A Scientific Note About St. Juan Diego's Tilma

by Brother John M. Samaha, S.M.

            Various news reports in the past have suggested that the tilma (mantle, cloak) of St. Juan Diego depicting Our Lady of Guadalupe is phony.  One opinion was a fake made in Europe and brought to Mexico by Franciscans.  Another suggested the tilma was painted over the image of a dark-eyed Aztec goddess.  Both conjectures have been proven false.  The recent canonization of Juan Diego provides another opportunity to put these erroneous notions to rest for good.

            John J. Chiment teaches in the Department of Earth and Atmospheric Sciences at Cornell University in Ithaca, New York.  He is a paleontologist who teaches a course about determining the age, materials, and place of origin of art works.  Four years ago Dr. Gilberto Aquirre, a San Antonio, Texas, physician, requested him to join a team to examine St. Juan Diego's tilma portraying Our Lady of Guadalupe.

            Dr. Aquirre invited the team of scientists to examine the eyes of the icon.  Professor Chiment's special task was to comment on the age and composition of the fabric and pigments.  He visited the shrine in Mexico City twice, did tests on fibers at Cornell, and reported his findings to Dr. Aquirre, and to the Archbishop of Mexico City and his staff.

European Origin Theory

            Those who subscribed to the European origin theory said the tilma could not be a local Mexican product because it has lasted so long.  Local cloth made from woven cactus fibers lasts about a decade at most.  The tilma is almost five hundred years old, and has been on display in public daily.  People behind this theory said the tilma must be woven from European linen or cotton.

            Two fibers of the tilma were lent to Professor Chiment for testing.  These fibers had been removed from the outer edge of the tilma when it was stored during the Mexican Revolution.  The test results showed that the fibers did not come from native cactus plants, nor did they come from cotton, wool, or linen -- fibers that might have been used in Europe.  Rather, the tilma seems to have been woven from hemp, a plant native to Mexico.  Hemp is one of the strongest fibers known, and hempen cloth can last hundreds of years.  This could explain the tilma's remarkable state of preservation.

The Aztec Goddess Theory

            Those who proposed the Aztec goddess theory thought that photographs taken in ultraviolet light show an under painting (pentimento) of a dark-eyed, somewhat frightening woman.

            Professor Chiment reported that ultraviolet photography does not expose images in paintings.  Instead, ultraviolet light shows clearly the application of paint over another image.  This shows when an original has been touched up, usually with a clear varnish.  In this instance it appears that patches of varnish were applied over the eyes of the original image.  Conservationists often use these varnish patches to protect a surface. Today ultraviolet photography can help conservators remove the added varnish layer.

            To determine if there is really an under painting on Juan Diego's tilma, photographs need to be taken with light from the infrared part of the spectrum.

            These two theories about the European origin and the Aztec goddess regarding the tilma with Our Lady's image are simply incorrect.  Ordinary scientific tests have disproved them.

            Professor Chiment expressed hope that additional testing will be permitted.  He recommends an examination using neutron-activation analysis and x-ray fluorescence.  This might reveal details about the pigments of the image and the history of the tilma and could guide measures to conserve and safeguard the holy image.

The Real Significance of Juan Diego's Tilma

            The faithful cannot conceive of Our Lady of Guadalupe without St. Juan Diego's tilma. Because of this tilma she has been present to us for centuries.  Msgr. Virgilio Elizondo explains, "In the Indian cultures of that time, the tilma was the exterior expression of the innermost identity of the person.  By being visible on Juan Diego's tilma, Mary became imprinted in the deepest recesses of his heart -- and in the hearts of all who come to her."  Our Lady of Guadalupe is not simply an image on the tilma, as miraculous as this is.  She has become part her children's innermost identity.           


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