C-14 Debate
from the Shroud Newsgroup:
alt.turin-shroud

Roger Sparks and William Meacham


This article is compiled from a series of postings that appeared on the Shroud Newsgroup, alt.turin-shroud. In it, Rodger Sparks, a carbon dating expert from New Zealand, and William Meacham, archaeologist and Shroud researcher from Hong Kong, debated some of the theories that have been proposed regarding possible inaccuracies in the 1988 carbon dating test results.


Subject: Re: C14 Dating of the Shroud
From: "Rodger Sparks"
Date: 1998/02/04
Newsgroups: alt.turin-shroud

From: William Meacham
Date: Wednesday, 28 January 1998 10:12
Subject: C14 Dating of the Shroud
Anyone who still believes that C14 dating has proven the Shroud to be medieval should be quickly disabused of that notion. See the most recent report by Garza Valdes re-printed on www.shroud.com concerning "bio- plastic coating" he found on Shroud fibers, in sufficient quantity to throw the date WAY off. This organic material would of course be younger than the linen itself and would not have been removed in pretreatment.

As one who earns his crust doing accelerator mass spectrometry radiocarbon dating, I have to say that I have a few problems with the Garza-Valdes & Mattingly theory. The difficulty is that the numbers don't seem to stack up correctly, and a theory that explains away the measured radiocarbon age of the Shroud has to have a quantitative basis since it basically is claiming that a number (the age) derived from an experiment is somehow wrong.

Let's start by noting that an organism growing on, and feeding on, the linen threads exclusively will simply re-shuffle the available carbon with no effect on the radiocarbon content. Hence the growth must incorporate carbon from an external source, and to produce an age shift like that postulated, that source must be the atmosphere, whether by photosynthesis or some other mechanism.

Accepting that, I can postulate three scenarios that illustrate the problems I have with the theory. As the starting point, assume that the "true" age of the Shroud is 2000 years, and further accept that the measured radiocarbon age (about 600 years) is a good estimate of the radiocarbon that was present in the samples measured.

1. Suppose that the bioplastic layer began at the time the cloth was made (2000 years ago) and has been growing uniformly ever since. Then the carbon in the layer will have an average radiocarbon age of about 1000 years. But there is no way you can combine a material with an age of 1000 years with another of 2000 years and get 600 years. So that scenario doesn't work.

2. Suppose that the Shroud remained growth-free right up to around the middle of the 20th century, when some process, or contamination, started the layer growing. The radiocarbon content of the atmosphere from around 1960 to the present is the highest it has ever been due to the atmospheric nuclear weapons testing in the 50s to the 70s, so the potential for contamination is correspondingly greater. But in order to shift a radiocarbon age from 2000 years to 600 years, about 20% of the carbon actually measured must come from the bioplastic layer. This is not negligible, and if regarded as a uniform layer around a cylindrical thread it represents an increase in the thread thickness of around 12%. I would have thought this would be detectable by someone with expertise in identifying textiles, and it also seems to conflict with the very slow growth rate that Garza-Valdes claims for the layer. In any case this scenario requires a fair bit of special pleading to have the layer starting to grow just when it would have the maximum effect. I find it unconvincing.

3. Suppose the bioplastic layer started growing at the time the existence of the Shroud became known (perhaps the exposure to the light and atmosphere could trigger the growth). That happened about 600 years ago (just the age given by the radiocarbon dating, but let that pass...). In this case the layer would have an average radiocarbon age of about 300 years. In order to shift the apparent age of the Shroud to 600 years, now around 80% of the carbon analysed has to come from the bioplastic layer, and only 20% comes from the linen. By my reckoning, the effect is to more than double the thickness of the threads, and I would expect them to become welded together. The matted appearance would be obvious to the most cursory inspection, and clearly does not describe the Shroud. Furthermore, the increase in weight of the Shroud would be quite apparent. So that does not work either.

