What do floor stains and ancient ales have in common? Well, archaeologists use similar techniques when analyzing residues on ancient surfaces or reconstructing prehistoric beer recipes.
Recently I decided to do some exploratory data analysis using the leftover floor samples I had from the XRF analysis. The idea is to test the floors to see if I can identify some of the biological components of the burnt offerings (e.g. plant species, fish, shellfish, guinea pig–oh, the humanity!).
Enter Fourier Transform Infrared (FTIR) spectrometry. FTIR uses infrared spectroscopy to reveal how compounds adhere to artifacts or surfaces, including organic residues from plants and animals. These signatures can then be compared to known examples in order to identify what types of organic materials were associated with the artifacts or features.
For my exploratory experiment I dissolved 1 cc of a single floor sample in 1 cc each of hexane, amyl acetate, xylene, and de-ionized water. I spun those in a centrifuge so that the homogeneous floor sample settled to the bottom of the test tube. I then piped out the solvent and put it on a depression of aluminum foil. The last step was the most exciting–I waited for the solvent to evaporate. It was literally like watching water dry. The first three solvents dissolved within 30 minutes, but the de-ionized water took much longer.
With the help of Field Museum conservator and science guru, JP Brown (he’s also largely responsible for the CT mummy scanning project), we identified a few particulates in the xylene mixture that may be something. At this point it is too difficult to tell. Unfortunately the amount of residue that remained is probably too small for FTIR but we may be able to use a powerful microscope to identify the material.
We’ve called in another expert who just so happens to be a volunteer at the Field Museum, Dick Bisbing. Dick served The McCrone Group for 25 years as Executive Vice President and Director of Services at McCrone Associates. He specializes in ultra-microanalysis and microscopy for a variety of real-world problems including criminal cases. In other words, he’s like a cross between Bill Nye the Science Guy and CSI.