Comments about the Recent Experiment of Professor

A medieval artist originally used powdered ochre and applied it on a linen sheet laid over a body using a simple frottage technique. Only the most prominent features (elbows, hands, knees, upper parts of the legs and arms) were rubbed in such a way, otherwise large distortions would have been observed (experimental observation). Therefore the sheet was removed from the body and the image free-hand completed on the flat cloth. For the face, a bas-relief must be used. This is the original Shroud image as it was made and probably seen in the first decades or centuries. As red ochre is an earth pigment, it is “safe to assume that it should contain at least traces of non neutral compounds ...like humic acids, salts or organic impurities” (personal communication). Such impurities will cause with time a discoloration of the fibers. This discoloration results from the degradation (chemical etching) of the cellulose of the linen fibers. Meanwhile, the pigments particles which were not bound to the fibers fall down so that the image, as it is seen today, is almost only due to the discoloration described above.