Chemistry and Sourcing

Chemical analysis of glass beads has become quite popular in recent decades, and can help quite a bit with understanding the origins of the beads.  But in general, we archaeologists tend to make the same assumption: that the technology for one recipe of glass must have originated in one single place.

But why do we have to assume that silica-soda-lime glass technology originated in a single location?  Why couldn’t multiple groups independently come up with that way of making glass?  We might think that it’s difficult for different groups to come up with such similar glass technologies on their own, but there has been work done to suggest the possibility.

In pre-Roman times, the groups in modern day Egypt and the Middle East made glass using a potash source for soda, resulting in a glass type we call v-Na-Ca (v for vegetal or plant-based source of Na, or sodium, and Ca for calcium (derived from lime)).  When the Romans rose to power and dominated the region, they developed a new glass recipe that used a mineral source of soda rather than a plant-based one.  We call this type m-Na-Ca (the ‘m’ denoting the mineral source of soda).  So far, all this is in accordance with the assumptions made that recipes originate in a single region.

Once the Romans fall out of power several centuries later, the areas in modern day Egypt and the Middle East eventually move back to making v-Na-Ca glass.  This was probably due to the availability of material, given the destruction of the Roman trade infrastructure.  But the evidence from the Middle East suggests that this was not simply remembering the original recipe from several centuries earlier; the glass-makers were experimenting with new glass recipes given the materials they had and actually ended up with a type of v-Na-Ca glass that was significantly different from the one made in the region several centuries before.

Yes, the Middle East had already been working with glass technology for a very long time, so this experimentation was not the same as a group never having made or worked glass coming up with a way to do it.  But it is still the same general type of glass as was being made in the region originally, still v-Na-Ca.  So can we really make that assumption that general glass types are specific to or originated in certain regions?  Or, perhaps a better question, can we really get away with not clearly addressing that question/assumption in our research?


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.
This entry was posted in Lab Notes and tagged , , , , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s