In 1979 the biophysicist Philip Callahan photographed and scanned the tilma under infrared light and published his findings through the Center for Applied Research in the Apostolate. He reported no underdrawing, sizing or varnish of the kind expected in a conventional painting across the original figure, while also identifying several elements, the moon beneath the figure's feet, the gold rays, the supporting angel, as later additions painted over that original image by a different hand. The absence of underdrawing does not by itself establish how the image was made; infrared analysis alone cannot rule out lost or unconventional painting techniques, and Callahan's own background was in entomology and infrared photography rather than art conservation.
Working from an entirely different kind of evidence, the historian Stafford Poole's documentary study traces every known written reference to devotion at Tepeyac from the 1570s onward, and finds none that mentions the apparition and Juan Diego story until the Nican Mopohua's appearance in 1649. Poole also shows that the attribution of that text to Antonio Valeriano rests on a claim made by a different writer more than eighty years after Valeriano's death, not on anything Lasso de la Vega himself says about its authorship. Poole's findings concern the documentary history of the narrative, not the physical cloth, and the two investigations, physical and documentary, answer different questions without directly contradicting each other.
Sources The Tilma Under Infra-Red RadiationPhilip S. Callahan with Our Lady of Guadalupe: The Origins and Sources of a Mexican National Symbol, 1531-1797Stafford Poole