Monday, April 14, 2014

Weighing The Shroud's 1988 Carbon Dating

The best book I've read on the Shroud of Turin is William Meacham's The Rape Of The Turin Shroud (Lulu, 2005). Meacham is an archeologist who's worked at the University of Hong Kong, and he's one of the scholars the Roman Catholic Church has consulted on issues related to the Shroud in recent decades.

His book is especially good on the subject of carbon dating. Since carbon dating is the primary argument raised against the large amount of evidence we have for the Shroud's authenticity, it's important that we rightly gauge the significance of the carbon dating that was done in 1988. Sometimes, people will object to the Shroud by citing the 1988 carbon dating alone, as if that dating by itself is sufficient reason to dismiss the Shroud. Harry Gove, a scientist who had a prominent role in developing carbon dating technology and bringing about the 1988 dating of the Shroud, suggested that the 1988 tests allow for only about a "one in a thousand trillion" chance that the Shroud dates to the first century (Relic, Icon Or Hoax? [Bristol and Philadelphia: Institute of Physics Publishing, 1996], 303). Gove even jokingly compares the possibility that the carbon dating is wrong to the possibility that "the law of gravity is in error" (305). But Meacham writes:

A more recent [carbon] date [for the Shroud] of whatever magnitude would also fail to settle the matter in view of the many possibilities of exchange and contamination over the centuries (variations in ambient atmosphere, boiling in oil and water, exposure to smoke and fire, contact with other organic materials) and the still unknown conditions of image formation, which affected the very cellulose of the linen….

Stuckenrath (1965:280) notes that the result [of carbon dating] is often more recent than expected and cites the wide divergence - from 1750 to 800 B.C. - of a series of 16 contemporaneous wood and charcoal samples…

As an archaeologist, I had used C-14 dating many dozens of times on excavated samples, and found that it does generally but not always give accurate results. Most other archaeologists and geologists that I know have the same view; a few are more skeptical of its reliability. The debate within the professions has been largely about its accuracy in settling fine-grained chronological questions, for example the question of whether a city was sacked in 703 B.C. rather than 751 B.C. Rogue results were normally discarded without any follow-up research, when it was abundantly clear that something was amiss, whether it was due to contamination or "old wood" or residual material from an earlier phase or intrusive from a later one. Such rogue dates are common in archaeology and geology and they are usually not subjected to any further detailed study. Instead, the normal practice would be to seek more and better samples, obtain new C-14 dates and review the overall clustering pattern indicated by the dates. Such has been my experience as an archaeologist: I have excavated, submitted and interpreted around one hundred fifty C-14 samples from Neolithic, Bronze Age and Early Historical sites. Of these dates obtained, about 110 were considered credible, 30 were rejected as unreliable and 10 were problematic. I mention this merely to inform the non-specialist that rogue dates are quite common in the general application of C-14 in archaeology. As fate would have it, I had dealt with more rogue samples than most other archaeologists, and furthermore had been involved with several C-14 labs in investigating why some of these samples yielded results which simply could not be correct in terms of their real calendar date….

It is important for anyone wishing to understand the normal archaeological use of C-14 to know that a single date or even a series of dates on a single object or feature is seldom if ever cited to answer important questions about the age of a culture or a site. To put a single radiocarbon date in the position of being the ultimate arbiter of the age of the Turin Shroud is a blatant departure from the way C-14 is normally used….

I doubted [prior to the 1988 dating of the Shroud] that a bulls eye date of first century would be obtained, but was cautiously optimistic that a result would indicate some antiquity for the Shroud, perhaps back to the 4th or 5th centuries, owing to some intractable contamination….

Prof. P. Betancourt and his colleagues remarked on the fact that 'so many [carbon] dates have proven to be useless because of contamination and other causes.'

And Prof. W. Woelfli, director of the Zurich lab where one of the Shroud samples was dated, remarked in a recent paper 'no method is immune from giving grossly incorrect datings when there are non-apparent problems with the samples…this situation occurs frequently [in carbon dating].'

(16, 42, 53-4, 59, 87, 101)

Meacham wrote nearly a decade ago. There have been some significant developments since then. In his book, Meacham discussed Ray Rogers' 2005 article that undermines the 1988 carbon dating results. Further research since then has corroborated Rogers' findings. For some examples, see here. A study published in 2010 by Marco Riani, et al., for instance, found significant heterogeneity in the section of the Shroud tested in 1988. In 2013, Giulio Fanti and some other researchers published the results of some dating tests they ran on alleged fragments of the Shroud. All of their dating methods showed a pre-medieval date.

On the other hand, Timothy Jull, a member of the University of Arizona lab that tested the Shroud in 1988, published an article in 2010 that cast doubt on Rogers' findings. In 2013, Hugh Farey wrote an article that discusses problems with the reweave hypothesis (the view that the section of the Shroud tested in 1988 contains some more recent threads woven into the original cloth during a repair, so that the more recent threads would distort the carbon dating).

Mark Oxley has written an article criticizing Jull's piece. For some initial reactions to Farey's article, see the thread here. In that thread, Thibault Heimburger says that he's noticed some problems with Farey's article and suggests that he'll be writing a response to it.

