Author of the Month


By Sean Hancock
December 2000

Sample Contamination

Mary Levine states, "Contamination refers to the existence of nonindigenous organics in the sample that were not formed together with the sample material" [17]

Many pictures from the early days of radiocarbon sample collection operations show scientific experts smoking cigarettes. Not very clever boys! As Renfrew points out - "drop a little ash onto your - soon to be chemically analysed - samples and you'll get the radiocarbon age of the tobacco plant that was used to make your cigarette" [18].

Although such methodical incompetence would never be tolerated today, archaeological samples still suffer from contamination. Known contaminants and how to deal with them are discussed in Taylor (1987). He groups major contaminants into four categories 1) physically removable, 2) acid soluble, 3) base soluble, and 4) solvent soluble. All of these contaminants, if not removed, can drastically influence the age determination the laboratory will come to for a sample [19].

H. E. Gove, one of the developers of Accelerator Mass Spectrometry (AMS), radiocarbon dated the Turin Shroud. The conclusion he came to was, that the fibre used to weave the shroud dated to AD 1325 [20].

Whilst Gove and his team support the authenticity of their findings completely many, for obvious reasons, believe that the Turin Shroud is older. Gove and his cohorts defend all of their criticisms expertly and if I had to choose a lane I would say that the scientific dating for the Turin Shroud is probably correct. Even so, the level of criticism that has been thrown at this particular project, illustrates how much can go wrong with radiocarbon dating and how suspicious some scientists are of it [21].

The samples, it has been argued, may have been contaminated by younger organic carbon; the cleaning techniques could have missed any modern traces of contamination. Indeed Robert Hedges of Oxford University has stated: "It is worth noting that small systematic errors cannot be completely ruled out" [22]. I wonder if Hedges would explain the discrepancies in the dates reached by the laboratories dating the Chelford wood as the result of "small systematic errors"? Again are we being fooled by heavy rhetoric, are we taken in by the inner confidence present in scientific reporting?

With regards to the official dating of the Turin Shroud Dr Leoncio Garza Valdes would certainly think so. All ancient textiles are coated in a bio-plastic film produced by bacteria that Garza-Valdes believes can throw radiocarbon dates way off [23]. In fact, he argues that the Turin Shroud could well prove to be 2000 years old as the radiocarbon date for it cannot be taken as the final word; other evidence has to be considered. Interestingly Gove (although he disagrees with Garza Valdes) conceded that his criticisms warranted further investigation [24].

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  1. Levine, 36
  2. Renfrew, 263
  3. Taylor, 41-43, Levine, 36
  4. Gove, 1999, 159
  5. Gove, 1999, 161-169
  6. Hedges,
  7. Garza-Valdes, The DNA of God (1999),
  8. Gove, Relic, Icon or Hoax, 308

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