Is the "blood" blood?
I don't think Heller and Adler are being treated very fairly by those who disagree with their conclusions. Neither in "Blood on the Shroud of Turin" (1980), nor in "A Chemical Investigation of the Shroud of Turin" (1981) do they suggest that they were predisposed to think the "blood" was blood before they began their investigations. Their identification of blood derivatives is essentially in two ways, by spectroscopy and by fluorescence. Although the 'Soret' band, distinctively present in the spectrum, and the porphyrins identified chemically are not specific to blood, the identification of porphyrins certainly narrows the field. Nether collagen nor albumin, for example, often quoted as possible pigment binders, contain porphyrins. Chlorophyll and urine do, as has been pointed out above, and perhaps some specific tests for these should have been tried in an attempt to rule them out. Iron, of course was found in abundance, which could as easily have come from ochre as blood, and there is insufficient qualitative data to distinguish between the two, but specific attempts to find any heavier metals failed, except in one small instance of mercury, which was initially missed altogether by McCrone and only found in a single instance by Heller and Adler. Although their conclusion at the end of their first paper is that there is "positive presumptive evidence" for the blood being real, they do spend some time admitting that neither the spectra nor the chemical identification had "absolute final confirmation." In their second paper, a standard test for bilirubins indicated that bilirubins were present, which, although again not wholly conclusive, does narrow the field further.
It is not impossible that the "blood" was created by concocting a pigment and a binder which, as it happens, fortuitously gives similar results, but I think if I were a forger it would be easier to dribble real blood on with some sort of pipette, wherever it seemed appropriate, or to dab it on to produce the "scourge marks."