These scenarios are simplifications, and more complex situations can, no doubt, be dreamed up. But those who want the Shroud to be 2000 years old still have the problem of accounting for the amount of radiocarbon actually found as opposed to the amount that should be there to give the desired age. The other problem is that measured value, 600 years, is the only fixed point available. Why, after all, does the Shroud have to be 2000 years old? The arguments against the radiocarbon age could just as well be used to justify an age of 1000, 3000 or 5000 years. Sometimes the simplest explanation is the best, and in this case accepting the radiocarbon evidence seems the most reasonable thing to do.

Rodger Sparks


Subject: Re: C14 Dating of the Shroud [long]
From: William Meacham
Date: 1998/02/16
Message-ID: <6ca999$7jt$1@nnrp2.dejanews.com>
Newsgroups: alt.turin-shroud

On Feb. 4, 1998, Rodger Sparks wrote:

[snip]
...Sometimes the simplest explanation is the best, and in this case accepting the radiocarbon evidence seems the most reasonable thing to do.

In this last sentence lies the rub. Translating the C14 age into a "real age" for the Shroud is not the simplest explanation in terms of the totality of evidence. No one makes an argument for the Shroud being 3000 or 5000 years old because the evidence from all the various studies that have been done on the object indicate that it is a real burial cloth with the image and bloodstains of a crucifixion victim. If it is not Christ, it is another crucified male who underwent the same kinds of tortures as mentioned in the biblical account, ie Roman-style crucifixion prefaced by scourging.

As an archaeologist with 25 years of experience using C14 for the dating of excavated samples, I know what most archaeologists do when C14 produces a date which conflicts strongly with other evidence from a site : 1) run more dates on different samples from the same context, and then 2) put the aberrant dates down to some unidentified problem (usually in a footnote to the site report if mentioned at all). This happens often in archaeology, even on sites and samples which were thought to be ideal for C14 dating. Very rarely is the problem of these individual aberrant dates ever resolved or even addressed. But over the years a whole host of difficulties have come to light with C14, e.g. modern living samples which give ages of hundreds or thousands of years, or centuries-old samples which give dates in the future. The causes of these phenomena are known, but in many other cases anomalous dates have not been satisfactorily explained. Caution is certainly in order when C14 results conflict with the lines of interpretation indicated by other evidence.

When I attended the 1986 conference in Turin for planning the C14 dating of the Shroud, at the invitation of the Vatican Academy of Sciences, I argued strongly for an extensive testing program (including various staining and microscopic studies) that would have examined the Shroud samples in detail for contamination. This was met with arrogant dismissal by 5 of the 7 radiocarbon lab heads in attendance. They ridiculed the notion that contamination could account for more than 1 or 2% of the C14 after standard pretreatment. Their stance was decidedly haughty then, and now shown to be dead wrong. The truth is that there are many possible sources of error which are not fully understood, and it simply behooves us to at least look for all the possibilities that we can.

Yes, it would take a lot of extraneous carbonaceous material to throw the date off by 1400 years, if contamination ALONE is the problem. Isotope exchange with materials on or in prolonged contact with the cloth is another very strong possibility, and one which is very difficult or impossible to evaluate or test for. But it probably is the cause of many aberrant dates obtained on samples from secure archaeological contexts.

Where does that leave us with the C14 dating of the Shroud? Still at stage 1 -- more samples need to be dated, from various places on the cloth, along with samples from the backing cloth whose age is precisely known. And of course all samples should be subjected to exhaustive screening and laboratory examination first.

My original post that elicited the reply from Sparks does, however, remain correct -- "Anyone who still believes that C14 dating has proven the Shroud to be medieval should be quickly disabused of that notion." The operative word is PROVEN. Nothing has been proven, and until more samples are taken and analyzed with the best scientific tools we have, nothing can be said conclusively about the age of Shroud.

