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Thanks Mike,A further two observations/questions: 1. do you think the remains are raw wood burnt for the first time? Or raw wood charcoalified deliberately, and then ‘reburnt'? If it was a ‘charcoal’ fuel fire, as opposed to a raw wood one, that might explain things. Since it’s the BA - and metal processing of all sorts went on (lower temp things like Pb, Ag, processing etc - all seem to use charcoal too, not just bronze (or, later iron). These kinds of small scale metal activities can sometimes leave no trace at all archaeologically, except if you do a micromorph study (papers from Silchester give an example of small scale metal working discovered this way, but not evident in the archaeology).2. Your birch observations fit entirely with the Specific Gravity - calorific potential differences. Oak and beech have less water, are more dense (higher specific gravity), and structurally a lot more resilient as charcoal. Your hazel is still interesting!Regards, Robyn.
Dr Robyn Veal
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Affiliate researcher,
McDonald Institute for Archaeological Research, Department of Archaeology,
Fellow and tutor, Hughes Hall
University of Cambridge.
Honorary research associate, University of Sydney
www.robynveal.comOn 19 May 2016, at 9:50 am, Mike Allen <[log in to unmask]> wrote:Thank you for that - very useful, especially helpful.I often have hazel and charcoal in assemblages and the charcoal we have from our South Devon sites is interesting in the lack of hazel in view of its high preponderance in the local pollen spectra. Selection is something we have considered, but burning is small BA firing events where elsewhere in the region we have a good spectra of the local woods (ie we would expect both hazel and oak). The archaeologists feels that these burning events (associated with non-funerary cairns) parallel other BA general firing (rather then specific kilns/ovens) and they cant see a reason for specific selection. Other features elsewhere have much more defined and purposeful firing pits where indeed control of fire and heat and selection of wood (oak) is represented in the charcoal.My unscientific bonfire observations (7 records) of burning wood from 1.7cm to 12cm diameter, has show hazel and birch to be preserved less well in charcoal lumps in the resultant fire, but oak (and beech) to be more common as charcoal - and these are disproportionate to the wood proportions burnt on the fire. The fine ash is unidentifiable, but the small whitened fragile charcoal lumps (ie nearly ashed) were predominantly (76%) birch and hazel as opposed to oak and beech (excluding other garden bush and pyracantha etc.)MikeOn 19 May 2016 at 08:17, Robyn Veal <[log in to unmask]> wrote:Dear Mike,Thank you for an interesting question. I would suggest most charcoal specialists' experience in the lab is that hazel is not much weaker than oak (as charcoal). The concept of ‘higher temperature burning oak’ vs ‘lower temperature hazel’ is somewhat confusing. You possibly mean calorific potential (heat value inside the wood), which is slightly higher for oak than hazel (only slightly), a proxy for this is density. A fire burns at a range of temperatures, depending on position in the flame, and contact with air, ash present and other factors, (particularly structural, as well as how dry the wood is), and but all the wood in say the central part of a fire will reach roughly the same temperature, regardless of the CP of any woods present. That your hazel is not preserved will be something to do with its condition beforehand (for example, relative dryness, size of branch). Bigger branches take longer to dry out, and longer to ignite and burn. Also the structure of oak is more ‘closed’ than that of hazel (but again, not by much). Smaller branches have more of their wood in contact with the fire, and therefore greater ignition surface, greater contact with oxygen, and once a fire reaches a good temperature, smaller branches, (most other things being equal), burn faster, and more to completion.Eleni Asouti’s Charcoal analysis web has a good overview of charcoal preservation pcwww.liv.ac.uk/~easouti/Other things of interest are books on fire and how it behaves - e.g. Fire on Earth, an Introduction, 2014 ( A Scott et al), and a good chapter by Dehaan, J, ‘Fire and Bodies’ in The Analysis of Burned Human Remains 2008 (ed by Schmidt, C and Symes, S). Deehan is a forensics expert who explains exactly how fire behaves in every aspect (the human remains part is incidental, this is also a very good book in general).We do very often see oak and hazel mixed together in many UK and European archaeological deposits. Of course we all know oak is the commonest taxon in the UK, but your note reminds us that representation in the archaeology is another thing; as for pollen, the % of wood taxa in archaeological charcoal doesn’t represent that originally present, nor necessarily the relative proportions of those fuels in the forest. Much has been written about this!For an English source, Phil Austin at UCL has carried out a lot of local experimental burning of fires mixed woods under controlled conditions, and you may like to contact him for more info.And - it could just be selection!Regards, Robyn.
Dr Robyn Veal
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Affiliate researcher,
McDonald Institute for Archaeological Research, Department of Archaeology,
Fellow and tutor, Hughes Hall
University of Cambridge.
Honorary research associate, University of Sydney
www.robynveal.comOn 18 May 2016, at 9:20 pm, Mike Allen <[log in to unmask]> wrote:I have sites with open oak and hazel woodland in the pollen on a current upland heath. The charcoal from non domestic and non funerary and no industrial activity is nearly all oak? Where is the hazel? We have ne reason to thing that this is 100% selectionCould the high temperature burning oak, mixed with hazel in a fire results on oak charcoal, but just hazel ash (that what happens on my bonfires)?Mike
--Dr Michael J Allen, MCIfA, FLS, FSA
AEA: Allen Environmental Archaeology
Tel. 07828 103454 website at www.themolluscs.com
and Visiting Research Fellow in Environmental Archaeology, Bournemouth UniversitySeries Editor: Prehistoric Society Research Papers (http://www.prehistoricsociety.org/)Series Editor: Oxbow - Studying Scientific ArchaeologyVice President: Conchological Society of Great Britain & Ireland (http://www.conchsoc.org/)CSCS card holder (CRO)
--Dr Michael J Allen, MCIfA, FLS, FSA
AEA: Allen Environmental Archaeology
Tel. 07828 103454 website at www.themolluscs.com
and Visiting Research Fellow in Environmental Archaeology, Bournemouth UniversitySeries Editor: Prehistoric Society Research Papers (http://www.prehistoricsociety.org/)Series Editor: Oxbow - Studying Scientific ArchaeologyVice President: Conchological Society of Great Britain & Ireland (http://www.conchsoc.org/)CSCS card holder (CRO)