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As a researcher on starch and an author of the book Ancient Starch Research, let me add my own perspective on the issue of preservation, which is something that I am very interested in understanding. I certainly don't take it for granted that every starch grain seen on the surface of stone tool or in sediment is necessarily 'ancient'; a case must be made by the analyst as to their reasons for interpreting the material as an archaeological residue. To that end I have published a few papers that specifically deal with the argument of starch preservation and more broadly on our understanding of what an organic residue actually is - if not contamination, as is often claimed. Most Recently I published a paper looking at residues on museum artefacts and discuss the preservation taphonomy of starch in that particular context. Barton, H. 2007. Starch residues on museum artefacts: implications for determining tool use. JOurnal of Archaeological Science 34: 1752-1762. In that study, I found that starch granules were often found in very different states of preservation on a tool surface. Some granules were heavily degraded by microbial activity - showing all the charactersitc forms of enzyme attack that the literature predicts and fits with expectations, however, many granules, from the same residue extraction were recovered in a perfectly good state of preservation. Apparently unaffected by enzyme decay. why? I suggest that the formation of an 'organic residue' - which must generally consist of some mixture of mashed up plant material, lipids, etc. dries rapidly and entombs some starches preventing access to microorganisms - some starches are not so protected and are degraded by all the mechanisms known to degrade starch. Sometimes these old starches have different visual properties to modern starch, and have been altered in some way; most likely changes to the semi- crystalline layers judging by the changes seen in the extinction cross under cross polarised light (see Fig 7 and Fig 8). Decay does occur, and starch are clearly removed from the environment - probably in very large numbers, but organic residues themselves help preserve starch - which is itself an extremely stable compound. Everything we could find at the time that discussed likely mechanisms of preservation and degradation of starch was published in the Taphonomy chapter in Ancient Starch Research (Barton and Matthews 2006). Old starch also stains with IKI and Trypan Blue as per our expectations for modern starch - which is also telling us something about the chemical and structural properties of preserved starch. Barton, H., Torrence, R., Fullagar, R. 1998. Clues to Stone Tool Function Re-examined: Comparing Starch Grain Frequencies on Used and Unused Obsidian Artefacts. Journal of Archaeological Science 25: 1231-1238 In this early study (largely in response to the criticisms of residue analysis justifiably raised by Roger Grace) I undertook a study with Richard Fullagar that involved a blind test comparing starch granule counts with assessments of use based on usewear analysis. After I had undertaken a whole tool extraction and counted the starch recovered, the sonic cleaned artefacts were given to Fullagar without any knowledge of my counts and the results compared. That study found a strong correlation between high starch counts (an order of magnitude higher) than either unused flakes or the soils fromt the bag that contained the artefacts. That helped satisfy me that the starch residues were a) a real phenomena related to tool use (unless starch granules know which tools were used in the past and migrate towards them) and b) that cross-contamination from sediments does occur but will reflect the general counts of starch encountered in soils. This of course raises further issues of depostional context and the definition of 'contamination' (which becomes a scale question). For example starch found on tools and in soils may relate to the history of site use, ie, that plants were processed here, contributing starch and tools into the archaeological record. For a more recent blind test on starch granule identification see: Mercader, J., et al. (2007) 4,300 year old chimpanzee sites and the origins of percussive stone technology. PNAS 104: 3043-3048. The starch identification test was undertaken by two analysts (Huw Barton and Robert Tyler) working independently, in fact the results were never disucussed by either party, so it gives a pretty good sense of what can be done and of the reliablity of single granule identifications to species or genus level (at least with this sample of nuts and yams) In press currently I am publishing the results of small two-year study of starch preservation on tools (some left on the surface and some buried). It is a study I set up many years ago before I thought I would get into starch analysis in a major way, so many variables are not recorded such as soil Ph, etc. however, I found that starch (sweet potato) was preserved for two years on tools left on the surface and buried. this study will surface in a special volume being prepared in honour of Tom Loy. I also noted that many starch granules were completely surrounded by very small particulate matter, which I believe (and see arguments in the Taphonomy chapter in Ancient Starch Research, pp. 84-85 on particulate organic matter) can effectively shield starch from microbial attack - if the microbes cannot reach the granule, it cannot be degraded, at least not by that mechanism. I also think that once starch gets into a soil - of which there will be a great quantity - it will be under most threat of decay in the upper humic horizon, what escapes (and again see papers on the properties of Particulate Organic Matter in soils) is essentially locked up in the sediment, and variables such as depth of burial and pore size of sediments will also be important - compaction can be such that bacteria can no longer move. The presence of water is also extremely important - as this is the vehicle for moving bacteria in soil. Further good studies looking at starch in sediments are: Balme, J and Beck, W. 2002. Starch and charocoal: useful measures of activity areas in archaeological rockshelters. Journal of Archaeological Science 29: 157-66. Atchison, J. and Fullagar, R. 1998. Starch residues on pounding implements from Jimnium rock-shelter. In Fullagar, R. ed. A Closer Look: recent Australian Studies of Stone tools, pp. 109-126. Sydney University ARchaeological Methods Series 6. Chapter 8 by Robin Torrence, 'Starch in Sediments' in the Ancient Starch Analysis book is also worth a look in the context of this debate and reviews some useful qualitative and quantitative experiements. Recent work of my own has also looked at starch in sediments from a cave site in Borneo e.g. Barton, H. 2005. The Case for Rainforest Foragers: The Starch record at Niah Cave, Sarawak, Asian Perspectives 44(1): 56-72. (discusses the aroid, tuber starch and sago starch in cave sediments - people must have carried plant material into the site, its entrance is well above the forest floor and decaying underground tubers are unlikely to produce quantities of airborne starch -though a flour mill might. Barton, H. and Paz, V. Subterranean Diets in the Tropical Rain Forests of Sarawak, Malaysia, in Denham et al. (eds). Rethinking Agriculture, pp. 50- 77. this paper further contextualises the results of the starch granule analysis by comparison with charred plant macro-remains from the site. There is every reason to expect starch in 'ancient' sediments is in fact 'ancient' starch. While some people have raised the issue of possible post-depositional transport of modern starch into old sediments - it must occur to some degree - but such a mechanism must equally apply to all particulate matter of similar size, ie., pollen, phytoliths, and micro charcaol etc. It cannot all be contamination - or a lot of pollen analysts are going to be very unhappy people. As for dating, that would be great experiment to do, but I am not sure whether AMS could handle the one or even ten starch granules recovered from most sediment extractions - dating a tool residue with starch might be more likely to give a good result, even so, the quantites of organic matter are very small. I can also help out with starch mimics, if anyone wants to send me pics. Also I had thought of setting up a web site with a lot of that material, but wasn't sure there would be much interest-though this thread suggests otherwise.