Preparing wood samples: when you´re on the woodway trying to find a unique preparation method
Dr Susanne Lindauer1, Dr Johannes Tintner-Olifiers2, Dr. Niels Bleicher3, Dr. Hannes Knapp1, Dr. Ronny Friedrich1, Prof. Dr. Roland Schwab1
1Curt-engelhorn-centre Archaeometry, Mannheim, Germany, 2Natural Resources and Life Sciences Vienna, Vienna, Austria, 3Competence Centre for Underwater Archaeology and Dendrochronology, Zurich, Switzerland
Usually, when preparing wood samples of either species, cellulose, especially alpha-cellulose, as the outcome is thought to be the most reliable part of the sample for radiocarbon dating. We noticed that some samples used as blank samples in our laboratory do not work well after cellulose pretreatment – if they still contain cellulose at all – and rather end up with a finite age instead of being radiocarbon dead. Hence we started a test comprising of different wood blank samples as well as some younger species to get an idea about systematic shifts due to pretreatment method chosen.
Here, we present outcomes of a range of different pretreatments from rather harsh alpha-cellulose and very soft pretreatment with diluted acids and base steps. The most problematic wood to date, however, is waterlogged wood. Therefore, we included some of these kind of samples in our test as well. All younger wood samples were cross-dated via dendrochronology prior to radiocarbon dating.
To understand the sometimes surprising outcomes we checked the samples with a microscope and in more detail with a Scanning Electron Microscope (SEM) as well as Fourier-Transform Infrared Spectroscopy (FT-IR) hoping to understand the samples better.
In conclusion it can be said that to use a sample as process blank in the lab the range of useful sample preparation steps for this sample needs to be determined first. As the data shows it is of no use to prepare a sample for cellulose extraction if the cellulose is badly preserved and then leads to erroneous ages.
Dr. Lindauer is responsible for the C14 sample preparation laboratory and for the luminescence laboratory at CEZA since 2010 when the lab started working. Apart from her many scientific interests such as interdisciplinary research on marine questions in context of archaeology and paleoclimate, she is interested in laboratory methods and here uses her second profession of having learned to be a technician as well. She enjoys being able to work directly with the samples and test their limits but is always curious to understand the contexts.