I think Jull and Farey make some good points that significantly weaken the reweave hypothesis. The reweave hypothesis still seems to be the best explanation of the evidence, but now by a smaller margin. We have to leave the door wide open to other possibilities.

Jull ends his article with a call for further carbon dating (and other testing), and Farey acknowledges that some of the findings by Rogers and others offer significant evidence against the 1988 dating. Though Jull and Farey stand by the 1988 testing, both acknowledge that some significant doubts have been raised about it, whether doubts in their own minds or others' doubts. The same can be said of Oxford's Christopher Ramsey, who, like Jull, was involved in the 1988 carbon dating.

So, we shouldn't just take into consideration the possibility of error in carbon dating in general, as outlined by Meacham above. We should also factor in the evidence we have for error specifically in the case of the Shroud.

Another factor to take into account is our ignorance about how the Shroud image was formed. In my quotation above, Meacham referred to "the still unknown conditions of image formation". Even if somebody thinks it's likely that the image formed as a result of Jesus' resurrection, as I do, we don't know much about the details involved. Whether the image was formed by some extremely rare naturalistic means or by something supernatural, we have to consider the possibility that carbon dating would be affected by it. Our ignorance of how the image was formed differentiates the Shroud from other cloths. There's a potential source of contamination that other cloths don't have.

We should also consider the evidence that suggests a date for the Shroud earlier than the timeframe given by the 1988 testing. For example, while discussing developments that have occurred since Meacham's book was published, I mentioned the research of Ray Rogers and Giulio Fanti and his associates. Rogers' dating argument based on vanillin and the dating methods of Fanti et al. support an earlier date for the Shroud.

And the Shroud figure seems to be Jesus (the timing of the image while the body was in a state of rigor mortis and before decomposition had set in aligns with the timing of Jesus' resurrection; the fact that the blood stains have been disturbed so little suggests some sort of paranormal removal of the body from the cloth; the high quality of the cloth is unusual for a typical crucifixion victim, but consistent with Jesus' burial by Joseph of Arimathea; the severity of the scourging is consistent with what John 19:1-5 tells us about Pilate's intent to use scourging without crucifixion, in contrast to the less severe scourging that would normally accompany a crucifixion; wounds around the top of the head are consistent with a crown of thorns; the legs aren't broken; the lance wound is rare among crucifixion victims; the man seems to be within Jesus' age range; etc.). But if the Shroud depicts Jesus, yet is medieval, then it's artwork or a forgery. A scenario in which a medieval crucifixion victim happened to be so similar to Jesus, without any intention of imitating Jesus, is tremendously unlikely. But if the Shroud is medieval artwork or a forgery, a lot of problems arise.

How would the artist or forger know how to portray a Roman crucifixion victim so accurately? Why would he repeatedly and accurately depart from how Jesus was portrayed in the large majority of medieval depictions (a nail wound closer to the wrist than the palm; wounds from a thick cap of thorns rather than a thin wreath of thorns; etc.)? Why are so many characteristics of the Shroud inconsistent with the interests of an artist or forger? Why would an artist or forger brilliant enough to produce such a masterpiece go about introducing his work to the world in such an ineffective manner? Geoffrey de Charny was a relatively low-level figure in the society of his day. The modest status of the Shroud around the medieval timeframe suggested by the 1988 carbon dating is incongruous with what an artist or forger brilliant enough to produce the Shroud would be likely to do with it. And why would an artist or forger include a close-up depiction of Jesus completely nude and uncovered on his back side, something that the vast majority of people seem to find objectionable even in the more sexually libertine cultures of our day (how much more so in a medieval context)? Why and how would an artist or forger include so many details that can't be seen by the naked eye (in an age without microscopes and other such devices)? Why would an artist or forger display his genius in the Shroud, but nowhere else? Why don't we see comparable displays of genius from the same source around the same time? Why is the Shroud such an isolated object that stands out so starkly from the medieval context?

The notion that the 1988 carbon dating alone equals or outweighs all of the evidence cited above for an earlier date is absurd. The 1988 dating of one small piece of the cloth, from such a poor area for that sort of testing, can't bear the weight that's so often placed upon it. I would argue that even if further carbon dating would produce the same or similar results, the evidence for an earlier date would still weigh more. Carbon dating alone, whether in its 1988 form or some improvement upon it, isn't enough. There has to be more. That's how good the evidence is for an earlier date.

Critics sometimes raise other objections to the Shroud, such as its lack of provenance prior to the fourteenth century and alleged medical inaccuracies. Meacham makes some good points in response to such objections in his book (e.g., 9, 44-5, 48). And those issues have been addressed many times in many other places. My intention isn't to address those issues in depth here. My point here is that critics had better have some very weighty arguments aside from the 1988 carbon dating, because the 1988 dating alone doesn't get the job done. Adding the other arguments critics have come up with so far doesn't get the job done either. But that's another issue.

You can read my review of Meacham's book at Amazon here.


  1. This is a long article, but I was wondering if you'd seen it and what your thoughts about it were:

    1. It looks like the bulk of the article is behind a paywall?

    2. However, here is a PDF of the same.

    3. Jonathan,

      I haven't read the article you've linked, but I briefly addressed Wilson's work in general in the comments section of a thread last year.