Tuesday, October 28, 2014

False Colors

Over the years, I have obtained copies of all of the NESAT issues.  Only a few of them are photocopies of dubious pedigree (though I have always sought to obtain copies of the NESAT books on the open market, and have only resorted to photocopies, for research purposes, when market copies have proved unavailable).

NESAT XI, the latest volume, is striking for the dramatic increase in articles that are based expressly on scientific experiment and unusual research techniques.  Consider the following:
  • Solazzo, Caroline; Peacock, Elizabeth; Clerens, Stefan; Dyer, Jolon M.; Plowman, Jeffrey E.  Potential of Proteomics for the Analysis of Animal Fibres in Archaeological Textiles. (pp. 139-144) Discusses analysis of protein complexes in archaeological animal fibers (which is called a "proteome") to deduce the origin of such fibers.

  • Wiesner, Ingrid; Stelzner, Jörg; Ebinger-Rist, Nicole.  Virtual Analyses of Neolithic Textiles (pp. 109-118).  Discusses use of computer modeling of neolithic fibers to "see" areas of the fibers that cannot be seen without destroying or damaging the find, in order to make deductions about the find (such as the fiber manipulation techniques used to create it).

  • Llerg, Yolanda; Riera, Santiago; Servera, Gabriel; Miras, Yannick; Eusebi Garcia-Biosca, Joan; Miguel, Marina; Picornell, Llorenç; Cabanis, Manon.  The Application of Pollen Analyses in the Study of Burials and Related Textiles:  The Studied Cases of King Peter The Great's Medieval Grave and the Prehistoric Funerary Cave of Cavades Pas (Spain) (pp. 119-123). Discusses analysis of pollen found in and on archaeological textiles for use in ascertaining information about burial practices.
I am pleased to see that scientific progress is continuing to enable archaeologists to obtain more and more information from very small or very damaged textile and other grave finds.  But it strikes me that it can be even more useful to have information that warns us that our tests may not be telling us the entire story.  Such information has been supplied by an experiment performed by M. Ringgaard of the University of Denmark, called "Migration of Dyes in Wet-Site Archaeological Textiles."  Copies of the NESAT posters, which describe the experiment briefly in both English and German, may be found on line here.

Ringgaard devised a simple text, which began with dyeing swatches of wool and silk with different, specific, natural dyes--indigo, cochineal, madder, weld, oak galls, and walnut--and keeping records of which dye or dyes was used on each.  Some of the swatches were dyed using mordants, and records of which swatches used which mordants were kept also.  Some of the samples had white, undyed wool swatches fastened to them. All of the samples were then buried in boxes filled with waterlogged peat and the boxes were stored in a greenhouse at a stable temperature and humidity level.  At different times ranging from 8 months to 4 years after burial, some of the samples were removed, freeze-dried, and subjected to photo diode array analysis for dye substances. 

M. Ringgaard found that both dyes and mordants leached from the fabric samples.  In the case of the samples buried with white wool samples attached, the leaching process often clearly visible, but the fabric that had been leached into in this way tested positive for dye.  More interestingly, dye from some of the dyed fabrics was detected in fabric swatches that had been dyed with a different dye than the one detected by analysis, suggesting that migrating dyes do not always (or only) migrate to the nearest textile.  M. Ringgaard observed:
Although no significant trace of indigo was found in the “migration patch,” indigo was found in two swatches – weld (reseda luteola) - dyed – that had been placed next to an indigo-dyed textile during the burial. If it had not been known the textile was dyed with weld only, the interpretation of this analysis would have been that the textiles originally were dyed green.
M. Ringgard concludes, "If more than one dye is traced in an archaeological textile, one has to consider if this is an intended mixture of dyes or if it could be due to migration from other sources."

In my opinion, the implications of these results are twofold.  First, the fact that a textile tests negative for the presence of a dye substance may not mean it was not originally dyed.  Significant migration of dyestuffs took place in M. Ringgaard's experiment over a course of months or years.  Many archaeological textiles have been buried for centuries, and any dye substance in them may long since have leached away, forever lost to researchers.

The second possibility is just as troublesome.  Over years, or centuries, a dye substance might leach away from a textile, not into the ground, but into a different textile, giving the impression that the second textile had been dyed even if it had not been, or that it had been dyed with different substances than those that were actually used to dye it, resulting in the possibility of a faux "green" type of result.  

M. Ringgaard proposes that dye testing should be performed on multiple samples taken from different parts of the same textile, to see whether the results vary dramatically in terms of what dyes are detected and, hopefully, ascertain whether migration of dye or mordant has affected the test results.  This may turn out to be a successful corrective measure, but the study is a useful reminder that neither a positive nor a negative result for the presence of a dye can be entirely trusted.  The Ringgaard experiment has shown that dye substances can migrate away from fabric buried in wet ground and raises the possibility that prior testing results have, in effect, clothed some textile specimens in false colors.  Anyone researching the history of early costume needs to keep that possibility in mind.


  1. Alas, but "my current account " does not have access to view this page." Any idea what I have to do to be able to see those posters? I really want to see this one!

  2. Poster link on the left ..... http://www.nesat.de/esslingen_xi/dank_en.html

  3. Actually, "proteome" means the entire set of proteins expressed by a given cell/tissue/organism at a given timepoint, rather than describing protein complexes.

    That dye analysis is fascinating. It's great to see archaeology embracing science.

    1. I stand corrected; I was writing this post very quickly, in between a bunch of things I was trying to do this week.

      As I was trying to say in my essay, this particular issue of NESAT is thick with papers about studies that marry scientific techniques to archaeological deduction. I agree with you; it's a wonderful development.