William Meacham


Subject: Re: C14 Dating of the Shroud [long]
From: "Rodger Sparks"
Date: 1998/02/21
Message-ID: <6clbo5$tgi$1@reader1.reader.news.ozemail.net>
Newsgroups: alt.turin-shroud

William Meacham wrote in message
<6ca999$7jt$1@nnrp2.dejanews.com>...
On Feb. 4, 1998, Rodger Sparks wrote:
As one who earns his crust doing accelerator mass spectrometry radiocarbon dating, I have to say that I have a few problems with the Garza-Valdes & Mattingly theory. The difficulty is that the numbers don't seem to stack up correctly, and a theory that explains away the measured radiocarbon age of the Shroud has to have a quantitative basis since it basically is claiming that a number (the age) derived from an experiment is somehow wrong.

Remainder of original posting deleted. Meacham replies...

In this last sentence lies the rub. Translating the C14 age into a "real age" for the Shroud is not the simplest explanation in terms of the totality of evidence. No one makes an argument for the Shroud being 3000 or 5000 years old because the evidence from all the various studies that have been done on the object indicate that it is a real burial cloth with the image and bloodstains of a crucifixion victim. If it is not Christ, it is another crucified male who underwent the same kinds of tortures as mentioned in the biblical account, ie Roman-style crucifixion prefaced by scourging.

Point taken. But the point I was trying to make is that the radiocarbon data is the only hard evidence we have that indicates a specific time for the origin of the Shroud, as distinct from the more indirect data that suggests it might have an earlier origin, or is sufficiently indecisive to allow an interpretation of an older age, if that is what we want. That does not, of itself, make the radiocarbon results correct, but it raises the stakes for those who insist on the antiquity/historic significance of the Shroud.

As an archaeologist with 25 years of experience using C14 for the dating of excavated samples, I know what most archaeologists do when C14 produces a date which conflicts strongly with other evidence from a site : 1) run more dates on different samples from the same context, and then 2) put the aberrant dates down to some unidentified problem (usually in a footnote to the site report if mentioned at all). This happens often in archaeology, even on sites and samples which were thought to be ideal for C14 dating. Very rarely is the problem of these individual aberrant dates ever resolved or even addressed. But over the years a whole host of difficulties have come to light with C14, e.g. modern living samples which give ages of hundreds or thousands of years, or centuries-old samples which give dates in the future. The causes of these phenomena are known, but in many other cases anomalous dates have not been satisfactorily explained. Caution is certainly in order when C14 results conflict with the lines of interpretation indicated by other evidence.

I have no real quarrel with this paragraph. As a radiocarbon scientist (not, I must stress, an archaeologist) I am familiar with the problems that can arise when a radiocarbon date apparently conflicts with prior expectations. And as an occasional bearer of bad news, I am used to having a back full of arrows! Often, the best way to resolve such conflicts is to resample & redate, where this is possible. I can also say that in the great majority of cases the result of this is to reconfirm the previous result. We should remember that if radiocarbon dating (or any other technique) is to be really useful we must expect it to produce new knowledge that may well conflict with what was previously thought.

The examples of anomalous dates referred to do occur, and as pointed out they are mostly well understood - which means they do not pose a further problem. Sometimes problems do remain and we have to be prepared to either wait for a solution further down the track or start digging deeper to find out what is really going on. But I do not think that this is the situation with respect to the Shroud. The dates from the 3 laboratories do not pose any major difficulties (Garza-Valdes & Mattingly notwithstanding - see my original posting) except for those who are convinced that the Shroud -must- be 2000 years old.

When I attended the 1986 conference in Turin for planning the C14 dating of the Shroud, at the invitation of the Vatican Academy of Sciences, I argued strongly for an extensive testing program .... This was met with arrogant dismissal by 5 of the 7 radiocarbon lab heads in attendance. They ridiculed the notion that contamination could account for more than 1 or 2% of the C14 after standard pretreatment. ...

I do not know what transpired at the 1986 conference. On the face of it the suggestions made by Meacham seem quite reasonable, and if they were dismissed out of hand by others at the conference I can understand his feeling aggrieved. However, I can also understand representatives from radiocarbon laboratories being unwilling to accept the idea of a residual contamination of over 1% in a material such as linen after laboratory pretreatment. Indeed, that is the nub of my objection to Garza-Valdes' theory, where the required contamination is much greater than 1%.

