Red Ochre and Vermilion on Shroud Tapes?

WALTER C. McCRONE
McCrone Research Institute
Chicago, Illinois

Although the 1988 carbon-14 date confirms a medieval origin, I reached that conclusion a decade earlier on the basis of polarized light microscopy1. The scientific controversy over the Shroud of Turin is unusual in its disparity of opinions, the one-sidedness of those opinions, and its nearly seventeen-year length2.

The Shroud of Turin, a linen cloth measuring 1.1 x 4.3 m., depicts two images, back and front views, of a naked crucified man. A group of scientists from the Shroud of Turin Research Project (STURP) spent five days and nights in Turin in October 1978 examining the Shroud. These scientists identified the Turin Shroud image as blood and oxidized/dehydrated cellulose3. I, instead, found no blood and established the presence of Fe2O3.xH2O and HgS corresponding to two common artist's pigments of the 14th century, red ochre and vermilion, with a collagen (gelatin) tempera binder. My microscopical studies were made on thousands of fibers and particles on the 32 Shroud tapes, each about 5 cm2 in area. These tapes retained surface particles and fibers from body-image, bloodstain, scorch, water stain and control areas.

To the unaided eye, the Shroud image is yellow to orange in most body-image areas, but red in blood-image areas. Microscopically, the image consists of yellow fibers and red particles; the red particles are more abundant in the red blood images, and the yellow fibers are the major colored substance in the body image. A careful microscopical survey of the 22 image tapes and 10 nonimage tapes shows, without exception, tiny red particles in body- and blood-image areas but no red particles on the fibers in the nonimage areas. The red particles require careful high-magnification light microscopy (600-1000x) to see and identify. The results of my studies are based on a total count of more than 8000 fibers on image and nonimage tapes. There are 10-26% yellow fibers in non-image areas and 29-72% yellow fibers in image areas.

The red particles are found on the fibers of all image tapes and have varying degrees of hydration, color, and refractive index (from about 2.5 to 3.01). These properties are characteristic of the artist's earth pigment, red ochre4. Common worldwide, this pigment has been used by artists for at least 30,000 years. The highest refractive index particles are hydrous, crystalline, highly birefringent hematite with indices of 2.78 and 3.01. The iron earth pigments are hydrous iron oxide ranging in color and refractive index from yellow ochre to red ochre depending on their history. This raises the refractive index and may result in crystallization of hematite, anhydrous Fe2O3. A significant proportion of the Shroud red ochre is hematite, thus accounting for the observed birefringence of many of the individual particles. The composition of the Shroud red ochre was confirmed both by electron microprobe and by X-ray diffraction5. The XRD data were obtained on single red particle weighing only <1 ng of which possibly 0.2-0.3 ng is pigment. Less than one-half of the pigment aggregate particle is crystalline (hematite and vermilion), hence the lines in the XRD pattern are very spotty and difficult to measure. The agreement with known hematite data is, nonetheless, convincing.

