Limestone on the Shroud

Much exaggeration has been written about the ‘dirt’ allegedly found on the feet, knees and nose of the image on the cloth, derived from no more than a grain of rock found on a single sticky tape sample taken by Ray Rogers in 1978. According to John Heller (Report on the Shroud of Turin), for example:

By the time the Gilberts had reached one knee, all the spectra were alike, except for the heel. 
“What,” wondered Eric, “is peculiar about the heel?”
He called in Sam Pellicori, who rigged the macroscope and slid it down the support system until it was right over the heel. He looked at it carefully under full magnification, and after a long examination turned to Eric and said, “It’s dirt.”
“What?” exploded Eric. “Let me look!”
Deep into and between the threads dirt particles could be seen.

Heller was not, of course, present in Turin in 1978, so his story is at least second-hand, and does not correlate with the paper published by Roger and Marty Gilbert (‘Ultraviolet-visible reflectance and fluorescence spectra of the Shroud of Turin’), who made the spectroscopic examinations referred to. Their diagram “showing locations of data points” indicates two places on the foot bloodstain, one of which could be the heel, three others on the cloth nearby, which would certainly not be expected to have similar spectra, and none at all anywhere else on the lower limbs. Their comparative graphs of different places show no qualitative difference between the heel and anywhere else, and there is no mention of dirt, rock or other particles in the entire paper.

John Jackson referred to “an abundance of microscopic dust or dirt” in the area of the dorsal foot, in an article he wrote for Shroud Spectrum International in 1988 (‘The Radiocarbon Date and How the Image was Formed on the Shroud’), but by the end of the century dirt was frequently referred to as having been found, and sometimes identified, on the knee and nose as well, although no sticky tape samples had been taken of either. Eric Jumper’s ‘A Comprehensive Examination of the Various Stains and Images on the Shroud of Turin’ contains no reference to dirt, and neither does Larry Schwalbe and Ray Rogers’s paper, ‘Physics and Chemistry of the Shroud of Turin.’ In an article for Archaeology magazine (‘The Shroud of Turin Through the Microscope’), Sam Pellicori wrote, “Visual observation of the heel area at 500 times magnification revealed the presence of the very fine yellowish particles suggesting dirt; the nose area may also contain dirt or residual skin material.”

There has obviously been minimal opportunity to characterise this ‘dirt.’ However in 1986, Joseph Kohlbeck, a microscopist at Hercules Aerospace, who described Ray Rogers as an old friend, was sent some samples for analysis. At the same time an expedition to Jerusalem by Eugenia Nitowski produced numerous samples, which Kohlbeck identified as “primarily travertine aragonite deposited from springs, rather than the more common calcite.” Perhaps surprisingly, Israeli geologist Amir Sandler says that, “Aragonite is not a common mineral in the Jerusalem area and the Judea Mountains, where the carbonate rocks are made of calcite or dolomite, or both. It is also absent in all soil types in this area,” but the two observations are not wholly contradictory.

In ‘New Evidence May Explain Image on Shroud of Turin’ (Biblical Archaeology Review, Jul/Aug 1986), Kohlbeck explains how he also identified the Shroud ‘dirt’ as travertine aragonite limestone, and then sent samples of the Shroud’s and Jerusalem’s limestone to Ricardo Levi-Setti, of the Enrico Fermi Institute of the University of Chicago, for electron probe analysis.

According to Kohlbeck, “these graphs revealed that the samples were an unusually close match, except for the minute pieces of flax that could not be separated from the Shroud’s calcium and caused a slight organic variation.” Unfortunately it is difficult to compare the analyses ourselves, as the diagrams accompanying the article are very small, very blurred, and “adapted by E. Nitowski.” Nevertheless, even a cursory inspection suggests that although the samples may match qualitatively, they are rather different quantitatively. This is important. For example trace elements in limestone typically include strontium and iron, so it is not surprising that they were found in both sets of samples. Geographical identity can, however, sometimes be determined by the relative proportions of these elements.

Interestingly, Kohlbeck mentions that the Jerusalem samples contained “small quantities of iron and strontium but no lead.” The significance of this is in a footnote: “These substances were detected by X-ray fluorescence. Lead was detected by the STuRP team on the Shroud fibers and by Joseph Kohlbeck in Jerusalem limestone samples. Dr. Levi-Setti, however, did not detect lead when he compared the mass spectra of Jerusalem limestone and Shroud fibers.” It is a pity that this notable discrepancy is not further explored.