Yes, it would take a lot of extraneous carbonaceous material to throw the date off by 1400 years, if contamination ALONE is the problem. Isotope exchange with materials on or in prolonged contact with the cloth is another very strong possibility, and one which is very difficult or impossible to evaluate or test for...

I am not sure what is meant by "isotopic exchange" as distinct from "contamination". If the suggestion is that 14C has preferentially migrated into the linen but not 13C and 12C, I have to say "no way!". The transfer of carbon into or out of the cloth is fundamentally either a physical or chemical process, and will include all isotopes. True, there may well be isotopic fractionation during such processes, but the extent of fractionation that occurs is nowhere near sufficient to cause an apparent shift of 1400 years in the radiocarbon age. The beauty of radiocarbon dating is that there are two stable isotopes, 12C and 13C, as well as the 14C. The ratio of 13C to 12C can be, and always is, used to determine the degree of isotopic fractionation and correct the 14C accordingly.

Where does that leave us with the C14 dating of the Shroud? Still at stage 1 -- more samples need to be dated, from various places on the cloth, along with samples from the backing cloth whose age is precisely known. And of course all samples should be subjected to exhaustive screening and laboratory examination first.

Well, OK. We can go through the process all over again, and maybe, if the Vatican agrees, that is what will happen. If I were a betting man I would take a pretty safe wager on the result.

My original post that elicited the reply from Sparks does, however, remain correct -- "Anyone who still believes that C14 dating has proven the Shroud to be medieval should be quickly disabused of that notion." ...
William Meacham

I think we must agree to differ on this last point. Of course, at the end of the day reaching decisions on matters such as this involves making judgements, and there will always be differences of opinion on how to interpret the evidence available. I can only say that I feel comfortable with the judgement that the radiocarbon evidence we have gives us the best available estimate of the true age of the Shroud of Turin.

Rodger Sparks


Subject: Re: C14 Dating of the Shroud [long]
From: William Meacham
Date: 1998/02/16
Message-ID: <6ca999$7jt$1@nnrp2.dejanews.com>
Newsgroups: alt.turin-shroud

On Feb. 21, 1998, Rodger Sparks wrote:

William Meacham wrote...:
[.....]
the evidence from all the various studies that have been done on the object indicate that it is a real burial cloth with the image and bloodstains of a crucifixion victim. If it is not Christ, it is another crucified male who underwent the same kinds of tortures as mentioned in the biblical account, ie Roman-style crucifixion prefaced by scourging.
[...]
the radiocarbon data is the only hard evidence we have that indicates a specific time for the origin of the Shroud, as distinct from the more indirect data that suggests it might have an earlier origin, or is sufficiently indecisive to allow an interpretation of an older age, if that is what we want.
[...]
I am familiar with the problems that can arise when a radiocarbon date apparently conflicts with prior expectations. And as an occasional bearer of bad news, I am used to having a back full of arrows! ...We should remember that if radiocarbon dating (or any other technique) is to be really useful we must expect it to produce new knowledge that may well conflict with what was previously thought.

My problem with this argument is that it places the radiocarbon data in a special category, that of "hard evidence," as against the "soft" and more indecisive data that suggests the Shroud might be older. The words of W. Wolfli (director of one of the AMS labs which dated the Shroud samples) are appropriate to bear in mind here: "The C14 method is not immune to grossly inaccurate dating when non-apparent problems exist in samples from the field. The existence of significant indeterminant errors occurs frequently." The C14 measurement is another piece of data, but it is not in some special category by itself. It could be right or it could be wrong about the real calendar age of the Shroud. Other data which indicates an antiquity for the Shroud could, similarly, be right or wrong. Neither is more or less decisive.

