luminescence of Egyptian blue. Due to the presence of unshieldable sunlight in the Grande Galerie , we adapted the technique by utilizing the laser pointer integrated in the night-vision goggle as a marker to enhance pigment detection under ambient lighting conditions. Perugino's painting was subsequently relocated for detailed analysis under controlled lighting, while Lo Spagna's work was identified in the storage and directly examined using high-resolution imaging techniques. This study significantly expands our knowledge by adding two important artists to the three previously documented Renaissance masters (Raphael, Garofalo, l'Ortolano) who employed Egyptian blue pigment. The identification of Egyptian blue in Perugino's work is of particular historical significance as it predates its earliest known occurrence in the Renaissance by nine years. Given Perugino's role as Raphael's master, this suggests a potential transmission of this specialized technical knowledge as a workshop secret, from teacher to student within Perugino’s entourage, a hypothesis that warrants further systematic investigation across Perugino's broader oeuvre. Graphic abstract