The question of trace elements on the Shroud is complex. Morris, Schwalbe and London (‘X-Ray Fluorescence Investigation of the Shroud of Turin’) describe their findings with caution. They discuss calcium (up to 280µg/cm2), iron (≤60µg/cm2and strontium (4µg/cm2) at some length, and consider that, had there been any rubidium, yttrium or zirconium, their instrument would have been sensitive enough to detect it. However, “The most severe problem is with lead. We place an upper limit of 15µg/cm2 for lead in our data. Similar limits of 5µg/cm2 are estimated for copper and arsenic.” Also their apparatus “almost entirely precludes detection of silver, cadmium and tin.”

These findings contrast rather confusingly with a comparison of fibres carried out by energy dispersive spectroscopy in 1998 by Alan Adler, Russell Selzer and Frank DeBlase (‘Further Spectroscopic Investigations of Samples of the Shroud of Turin,’ in The Orphaned Manuscript). They list five fibres from non-image areas, four from water stains, four from scorches, two from serum, two from image areas, two from the backing cloth and two blood globs, together with three from the radiocarbon sample – although these were from the ‘riserva’ portion rather than the sample itself. Regrettably, although numerous FTIR graphs are published in this paper, there are no SEM photographs, and minimal microprobe analysis. What there is of this is confusing. A table entitled ‘Typical Weight % Element Composition Pattern of Shroud Fiber Types’ gives 93% carbon and 3.2% oxygen for non-image fibres. Calcium (0.4%) and iron (0.4%) are listed, but not strontium – or lead, or any other of the elements mentioned (but not found) by Morris et al., except copper (0.1%). On the other hand sodium (1.7%), chlorine (1.5%) and aluminium, silicon and potassium (all 0.1%) are listed.

The proportion of carbon is not credible. Flax is mostly cellulose, which is about 44% carbon and 49% oxygen. If any integrity is to be given to this table at all, we can only assume that the ‘non-image’ fibre was actually from a scorch. As such, it was contaminated by the water applied to extinguish the fire, which could have distorted the trace elemental composition.

Returning to the elemental composition of the limestone of the Shroud and of Jerusalem, as published in Kohlbeck and Nitowski’s BAR article. Here are the graphs for the Negative and Positive Secondary Ions found on the fibres, and they take a bit of interpreting, to say the least. Before attempting to analyse them, we could do worse than look at a paper by Levi-Setti (‘Progress in High Resolution Scanning Ion Microscopy and Secondary Ion Mass Spectrometry Imaging Microanalysis’, in Scanning Electron Microscopy, 1985, in which he includes negative ion ‘maps’ of some Shroud fibres, and the information, “the fibre surface is generally rich in Ca, distributed fairly uniformly with occasional concentration in the crumb-like fragments. The O distribution corresponds rather closely to that of Ca, although more sparse and particulated. Some Cl seems rather uniformly present. K and Na are very abundant in the surface fragments and occasionally anti-correlate with the Ca content. Some of the alkali-rich fragments also contain some Li, while the Ca-rich particulates also show a signal for mass 56 which we cannot separate between Fe and CaO.”

Here are the diagrams from the BAR article:

They are not very helpful, and do nothing to establish any difference in trace elements. The remark that they are “an unusually close match” is disingenuous, as what a “usual” closeness might be has never been established or demonstrated. They are all graphs of limestone, which is overwhelmingly made of calcium carbonate, so of course they resemble each other. However there are clearly peaks in the Jerusalem limestone graphs which are not present in the Shroud graphs and vice versa.

Analyses of specific limestones are hard to come by and harder to compare. A paper entitled ‘The Influence of Karst Aquifer Mineralogy and Geochemistry on Groundwater Characteristics: West Bank, Palestine’ in Water (2018), dealing with the aquifers north of Jerusalem, says “Generally, the trace elements with concentrations > 10 ppm include Sr (17-330 ppm), Mn (17-367 ppm), Ba (2-32 ppm), W (5-37 ppm), Cr (3-23 ppm), Zn (1.7-28 ppm), V (4-23 ppm), and Zr (1-22 ppm).” A paper dealing with French Limestones, ‘Compositional Characterization of French Limestone: A New Tool for Art Historians’ in Archaeometry (1994) analyses them in terms of metal oxides (presumably left over after heating?) of which the most prominent, > 100 ppm (apart from CaO and Fe₂O₃), are K₂O (910-4230 ppm), Na₂O (333-710 ppm), SrO (289-620 ppm) and MnO (36-123 ppm). Relating any of these to the elements allegedly present on the Shroud is not currently worthwhile.