Although most of the linen fibers removed from body and blood image areas of the "Shroud" by sticky transparent tape are well coated with well dispersed iron oxide pigment, there are numerous pigment particle aggregates that behave as though held together by an organic binder. Careful study of these aggregates shows positive evidence of such a binder. Additional study of many image fibers also shows evidence of an organic coating with imbedded iron oxide pigment particles. Histological stains used to identify paint media show negative results for drying oils and starch but positive results for tempera, a protein-base medium made from animal collagen, egg albumen or milk casein. Many pigment aggregates and many fibers from image areas were tested microscopically with amido black. Blue staining of thin fiber coatings, some blue patches of medium buildup and blue staining of pigment aggregates were observed thus confirming the presence of a tempera paint. Colorless fibers from image areas and all control area fibers stain only slightly or not at all. Additional tests for sulfur-containing amino acids present in eggs and milk but not collagen were negative, hence the medium observed on the "Shroud" is an animal tempera, a common paint medium during all of the past several thousand years. The image on the "Shroud", therefore, appears microscopically to have been applied as a red iron earth tempera. This pigment and this medium have been available for several millennia. The double full-length body image as seen today is known to have been copied in color by an artist in 1516 and impressed on a medallion even earlier, about possession of Geoffrey I de Charny in the 1350's. One must conclude that an artist has, at least, enhanced what would have been a far fainter original (authentic) image or he has produced the entire image.The date the artist did his work is therefore in the middle of the fourteenth century or earlier. The image on the cloth is extremely tenuous yet the only microscopically visible aspect of the image is a red pigmented organic paint vehicle. The entire image appears, therefore, to be the work of a skillful, well-informed artist.
Walter C. McCrone (Tue,) studied this question.