Folco (./303) :
Je veux bien u calcul oué, même approximatif pour donner un résultat correct. Mais d'après WP, la datation est tout de même sujette à des changements conséquents lors d'un incendie (qui a manifestement eu lieu, plusieurs partie du suaire ayant cramé).
Alors allons y.
Le carbone est composé de beaucoup de carbone 12 (99
, d'un peu de carbone 13 (1 et d'une proportion minuscule de carbone 14 (de l'ordre de 10^-12).Le carbone 14 est radioactif, avec une demi vie d'environ 5700 ans.
Le carbone 14 dans la nature se désintègre peu à peu, mais il est recréé constamment par les rayons cosmiques, ce qui fait que sa proportion reste constante. (à de minuscules variations près, dues aux variations des rayons cosmiques, mais cela est pris en compte dans la méthode)
Appelons C la proportion de carbone 14 dans le carbone qu'on trouve dans la nature.
Prenons un organisme vivant. Tant qu'il est vivant, il échange du carbone avec la nature, en mangeant et en respirant. La proportion de carbone 14 dans son organisme reste donc égale à C. Par contre, une fois qu'il est mort, il n'échange plus de carbone, donc son stock de carbone 14 va petit à petit disparaître en se désintégrant.
Sa proportion de carbone 14 au bout de N années sera égale à :
C * a^N
où a = e^(-ln(2)/5700)
par exemple, au bout de 5700 ans, sa proportion de C14 sera
C * a^5700 = C/2, la moitié de la quantité de départ.
La méthode de datation consiste à mesurer la quantité de C14 restant, et à en déduire N. Pour le suaire, on a trouve N=689 à peu près, ce qui donne une date de 1988 - 689 = 1299, avec une incertitude de quelques années, qu'on peut calculer.
Maintenant, supposons que le suaire date en réalité de l'an 33, mais que, lors de l'incendie de Chambéry en 1532, des cendres se sont déposées dessus. Ça fait donc un ajout de carbone qui fausse la datation.
Supposons que pour un gramme de carbone du suaire, il y a X grammes de cendres datant de 1532.
En 1988, la proportion de C14 dans le suaire non contaminé devrait être
C * a^1955. (il y a 1955 ans entre 33 et 1988).
Et la proportion de C14 dans les cendres de 1532 doivent être
C * a^456. (il y a 456 ans entre 1532 et 1988).
La proportion de C14 dans l'ensemble { suaire + contaminant } est donc
( C*a^1955 + X*C*a^456 ) / (1+X)
Et il faut que cette proportion coïncide avec celle d'un suaire vieux de 689 ans, donc on a :
C * a^689 = ( C*a^1955 + X*C*a^456 ) / (1+X)
Il ne reste plus qu'à calculer X.
On simplifie par C : a^689 = ( a^1955 + X*a^456 ) / (1+X)
On fait passer 1+X de l'autre côté : a^689 + X*a^689 = a^1955 + X*a^456
On isole X : X = (a^689 - a^1955) / (a^456-a^689).
En faisant le calcul, on trouve :
X = 4.96
Autrement dit, pour un gramme de carbone du suaire, il faudrait 5 grammes de cendres. Le suaire devrait être un gros tas de cendres !
Donc une contamination ne suffit pas pour changer la date du XIVième au Ier siècle.
Ah non, tu apportes une mesure, c'est à toi (ou à ceux qui ont fait les tests évidemment) de montrer qu'elle tient la route.
Ah mais t'es drôle, c'est exactement ce qu'ils ont fait!
Avec trois labos différents, et trois échantillons témoins, et des résultats qui concordent tout à fait.
N'y a-t-il eu des prélèvements faits que pour cette étude ? Y en a-t-il eu faits à une autre époque ?Est-ce la seule datation au C14 de faite ?
Il y a eu d'autres prélèvement (par exemple McCrone a travaillé sur pas mal d'échantillons provenant de différentes parties du tissu) mais je crois que c'est la seule et unique datation au C14.
GUNNM (./304) :
Quand à l'ocre, il n'y en a aucune trace. T'as beau t'y accrocher fermement, il n'y a pas la moindre trace d'ocre sur le linge.
Je cite McCrone, qui est l'étude de référence :
Nearly 20 years ago the Catholic Church invited me to determine chemically what the image is on the Shroud of Turin.
I obtained 32 samples from the shroud: 18 from areas where there are images (both of a body and of bloodstains) and 14 from non-image areas (some from clear areas that served as controls, others from scorch and water stains caused by a fire in 1532). The samples were taken with squares of sticky tape, each of which exceeded a square inch in area and held more than 1,000 linen fibers and any materials attached to the shroud. They were excellent samples. I used standard forensic tests to check for blood. I found none. There is no blood on the shroud.