I will cite three examples to illustrate this. In the first few years of C14 dating, a serious discrepancy was observed with samples from early Egypt, in that the C14 "ages" were too young by several hundred years, at least according to the established chronology of dynastic history. There were those in the radiocarbon field who argued that it was the chronology that "had to be wrong" as it was more subjective and more open to interpretation than C14. Later, it was confirmed that, lo and behold, the chronology *was* correct and C14 dates needed calibration.

Secondly, one of the strongest indicators that the Shroud is much earlier than 13th or 14th century is the nail wound in the wrist. The art historian McNair wrote: "I have studied hundreds of paintings, sculptures and carvings of Christ's crucifixion and deposition, from the 13th to the 16th centuries, and not one of them shows the nail-wound anywhere but in the palm of his hand." The first human remains ever discovered showing evidence of crucifixion were unearthed in Israel in 1968, and the wrist (radial) bone had clear evidence of damage by the nail.

Thirdly, the archaeological scientist Stuart Fleming wrote: "It is the medical evidence that we are certainly looking at a gruesome document of crucifixion which satisfies me that the Shroud is not medieval in origin." There are many individual components of this medical evidence.

Now, it is *possible* that a medieval forger broke all the artistic traditions of his era and guessed that wrist-nailing was the Roman style of crucifixion. And it is *possible* (at a very long stretch) that a medieval forger crucified some poor bloke and got a body imprint on the cloth in some unknown manner. But it seems more likely to me (as one who values C14 dating and has used it for more than 100 samples in the last 25 years) that something has skewed the C14 age -- either the trauma of the 1532 fire, or the contamination represented by the bio-plastic coating discovered by Garza-Valdes, or incremental carbon exchange over the years, or very skilled medieval re-weaving at the corner where the samples were taken.

Me: Yes, it would take a lot of extraneous carbonaceous material to throw the date off by 1400 years, if contamination ALONE is the problem. Isotope exchange with materials on or in prolonged contact with the cloth is another very strong possibility, and one which is very difficult or impossible to evaluate or test for...
Sparks: I am not sure what is meant by "isotopic exchange" as distinct from "contamination". If the suggestion is that 14C has preferentially migrated into the linen but not 13C and 12C, I have to say "no way!".

Is that "no way" as in "proven beyond any shadow of doubt," or "no way" meaning "that goes against our most cherished operating assumptions?" It would be re-assuring to know that the idea of C14 being perhaps slightly more mobile in some circumstances has been thoroughly investigated. We are after all talking about the *radioactive* isotope, and an occurrence of 1 in ten trillion or so atoms of C13 and C12. Reviewing the failure at Arizona to duplicate the experiments of Kouznetsov et al (see below), theoretical physicists Jackson and Propp wrote: "Our analysis of the Russian data requires that the attachment rate for carbon-14 is faster than for the other two carbon isotopes so that if the fire is quenched before all carbon isotopes regain their statistical balance, the linen is enriched with carbon-14, making its radiocarbon age appear too recent by centuries."

I would consider "contamination" as extraneous matter adhering to the fibrils, or even lodged inside the lumens of the cells, which at least in theory is removable by some physical/chemical means. The bio-plastic coating is obviously a contaminant. Whereas exchange means to me (a non-physicist) that the material of the sample (in this case the cellulose of the linen itself) has exchanged carbon with either the atmosphere or other substances.

The transfer of carbon into or out of the cloth is fundamentally either a physical or chemical process, and will include all isotopes. True, there may well be isotopic fractionation during such processes, but the extent of fractionation that occurs is nowhere near sufficient to cause an apparent shift of 1400 years in the radiocarbon age. The beauty of radiocarbon dating is that there are two stable isotopes, 12C and 13C, as well as the 14C. The ratio of 13C to 12C can be, and always is, used to determine the degree of isotopic fractionation and correct the 14C accordingly.

