The Chemical-Visual Divide in Bead Archaeology

Last week I wrote a post about issues with bead reporting.  One of the steps I suggested for improving our current system was for bead specialists to stop dividing themselves into those who look at chemical analysis and those who look at essentially everything else (what I’m calling visual characteristics).  Since very few people reading this post are familiar with the issue, I figured I would explain it in a bit more detail.

There are two primary ways of looking at beads in a scientific manner: chemical analysis or analysis of visual characteristics.  Chemical analysis looks at the chemistry of the bead and often attempts to figure out where the object was made or the recipe used to create the material (if it’s something like metal, glass, or ceramic). The emphasis here is largely on trade routes and the technology of creating the beads.

Analysis of visual characteristics looks at colour, shape, manufacture style, design, size, context, and anything else that is (you guessed it) visual.  This sort of analysis tends to be a bit more subjective.  With chemical analysis, lead will always be lead.  When looking at colour, though, I might say something is green which you would call blue or vice versa.  This approach focuses far more on the use of the beads, the potential fashions associated with them, and what role beads played in society (which may or may not concern commerce).

Neither one of these approaches is better than the other.

Excluding one approach in favour of the other, however, will be detrimental to any research project.

Yet, this is exactly what many archaeologists do – favour one approach over the other.  If a researcher only discusses visual characteristics, that is slightly more forgivable (in my opinion) only if the reason for doing so was a lack of funding or permissions for chemical research.  Chemical analysis is expensive, and it is very difficult to analyse certain materials in a non-destructive way.  Excluding chemical analysis for these reasons, then, is not really the fault of the researcher and makes the omission entirely understandable.  But if a researcher has permission and funding for chemical research and chooses not to do so, then they are willingly and knowingly excluding potentially valuable data from their study.

The much more troubling scenario, in my opinion, is conducting chemical analysis without really looking at the visual characteristics of the beads.  In that sense, the researcher has the funds and permissions for chemical analysis, which means they ought to have the same for looking at visual characteristics (it only takes roughly 5 minutes per bead, and that’s only if you’re taking photos).  I honestly don’t understand why you would be driven to look at chemical analysis and spend all the time and energy doing so only to ignore any visual analysis that could be done at the same time.

I think this divide stems largely from the fact that there aren’t many bead specialists to begin with, and those who work on the chemical side of things tend to be specialists in chemistry, not necessarily an object type.  Those conducting chemical analysis may not feel comfortable discussing visual characteristics, and the reverse may well also be true.  I do know a number of archaeologists who cringe every time the word “chemistry” is uttered, and it baffles my mind.

But whatever the reason for this divide, excluding one approach in favour of the other is going to eliminate valuable data from your study.

Here’s a good illustration from when I posted about Social Network Analysis:

This first chart draws connections between sites based on similarities in the chemical composition of glass beads found there.

Each square represents a site, while each line connects sites with 31% or higher similarity in glass chemistry.

Each square represents a site, while each line connects sites with 31% or higher similarity in glass chemistry.

The second chart draws connections between the same sites, but now uses the proportion of colour as the measure of similarity.

Each square represents a site, while each line connects sites with 46% or higher similarity in glass colour prevalence.

Each square represents a site, while each line connects sites with 46% or higher similarity in glass colour prevalence.

Both charts are vastly different from one another, and neither one provides the whole picture.  Only by combining approaches can we get a clearer sense of the networks at play:

Similarities between Metal Age Southeast Asian sites in terms of glass chemistry AND color - threshold at 55% similarity

Similarities between Metal Age Southeast Asian sites in terms of glass chemistry AND color – threshold at 55% similarity. red is chemistry, blue is colour, pink is both.

If we want to really understand beads (or any other object type, for that matter), then we need to use as many different approaches as we can.  If our goal is to understand a specific object category, then we need to combine methods and become fluent in those types of analysis that are crucial to such an understanding. Rather than separating out chemical analysis from essentially all other forms of analysis, we need to combine these methods in order to get a clearer picture.  Otherwise, we are willingly blinding ourselves to something that could well be staring us in the face.

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About Heather Christie

Heather is an archaeologist, photographer, and writer whose research focuses on beads and bead trade, particularly in a maritime sense. She's currently working working on a PhD in Digital Design (focusing on heritage visualisation) at the Glasgow School of Art.
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