The blood-image areas show incrustations of red substance with indications of «spalling». Many loose particles aggregates, picked from the blood-image tapes, show red particles different in shape and in color from red ochre, but characteristic of the artist's pigment, vermilion (HgS). The most common vermilion pigment is ground mineral cinnabar. The other two are synthetic mercuric sulfides, one a modern wet-process product, and the other, a dry-process form first prepared by alchemists about 800 A.D. The chemical composition of this second red pigment was established by polarized light microscopy (PLM), by electron microprobe, by XRD, and microchemically. The PLM microchemical test requires wet ashing of one of the blood-image sherds to remove the organic binder, dissolution of the Hgs crystals in HIO3, and precipitation of a mercury mirror with metallic copper. All of this is done in a <100 m m diameter droplet on a copper penny as a source for copper. The XRD pattern identified hematite in this blood-image sherd and also showed the strongest lines for cinnabar, confirming vermilion. The research I have done shows varying ratios for the two different pigments, and proves there must have been two different paint applications, one a red ochre paint, and the other, a vermilion paint. The different paint sherds show varying amounts of red ochre relative to vermilion; this also supports the application of two paints. Futhermore, no vermilion pigment particles were observed on any of thousands of body-image tape fibers. It seems therefore reasonable that the Shroud was first painted and then the blood images were enhanced with a vermilion paint. The finding of HgS as an artist's pigment on the Shroud is highly significant. One might argue that Fe2O3 could be formed by blood, but it not possible to explain HgS as vermillion except as an artist's pigment. This I find incomprehensible nonsense. There is a very simple optical test that differentiates blood from red ochre or vermilion - the Becke line test for refractive index. Blood in any form or any organic derivative of blood has refractive indices less than 1.60. Red ochre and vermilion have indices nearly double that of blood, or nearly 3.0. Observing such particles with magnifications of at least 500 times differentiates instantly between these two possibilities, blood or red pigments, simply by focusing up and down. The high refractive index particles concentrate the illuminating light beam in the microscope like a lens and show a bright center as you focus above best focus. Blood or any low refractive particles show a dark center under the same focusing conditions. On examining thousands of red image particles on the Shroud tapes, I saw no low refractive red partides except rose madder particles and a few red silk fibers (from the Shroud wrapping cloth). None of the red image-area particles are soluble in hydrazine.

If the image on the Shroud is a painting, we must find a paint medium. On one tape I observed two fibers «cemented» together with a yellowed residue. Further examination by PLM at 200-400x shows paint residues on a number of fibers and very thin paint layers stripped from the fiber surfaces by the tape lifts. Therefore, I decided to test the image fibers for paint media (drying oils, gums, tempera) and blood using microhistological staining reactions. Tests for protein, using amido black as well as fuchsin, show thin stained paint residues, and occasional accumulations of paint on the image-area fibers from several image tapes. In many of these accumulations, red pigment particles are observed; the collagen is stained blue with amido black, and a hint of red pigment is still apparent within the sherd.

I think that the medieval artist6 thought about a shroud image in terms of a dark tomb. Instead of the usual portrait with normal light and shadow, he assumed that the image could only be produced by body contact with the cloth. This would explain the appearance of the shroud image and, as well, STURP's 3-D image contruction7. The artist painted directly on the cloth to image the body-contact points (forehead, bridge of the nose, cheekbones, mustache, beard, over the entire body, front, and back. See fig. 3-4). This automatically creates a negative image; areas that normally catch available light and appear bright, like the bridge of the nose, would instead all be dark.

I have also found a chapter entitled «Practice of Painting Generally During the XIVth Century» in an 1847 book, in which the author refers to the process as the English or German mode of painting faint images. «Among other methods, common on this side of the Alps, may be mentioned the cloth-painting of the English and Germans, and their peculiar process in tempera. ... In the Treviso record, ... mention is made of a German mode of painting (in water colours) on cloth. This branch of art seems to have been practiced on a large scale in England during the XIVth century ... Yet, after this linen is painted, its thinness is no more obscured than if it was not painted at all, as the colours have no body ... In the beginning of the XVth century, the ordinary tempera painting on cloth was certainly common in the Netherlands ... The peculiarity of the English method appears to have been its absolute transparency; ... As regards to English and German paintings on cloth, there can be little doubt that the thinness of execution for which they were remarkable, though it did not preclude gilding, was adopted with a view to durability. ... Vermilion, minium, lake, ochre, and 'face brown red', are mentioned in the Strassburg MS.»8.

Some STURP authors admit that the Shroud has protein Fe2O3, and Hgs in image areas, but attribute the protein to blood, the iron oxide to retting of the flax to form linen fibers, and the vermillion to contact of the Shroud with painted replicas. Many members of STURP, and others convinced of the athenticity of the Shroud, explain away the carbon dating result by invoking impure linen samples or a change in the date induced by the resurrection. They do not take into consideration, for example, the weight of the Shroud. The Shroud weights about 20 pounds (9 kg.); approximatley 40 pounds (18 kg.) of 20th century carbon contaminant (mold, mildew, bacteria etc.) would be required to raise the measured carbon date to 14th century. After multiple analisys, careful calibration, and statistical calculations, these are the dates given by the three laboratories of Oxford, Tucson and Zurich of the four samples carbon dated:

(Sample 1). Threads removed from the cape of St. Louis d'Anjou from the Basilica of Saint-Maximin, Var, France, known to date during the reign of King Phillipe IV (1290-1310). The average of 13 tests yielded a carbon-date of 1273 A.D.