Kouznetsov et al, writing in the Journal of Archaeological Science (23:109-122) argue, very convincingly I felt, about the possibilities for carbon exchange during the 1532 fire and especially about how the C13/C12 ratio would NOT reflect this event. While their experimental work has not yet been duplicated, it deserves respect as a possible scenario. Once again, the Shroud poses unique problems: what other object of known or suspected antiquity has been burned in an event more than 1000 years after its possible origin, and dated by C14 several centuries later?

William Meacham


Subject: Re: C14 Dating of the Shroud [long]
From: "Rodger Sparks"
Date: 1998/03/05
Message-ID: <6dls4k$u0d$1@reader1.reader.news.ozemail.net>
Newsgroups: alt.turin-shroud
William Meacham wrote in message
<6d4p1b$3r4$1@nnrp1.dejanews.com>...
On Feb. 21, 1998, Rodger Sparks wrote:
William Meacham wrote ... :

[...]
the evidence from all the various studies that have been done on the object indicate that it is a real burial cloth with the image and bloodstains of a crucifixion victim. If it is not Christ, it is another crucified male who underwent the same kinds of tortures as mentioned in the biblical account, ie Roman-style crucifixion prefaced by scourging.
[...]

This thread is in danger of losing its focus. Let me sum up why I entered into the discussion in the first place:

1. Meacham has, as on previous occasions, listed several reasons why 14C dates need to be obtained, and interpreted, with caution. Much of what he says I can agree with in principle, but although these views are presented in the context of the Shroud, if taken at face value they imply that all radiocarbon dates are unreliable. This is not so. Most of the intensive labour that occurs in a radiocarbon laboratory is directed at avoiding the traps pointed out by Meacham - plus a raft of others as well.

2. Garza-Valdes and Mattingly have put forward a theory to discredit the Shroud dates that at first sight appears to have a degree of scientific plausibility. I certainly do not know that the existence of a "bioplastic layer" is not correct, and so I am not in a position to deny its existence.

However, the arguments of Meacham & Garza-Valdes suffer from the same flaw, in that they are qualitative arguments. There seems to be the belief that by simply postulating the existence of a "contamination" the 14C dates must be discarded. But the important question is -how much- contamination is present. If it is insufficient to significantly affect a radiocarbon measurement then it is irrelevant to the argument. The quantitative dimension is essential to this discussion. That is the essence of the problem that I have with the Garza-Valdes theory, and the objections I set out in my original posting have not been answered.

Side issues such as "isotopic exchange" are just red herrings. Isotope chemistry is a well understood science, and exotic effects caused by the 1532 fire should have been observed elsewhere by now. Radiocarbon dating of burnt or charred material is commonly done (notably charcoal). Appealing to the special nature of radiocarbon because it is radioactive leads us into the area of voodoo science. Keeping an open mind for new knowledge is one thing, but all new discoveries must account for what we already know. If the only way we can explain a particular phenomenon is by rejecting what has already been established without providing an acceptable alternative way of interpreting prior knowledge, then that explanation must be viewed with deep suspicion. From this point of view the Shroud of Turin and Cold Fusion have a lot in common.

I rest my case.

Rodger Sparks


Subject: Re: C14 Dating of the Shroud [long]
From: William Meacham
Date: 1998/03/10
Newsgroups: alt.turin-shroud
"Rodger Sparks" wrote on March 5, 1998:

Meacham has, as on previous occasions, listed several reasons why 14C dates need to be obtained, and interpreted, with caution. Much of what he says I can agree with in principle, but although these views are presented in the context of the Shroud, if taken at face value they imply that all radiocarbon dates are unreliable. This is not so.

In all such discussions I always reiterate that C14 dating is a very useful technique and that most dates are reliable. But the fact remains that some are not, for reasons unknown. The quote from Wolfli that I cited earlier bears witness to this fact, as do many instances in which C14 dates are contradicted by a host of other evidence. The Shroud is another case in point.

However, the arguments of Meacham & Garza-Valdes suffer from the same flaw, in that they are qualitative arguments. There seems to be the belief that by simply postulating the existence of a "contamination" the 14C dates must be discarded. But the important question is -how much- contamination is present. If it is insufficient to significantly affect a radiocarbon measurement then it is irrelevant to the argument.

