Friday, 7 March 2014

Blogging Archaeology - future directions

So as noted over on Doug's Archaeology blog, many people who have been taking part in the SAA Blogging Carnival didn't post anything for February, in response to the open ended question of blog about whatever you like. My excuse is, that I did start working on something, but it started to evolve into a full length piece which I will probably submit to either the IA issue or e-book on blogging archaeology that are in preparation. I couldn't help but do a little background reading into the use of social media and blogging as a research tool, and became immersed in the vast amount of literature on the topic. So my theme for February ended up being, Archaeological Blogging as a Tool for Self Reflexivity...or something along those lines. It actually links in very well with a lot of thinking I've been doing recently about bringing together archaeological science and theory, partly due to co-convening a course in theoretical archaeology this year, but also the experience of blogging and taking part in the carnival. As a more discussion based article, rather than dealing with primary data, it is a relatively new area for me, so we'll see how it turns out.

March is the final month of the blogging carnival and the question is, where are you going with blogging or where would you like it to go? I am going to answer this one in terms of my own blog, and again it really follows on from my thoughts above. The reading I have been doing on the use of blogging as a learning tool has really inspired me to make more use of this (and Twitter) in my own research and teaching. I also hope to expand the content of my blog to include more discussions/critiques of recently published papers. Another lesson learned from the carnival is that wider engagement beyond your own work makes for a better blog, and I like the idea of blogs for 'public peer review'. Or simply just commenting on new and exciting work in the world of ancient poo and geoarchaeology!

Saturday, 1 March 2014

Micrograph of the Month: the woods decay and fall

Close-ups of decaying waterlogged wood. Upper left showing 1. latewood with secondary cell wall intact 2. earlywood with loss of secondary cell wall. Upper right showing loss of birefringence in areas subject to decay

Another fab example of the sorts of things that go on in medieval waterlogged deposits. I posted some pictures of this waterlogged wood a couple of months ago, as well as a nice example of the formation of vivianite in the same deposits. Here we have another example of waterlogged wood, but I've added some close-ups in cross polarised light (XPL). For the non geoarchaeologists in the audience, this is a technique in microscopy where you change the type of light you use to look at a sample, by inserting polarisers on the microscope. Polarised light vibrates only in one direction. On the geological microscope, the lower polariser causes the light to vibrate in an E-W direction, whilst the upper polariser/analyser filters light that is not vibrating in the N-S direction.

In non-crystalline specimens such as opal phytoliths and charred wood, this normally means that everything would go black, as no light will pass through. However, when crystalline materials are present, they split the light in such a way that when it reaches the analyser, it causes interference, and passes through instead of being filtered. This splitting of the light  is due to an optical property called birefringence, which means the material has a refractive index that depends on the polarization of light. Minerals tend to be highly birefringent, and can be identified on the basis of colour changes when they are viewed under the XPL. However there are also biological materials which are crystalline, such as cellulose.

In the micrographs you can see here, the images on the left show the wood under plane polarised light, and on the right is the same view in XPL. Initially I thought that this was partial burning of the wood as there are areas which are completely black, however after a bit of research, I think what we may have is  fungal rot in this wood. Because the sample is waterlogged, some of the cellulose has preserved, hence the birefringence (shiny!).  This is a typical pattern, where the cellulose of the secondary cell wall in the earlywood part of the tree ring decays first, followed by the latewood. I suspect a chat with a conservator might be able to help - any waterlogged wood specialists reading?