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Identifying Wood
#11
Quote:C14 dating isn't of the object itself but of the time period since it ceased taking in carbon atoms through photosynthesis....
Which is the heartwood. it is dead and no longer taking on Carbon.
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#12
To take that further, that's why sapwood (ie the living outer rings, usually 10-20 years worth) is the preferred material, always let the palaeobod with the microscope make the final selection....shame that's the bit carpenters tend to trim off....
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#13
Trees don't die in the all-in-one-go way mammals do.
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#14
Dinosaur Wrote:Currently engaged in large (and expensive) exercise finding the 'Neolithic Landscape' in an area where most of the pits etc have jack in them (he gets about, doesn't he!), so basically site-finding-by-C14ing-those-'undated'-features-everyone-always-ignores.....hopefully the rsults might embarass a few people.... }Smile

pdurdin - wood charcoal is dangerous stuff for dating, especially if you can't show that it came from the outermost few rings (ie the ones nearest to the date the tree was felled). 'Wild' trees can live for a very long time, that bit of oak they burned to produce your radiocarbon sample could have come from tthe middle of a 1000-year old tree, so would give you a C14 date 1000 years earlier than when the tree was felled. Even worse, the wood could also have spent another 1000 years in the roof of a church or the like before getting burnt, which would put you 2000 years wrong....

I've currently got a wierd one where I've got a c.1700BC pit (definite, well dated using other materials, multiple agreeing dates) where for some reason the wood charcoal derives from wood coming in at around 5500BC. Best guess is that they were drying out waterlogged old wood from an adjacent swampy area...take that as a warning. For exactly the same reason, always be suspicious of a lot of carbonised plant material (including wood charcoal) if you've any reason to think they may have been burning peat for fuel on your site - usually there are indicator plants that give the game away.

Try to avoid things like carbonised grain unless there's lots of it, single grains are especially suspect. They seem to fit rather neatly down worm-holes, and in my experience have been responsible for more duff dates than anything else. And be aware that carbonised hazelnut shell is near-indestructible and hence tends to turn up residually in later features. Ivory is dangerous since it could be mammoth ivory and turn out to be 100 000 years older than your Anglo-Saxon purse-ring....

C14 is a minefield!

If it's there, always go for carbonised residue on the inside of pots (stuff on the outside could be from the fuel, which could be eg old peat!) or articulated bone in preference to almost anything else. If bones were buried articulated it means the beast/person can only have died a short time before burial, which means that the carbon sample is likely to date from within a very few years of the context you're dating.

Here, here!

Oh and its been ages since I've lived in a pit
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#15
BAJR Wrote:Which is the heartwood. it is dead and no longer taking on Carbon.

Yep,
see Aitken, M. J. (1961) Physics and Archaeology, Interscience Publishers Ltd.


for many discussions of such problems...............is mentioned in loads of later stuff, this is the oldest reference to the old wood effect I could find.
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#16
If it wasn't for the old-wood effect sorting out C14 calibration curves would have been tricky.....
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