I think there are many who question the findings of the STURP team who carried out the scientific testing of the shroud and reported on it in 1981. One criticism was that the team did not include anyone with expertise on medieval paintings on linen and that the conclusions ruling out such a painting were therefore unreliable. Gesso was certainly used as a base for such paintings, applied with a knife rather than a brush, and would have prevented penetration of the fibres by any paint - an observation used by STURP to rule out painting of the image. The article seems to suggest that no one agrees with the findings of Walter McCrone, who found ochre and vermillion pigments in samples taken from the shroud but this doesn't seem to be true. Two STURP scientists later dismissed his findings and identified the blood to be genuine but they were not experts in forensic analysis of blood stains or of medieval pigments. There is evidence which fits with the shroud being a painted linen cloth of the 14th century which has faded and been damaged and contaminated by repeated handling. It is worth noting as well that there were quite a few shrouds around at one time all of which were venerated. The Turin shroud has survived whereas others have not for various reasons.