To determine what substances are present in the shroud images, I conducted tests based on polarized light microscopy. I identified the substance of the body-and-blood images as the paint pigment red ochre, in a collagen tempera medium. The blood image areas consist of another pigment, ver-milion, in addition to red ochre and tempera. These paints were in common use during the Middle Ages.
The paint on the shroud was dilute (0.01 percent in a 0.01 percent gelatin solution). I made up such a paint and an artist friend, Walter Sanford, painted an excellent shroud-like image (see photo at right and my book Judgement Day for the Shroud [Chicago: Mccrone Research Institute, 1996]. pp.145.149). Known as grisaille, the style of the painting, with its very faint, monochromatic image, was also common in the 14th century.
Based on the complete absence of any reference to the shroud before 1356, Bishop Henri of Poitiers's statement that he knew' the artist, the 14th-century painting style and my test results, I concluded in two papers published in 1980 that the shroud was painted in 1355 ('to give the paint a year to dry"). A third paper in 1981 confirmed these results with X-ray diffraction, scanning electron microscopy and energy dispersive X-ray determination of the elements present (iron, mercury and sulfur) in the two paints. Eight years after my published results, the carbon-dating results were reported as 1325 ± 65 year - thus confirming my date of 1355.
Ainsi que :
Any objective chemist would be convinced by my detailed articles and book, Judgement Day for the Turin Shroud, in which I argue that the shroud is a beautiful medieval painting. I am expert in using microscopical methods to identify the pigments, media and supports for each paint used in a painting. I have examined several hundred paintings, by artists from Giotto to Pollock, submitted to me by dealers, auction houses and collectors in order to authenticate them.
When I began my study of the 32 sticky tapes taken from body-image, blood-image, scorched and clean areas of the shroud, I looked for body fluids, especially blood. However, I immediately saw thousands of tiny red ochre particles in the image areas. The more I looked at these tapes, the more I became convinced that the image was paint. Subsequently, I found a second red pigment with the red ochre, but only in blood-image areas. I tested for blood by several recognized forensic tests (benzidine, luminol, Teichman, phenolphtbalein and sulfuric acid plus ultraviolet fluorescence). I might add that I am a member of the American Academy of Forensic Sciences and have worked on, and testified in court on, forensic cases.
I and an artist friend of mine have prepared shroudlike images on linen using diluted blood as a paint and examined sticky tapes from those images. There were no particles of blood, much less red particles. Dried blood is brown and present on my dilute blood-painted shroud tapes as a continuous brown gel-like smear. My colleagues at McCrone Associates used X-ray fluorescence and X-ray and electron diffraction on the samples, which confirmed my research in every respect.
I object 100 percent to all pro-shroud claims.
- Carbon dating-three world-class laboratories in the United States, England and Switzerland analyzed clean shroud samples and three other known-date cloths with agreement on all four cloths, and they did a good job of cleaning the samples. Only a few pro-shroud individuals disagree with their conclusion: 1325 +/- 65 years.
- Blood tests-I stand by my claim that there is no blood on the shroud. Anyone claiming there is guilty of wishful thinking and speaking from their belief in a first-century shroud.
- Mercury---the presence of mercuric sulfide as the pigment vermilion (in a form invented by alchemists in about 700 A.D. is proved microchemically, by X-ray diffraction and X-ray fluorescence. All of the seven blood-image tapes showed thousands of vermilion pigment particles dispersed on the linen fibers.
- Iron oxide (red ochre) as image- -neither Adler nor anyone else has shown that 90 percent of the iron is bonded to cellulose and is not present as colored iron oxide. This ludicrous statement is an out-and-out misrepresentation of the facts. Anyone making such a statement is either not a microscopist or is incompetent or lying. The explanation of the shroud image as due to debydrative oxidation of the cellulose is balderdash-absolutely impossible; 99 percent of the iron on the shroud is readily visible to a microscopist x micron-sized red particles of high refractive index bound to the linen with a dried gelatin paint medium.
- Pollen-Max Frei has been shown to have misled all of us with his report of 54 different species of pollen, all from the Near East, on the shroud.3 There were very few pollen grains an his tapes (I examined them very carefully).
- Three-dimensional images-I taught a noted Chicago portrait artist, Walter Sanford, to paint "shrouds" with convincing 3-D and negative images.
- History of the shroud-there is no credible evidence for the shroud before 1356, and the bishop at the time said he knew the artist who painted it. I can't go on. Some people believe so strongly in a real Christ's shroud that they 'see' anything that would be there if real. From my experience as a painting authenticator, the shroud is authentic-a beautiful and inspired authentic painting.