Numerous pigment particle aggregates that behave as though held together by an organic binder were observed on linen fibers removed from the Holy Shroud of Turin. These aggregates and fibers from image areas were tested microscopically with amido black which confirmed the presence of a tempera paint. A simple microscopical test for sulfur-containing amino acid functional groups -- the catalytic release of nitrogen gas from sodium azide in the presence of iodine -- was negative indicating the tempera was of animal (collagen) origin. An artist has at least enhanced what would have been a far fainter (authentic) image or he has produced the entire image applied as a red iron earth tempera. See 18-839 and 18-841. -- AATA