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orion Orion: Castor oil impact on C14 tests

On Fri, 24 Oct 1997, fred cryer wrote:

> With regard to Ms. Lerner´s post:
> Greg Doudna pointed out some time ago that if one tests a sample more than
> once and arrives at radically different results, the laboratory
> automatically regards this as proof of contamination. Hence, if retesting
> by the same method of samples suspected of being outliers arrives at
> remarkably different dates from previous results, there will be a prima
> facie case for contamination.  

There are two very different senses of "outlier" here. When a single
article is tested several times, and we get a nice clustering of dates 
with some scattered outliers, naturally it makes sense to guess a
date at the middle of the bell curve. It makes sense because a single,
uniform piece of parchment by definition has a unique date of manufacture.
We have to choose one date, and it makes sense to choose the one supported
by the majority of tests.  

On the other hand, when a GROUP of articles shows "outliers", with
most articles' dates clustering in the middle, one simply does not have
the same kind of reason to reject the outliers. 

A single piece of  parchement can be made in either 100DC or 68AD, but not
both. Different articles could after all be of different age. 

Of course one could argue for a historical scenario in which the articles
are manufactured at the same time, and on basis of that call for rejection
of outliers. But this would only be as convincing as the scenario. For
people not impressed with the scenario there would be absolutely no
"scientific" grounds to reject "outliers". 

E.g., when dating the items stored in a library attic, there's no reason
to reject outliers in the second sense. The most natural assumption would
be that the articles grouped on the shelves are of different age. 

Thank you for the subsequent explanation of the tests,

					Best regards,	Asia Lerner

> Prof. Karl Anker Jørgensen, of the biochemistry department in the
Univ. of
> Århus (Denmark), tells me that the immersion times in the baths ordinarily
> used to clean samples for C-14 would be insufficient to remove castor oil
> contamination, which is why we have asked the curator of the National
> Museum to experiment with such procedures.
> Next, we are asking Dr. Rasmussen to make control tests by contaminating
> parchment samples of known date with both modern and ancient oils: this
> will provide controls on the nature and extent of various types of
> contamination.
> best regards,
> Fred Cryer