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  • Writer's pictureMatilda Siebrecht

Microscopes and Magnifications

(Can you tell that I'm a sucker for a good alliteration?)

I thought that it was time to introduce a topic that first captured my interest during my masters, and has now become one of my central specialisms; microwear analysis. But what exactly is microwear analysis? What do you need to do it? How do you do it? What is the point of it? The answers are too numerous to present in a single blog post, and so I will be sharing my experience in a series of blog posts looking at this topic in microscopic detail... The first question is possibly the easiest to answer:

What is microwear analysis?

Microwear analysis - when applied to archaeological research - goes by many names; use-wear analysis, traceology, microscopic analysis, to name a few. However, all of these terms refer to the same basic concept, which is that of identifying microscopic traces on the surface of archaeological objects which can provide clues as to how these objects were made and used in the past. Imagine a bronze statue which has been patinated by the years to a pale green, apart from that one spot that has been polished by constant rubs for luck to a bright shine. Or the section of floor with a groove scratched into the wood that is deepened every time the badly-hung door above it opens or closes. Or the dents and rough edges of a child's clay figurine, lacking the smooth finish of a professional touch.

All of these things are traces, created through a specific action or process, and by just looking at the trace itself, you can immediately tell what that process was. That polished nose on a bronze dog statue is clearly the result of regular contact with human fingers. That groove in the floor is clearly created by the door above it. That clay figurine is clearly not finished to the same level as one created by an professional ceramicist. It may seem like a simple concept - perhaps you are reading this and thinking "well yeah of course!" - but the idea that you can identify an action just by seeing the traces created by that action holds so much potential, depending on the kinds of traces that you are able to identify and consequently interpret. The traces observed during microwear analysis are microscopic, and can therefore give detailed clues about so many different kinds of action and processes. And more importantly, the variety of traces that you can observe means that you can see all kinds of different levels of understanding just from a single object.

In this first blog post, I want to introduce the concept of magnification, and how we use different kinds of microscope to look for different kinds of traces. Put simply, we have low-power and high-power microscopy. Low-power - as the name suggests - uses a relatively low level of magnification of up to around 100x more than what we can see with our naked eye. High-power, on the other hand, uses much higher levels of magnification - up to 1000x more than what is visible with the naked eye. That's all very well written down, but what does this difference actually look like? Here is some visual aid:

All of these pictures depict the same object. On the bottom you have the object itself as we would see it with the naked eye, albeit slightly enlarged for ease of visualisation in this particular image. On the left we have a picture taken with a low-power microscope of that same object, and on the right is a picture taken with a high-power microscope.

The important thing to note when looking at all of these images is the scale bar - that little reference to show the measurement of each picture. In the picture at the bottom, we see it at the centimetre level. If you look at the low-power image, you will see in the bottom left corner a little scale bar showing 0.2mm, so significantly more magnified. In the bottom right of the high-power image, you will see 100μm (micrometres), which is 0.1mm, so even more magnified. And as you can see from the pictures, the difference in detail of traces that you can see is huge.

I'll discuss what different traces you can see on different material surfaces in a later post, but for now I wanted to go into a bit more detail on these levels of magnification, and how much you can safely identify trace-wise using low-power and high-power microscopes.

Low-power Microscopy

The most common tool used in low-power microscopy is referred to as a stereomicroscope (although I should mention that, even though this is the term that I was taught in the lab I trained in, the field of microwear analysis is notoriously varied, so it may be that different terminology is used in different labs). A stereomicroscope includes two eye pieces (you may see that stereotypical image of a single eye piece microscope in other areas of research, but for archaeological microwear analysis, we use both eyes), and a light source. If you're lucky, the light source is incorporated into the microscope somehow, but more often, an external source that looks not unlike a book lamp is used.

Also important to note is that for microwear analysis we use reflected light microscopy, where light hits the surface of the object being analysed and reflects back into the lens to enable us to see what we're looking at. Most people think of microscopes as being synonymous with transmitted light microscopy, where the light shines through a sample (usually pressed onto a glass slide) from below.

Another example of a low-power microscope is a USB microscope, which doesn't have eye pieces but can be plugged into the computer so that you can see through the lens via your monitor. The important thing about using USB microscopes for microwear is that they need to be long-distance. A lot of USB microscopes are intended to be used by pressing the lens right up to the object in question (usually a painting or circuit-board or something similarly flat) but this will not work on 3D - often delicate - archaeological objects.

So now that you have your tools, what are you planning to use them for?

Although you can often see the presence of traces of use through low-power microscopy, you generally cannot use this method to further analyse these traces and therefore can only say that it was probably used, but no further conjectures as to how, with what etc. You should therefore be wary of any study who claims to interpret traces of use using only low-power microscopy. What you can see, and often interpret to some level of detail, is how an object was made. But more on that in a future blog post...

High-power Microscopy

If you really want to know not just how an object was made but also how it was used, then you need to bring in the higher levels of magnification associated with what I learnt as metallographic microscopes. It is very rare to find a metallographic microscope that can be used out of the box for microwear analysis, because most of these high-power instruments are designed with transmitted light, rather than reflected light. Some tinkering is therefore often necessary, and for example at the lab I trained in at Leiden University, our lab technician would sometimes have to order different parts of various microscope designs and put them together himself to create something useable for archaeological microwear analysis (thanks Eric!). I cannot afford a proper high-power microscope myself as they are incredibly pricey - unlike low-power options which area considerably more affordable, a proper metallographic microscope will often be flying high with costs in the 10s of 1000s.

It's well worth it though, because you can see so much more with this higher level of magnification. Because of that, it also takes a lot more training to be able to differentiate and identify the different traces, and the process of analysis itself often also takes longer, especially because you need to make sure the object is lying completely flat beneath the lens so that the whole field of view (ie what you can see through the eye piece), unlike the more flexibile positioning possible with lower levels of magnification.

Final words

So hopefully this blog post has whetted your appetite to learn more about the wonderful world of microwear analysis. This is of course just an introduction to the equipment that you need - in the next few posts of the series I will be sharing the research background of this particular methodology, some insights into what kinds of traces you can actually see (and how you can learn to identify them), and some tips and tricks based on my own experience and that of colleagues.

If you'd like to hear more about microwear analysis until I write the next post in this series, you can listen through the button below to an interview that I gave with fellow analyst Dr Éva Halbrucker as part of The EXARC Show podcast series Finally Friday.

Further reading

An article I wrote on microwear analysis for Current World Archaeology Magazine

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