Yes and no. The fact that there is now strong evidence of contamination which would affect the C14 date of the Shroud puts the interpretation of that date in a new light. When the date was announced it was claimed to be accurate and there was no question about its being off by "how much?" other than the usual statistical precision. The presence of an unknown and unmeasured component of the C14 age does indeed lead one to discard it. To me it makes little sense to argue along the lines that: "well, there is some unknown factor but it can't be so significant as to alter the date by x years." At this stage we simply don't know how much it might throw the dates off. It cannot be discussed in quantitative terms as yet but its presence has been demonstrated. It is relevant to the argument until it can be demonstrated that it is insufficient to significantly affect the radiocarbon measurement. The burden of proof has shifted, and the C14 dates can no longer be cited any sort of scientific "proof" that the Shroud is medieval; of course they never constituted such a proof in the first place.

Side issues such as "isotopic exchange" are just red herrings. Isotope chemistry is a well understood science, and exotic effects caused by the 1532 fire should have been observed elsewhere by now. Radiocarbon dating of burnt or charred material is commonly done (notably charcoal). Appealing to the special nature of radiocarbon because it is radioactive leads us into the area of voodoo science.

It is useful to recall the earlier exchange:

Sparks: I am not sure what is meant by "isotopic exchange" as distinct from "contamination". If the suggestion is that 14C has preferentially migrated into the linen but not 13C and 12C, I have to say "no way!".
Me: Is that "no way" as in "proven beyond any shadow of doubt," or "no way" meaning "that goes against our most cherished operating assumptions?"

My question answered: a charge of "voodoo science" indicates that doubts are not allowed to be entertained about the basic assumptions. But there is very good theoretical reason and experimental evidence to lead one to consider the possibility. Further, molecular exchange of carbon atoms is known to take place in certain circumstances. If during the 1532 fire the Shroud exchanged carbon with either the atmosphere or some substance present on/in the fibers, its C14 age could be way off its real age. And the C13/C12 ratio would not necessarily reflect that such an exchange had taken place.

I closed the last post with the question: "What other object of known or suspected antiquity has been burned in an event more than 1000 years after its possible origin, and dated by C14 several centuries later?" It is pointless to argue that such exotic effects "should have been observed elsewhere by now." Maybe they should have been but haven't. Maybe the Shroud represents a unique case amongst objects dated by C14. It is true that charcoal and burnt material are routinely dated by C14, but the burning occurs at almost the same time as the sample's organic death. (For example, dead wood is collected by man and used for a fire 5000 years ago; if the fire caused any exchange it will not alter the C14 age of the charcoal left by the fire.) Or the burning occurs at a time later than the sample death but this fact is obscured. (For example, if the dead wood happened to be old wood already one or two thousand years old when collected, and the fire caused a significant exchange of carbon in it, we would not be in a position to recognize the exchange today. We would simply have a date that "seemed" off by a few hundred years, and there are many, many such dates!) So it cannot be said that the effect of fire on C14 dating has been ruled out through the routine dating of charred materials.

If the only way we can explain a particular phenomenon is by rejecting what has already been established without providing an acceptable alternative way of interpreting prior knowledge, then that explanation must be viewed with deep suspicion.

I agree entirely with this statement, and mutatis mutandis it sums up the attitude towards the C14 date of most who have studied the Turin Shroud -- from art historians to physicists to forensic pathologists. Of course, no real age has been *established* for the Shroud, just as it has not been established that fire cannot affect the C14 content of a sample. We must go with the best evidence that we have. In the case of the Shroud, the other evidence points very strongly toward an origin for the Shroud in antiquity, not in the 13th-14th centuries. In view of the 1532 fire AND the discovery by Garza-Valdes, it is the C14 age of the Shroud that must be viewed with deep suspicion, until another round of very careful and methodical testing is done.

William Meacham



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