Dear Oliver and Miguel,
I can confirm that burning IS selective: some years ago we compared the
isotopic signatures of (archaeological, Holocene) wood and charcoal
samples, in a large data set (2541 charcoal and 1174 wood samples),
combined from the Groningen and Oxford 14C databases (Geophysical Research
Letters 21: 445-448).
This data analysis shows a 1 to 2 permil difference between wood and
charcoal, in my opinion caused by a shift in the cellulose-lignin ratio
during charring.
Best regards,
Gert Jaap

>Dear Oliver,
>Thank you very much for your help. The information I've collected so far is
>quite coincident with your 'five pence'. In principle, the isotopic
>signatures in the cellulose of the carbonized wood samples are only
>conservative (respect to the non-burned material) if some extractable
>cellulose remains in it. So, as you can see, using carbonized wood from
>archeological sites, does not seem very promising concerning the aplication
>of isotopic techniques.
>Regards,
>
>Miguel

>
>Dear Miguel,
>
>I think this would depend on the degree to which the wood is
>burned. I there is only ash left over, then I think the carbon that
>rests in it will not be representative of the whole sample. And I
>woudl guess that also to be true for samples that are only burned
>to a certain degree : as wood is not a very homogeneous material,
>burning might be selective and you might be left with a different
>siganture than you had before .. just my five pence...
>
>but I would be interested in any experiences on this subject


*************************************************************
Beware:  Delivery address (street name) has changed!!
*************************************************************
Dr. Gert Jaap van Klinken
14C AMS Laboratory
Max-Planck-Institut für Biogeochemie
PO Box 10 01 64
07701 Jena
Germany

Delivery (larger items), and visiting address:
Carl-Zeiss-Promenade 10
07745 Jena
Germany

Tel: (+49 3641) 643708/3806
Fax (+49 3641) 643710