(Sample 2). Linen from an early second century C.E. mummy of Cleopatra from Thebes dated by independent means to 60 B.C. The average of 11 measurements yielded a carbon-date of 35 A.D. (Sample 3). Linen from a tomb at Qasr Ibrim in Nubia, Egypt dated to the 11-12 centuries, A.D. The carbon-date, an average of 13 measurements, is 1093 A.D.

(Sample 4). The Shroud of Turin yielded a date of 1325 A.D. the average of 12 measurements at the three different laboratories.

The good agreement between the three laboratories and between the replicate measurements at each laboratory, the careful cleaning procedures, the experimental procedures, and the detailed calibrations and conservative statistical analyses of the data decribed in the 21-author Nature paper has earned the confidence of all objective scientists. As for others, there is nothing that can be said or done to convince them the 1325 date is undoubtedly correct. A second set of samples and a second carbon-dating will be a waste of time and effort even though it will certainly agree with the 1988/89 result.

The STURP scientists find no pigment particles at 20-50x (I used 400-2500x). They find no cementation of the fibers nor evidence of capillary flow. There is no way, at 50x, that anyone could recongnize the red particles as Fe2O3 and as red ochre or the HgS as a ninth century vermilion, and no way anyone could see that the pigment particles are cemented into an organic matrix and to the fibers. The amounts of pigments and medium on the body-image areas and some of the blood-image areas, barely visible microscopically, demonstrate that the absorption spectroscopy on 1-cm2 areas by Pellicori9 and others could not have detected them. Heller and Adler10 acknowledge the existence of Fe2O3 and Hgs in blood image areas. Accetta and Baumgart11 state that «Shroud blood comparison with known bloodstains show marked differences.» As I stand accused of misinterpreting (my) otherwise good data, I see that, at least, I am not alone.

NOTES

1 W.C. McCRONE, C. SKIRIUS, Light Microscopical Studies of the Turin 'Shroud', Microsope, 28, pp. 105-112, 1980. W.C. McCRONE et al., ibid., 29, pp. 19-38, 1981. See also W.C. McCRONE et al., Ann Arbour Science Publishers, I, 1973 and V, 1979.

2 See W.C. McCRONE, Judgement Day for the Turin Shroud, Chicago 1996.

3 L.A. SCHWALBE, R.N ROGERS, Anal. Chim. Acta 1982, 135, 3.

4 R. HARLEY, Artist's Pigments, London 1970, p. 122 and R.J. GETTENS, G.L. STOUT, Painting Materials, New York 1966, pp. 8, 25-26, 69-70.

5 W.C. McCRONE et al., Microsope, 29, p. 19, 1981

6 «cunningly painted as attested by the artist who had painted it», see H. THURSTON, «Memorandum of Pierre d'Arcis», The Month, 101, pp. 17-29, 1903. It is also quoted in I. WILSON, The Shroud of Turin, New York 1978, p. 231.

7 E.J. JUMPER, R.W. MOTTERN, Appl. Opt., 19, 1909, 1980.

8 C.L. EASTLAKE, Methods and Materials of Painting of the Great Schools and Masters, chapter V, London 1847, (reprinted New York 1960), pp. 94-112 and p. 448.

9 S.F. PELLICORI, Appl. Opt., 19, 1913, 1980, see also F. FEIGL, V. AUGER, Spot Tests in Organic Analysis, New York 1966.

10 J.H. HELLER, A.D. ADLER, Can. Soc. Forensic Sci., 14, 81, 1981. 11 J.S. ACCETTA, J.S. BAUMGART, Appl. Opt., 19, 1921, 1980.