Hello, and welcome to the Thin End of the Wedge. The podcast where experts from around the world share new and interesting stories about life in the ancient Middle East. My name is Jon. Each episode, I talk to friends and colleagues, and get them to explain their work in a way we can all understand.
This episode, we take our first look at the wonderful world of archaeological conservation. If you’ve ever visited a museum, you’ve seen the results of an enormous amount of work by conservators, although you probably didn’t realise it at the time. From excavation, through museum storage, research, and display, objects are the subject of a lot of patient, painstaking effort.
Conservators rarely get the credit they deserve, because they typically operate out of view, behind the scenes. But these are the people who, on a practical level, ensure that the objects produced by ancient cultures survive for future generations to see and study. Even many researchers specialising in the ancient Middle East have never met the conservators who facilitate their work, and often have only a very limited understanding of what they do, and why they do it that way.
We learn most of what we know about the ancient Middle East through objects. That goes for those of us who specialise in reading the texts as well. We sometimes express ourselves in strange ways. For example, we routinely talk about “cuneiform tablets”. But of course, the tablets aren’t cuneiform (that is “wedge shaped”). It’s the writing that’s cuneiform. We all know that what we really mean to say is “clay tablets made to contain cuneiform text”. Even that’s not quite right either, though. Tablets aren’t made of clay; the material is a much coarser mud. The physical qualities of tablets are important, and we’ll come back to that in future episodes. But for now, it’s worth stressing that these ancient texts take physical form, and one that needs care.
Our guest is a conservator with decades of experience working on excavations and in museums in Europe and the Middle East. And she’s literally written the book about the conservation of clay tablets.
So get yourself a cup of tea, make yourself comfortable. And let’s meet today’s guest.
Hello, and welcome to Thin End of the Wedge. Thank you very much for joining us.
Hello, and thanks for invitation.
Could you tell us please: who are you, and what do you do?
My name is Carmen Gütschow. And I’m a diploma restorer of archaeological objects and specialised in cuneiform tablets.
Could you start by explaining what a conservator does, please?
Yes, my job is carefully cleaning of excavated objects from soil and crust and if necessary, to join broken pieces or to consolidate weak objects. And this work can be on excavations or in collections or for exhibitions.
What kind of work does that involve?
The different materials need different ways of cleaning and treatment. So you have to examine your objects, if they are sensitive or solid to decide the right treatment for cleaning like dry or wet, or maybe with chemicals. And to choice the tools for cleaning like wooden stick or scalpel, brushes, or using fine machines like an ultrasonic or a hand grinder for example. And also the kinds of glue and which concentration for consolidation or bonding is needed. Also, the right packing and storing in the end of the work is part of the job, or perhaps the preparing for exhibitions.
Can you give us some examples of what you mean? What would make you choose one treatment method or type of tool rather than another?
For example, the cleaning of pottery: proper fired pottery, you can wash. But if the pottery is low fired or heavy affected in the ground, the material can be soft and so to bath or to brush the surface can damaging the object. In that case, you must choice a dry cleaning with brushes and tools to remove the soil or slightly damp by rolling over the surface with cotton swabs. If the pottery is painted, this layer can be sensitive and washed away. I’ve worked on soft painted pottery and the painting seems relatively solid when dry but turns super soft in wet condition. Then you could easy whip off the painting just by touching with your finger or a soft brush. Sometimes I asked myself how many pottery known as unpainted was maybe painted before the general brush washing on excavation. Therefore, my advice is to keep an eye on the sherds before drop into the water basin and use middle soft natural brushes. They’re not these hard plastic ones which I often noticed. I’ve worked out some ways to clean those sensitive painted surfaces wet and with chemical treatments to soften sinter crust on top.
What is sinter?
Sinter forms over a period of time on surfaces and is a certain leaching minerals like calcium carbonate. Ceramic is often covered by sinter crust, but also stone and metal objects. Those calcareous crusts can be softened and removed by acids like citric acid or acetic acid. The artefacts can be bathed in low concentration or you can make a compress. Important is to neutralise the acid by washing or compresses in the end. Otherwise, you risk that the remains of the acid were damaging the artefacts after a while. It’s fiddly and time consuming, but it’s worth it.
Once the pottery fragments–or “sherds”, as they’re called–are cleaned, sometimes it’s possible to join them back together into a more or less complete part isn’t it? And that’s also one of your jobs.
To join the pottery is a bit like a 3D puzzle. The most people thinking the bonding is easy. But if you have seen some objects joined by a lay person, you will see it’s not that. And it’s time consuming to rework that. To make a proper bond, you have to follow some rules of bonding. For example, a weak breakage will need a consolidation before and a more rough sherd need thicker glue than a finer one. If you don’t have a full contact area, you will need a filler in your glue. And don’t smear the surplus over the surface; remove it directly. Also if you have bubbles or run marks, for example.
What about other materials then? Ceramics are relatively robust compared to some other objects.
Organic materials need a carefully treatment too much which could destroy by swelling the material. On the other hand drying out after exposing could produce cracks and deforming of the objects. These groups of material will need a certain humidity and needs to keep away from sunlight and controlled to prevent moulding.
How do you control humidity?
To control the right humidity on site is not easy. And you didn’t have climate control systems like in a proper lab or a storage. And sometimes you have to be a bit creative. So to keep the environment of an excavated condition, it will be good to put those objects with some of the soil in a box and covered breathable, or in a bag till you will have the possibility for their conservation treatment. important is to control wet or damp objects to prevent moulding processes. And the best is to keep them cool as possible.
What about metal objects? We might imagine that they’re strong, but they can be vulnerable can’t they?
Metal objects are a bit different up to the metal and the alloys. Iron, for example, is often in very bad condition, because it’s very fast affected by wet conditions and salinity of the soil where it’s buried in. Iron often shows the swollen or cracked body. Normally it would be good to desalinate them, but on site you don’t have the time and opportunities for that. So they need to be dried and stored in a dry condition to prevent ongoing processes of corrosion. Copper and his alloys have sometimes produced a patina layer which works like a natural protection on the surface. The corrosion on the crust will just reduce up to this patina and never to the shining metal if preserved. Sometimes the artefacts are completely corroded through, but the patina if protected will showing only the details of the original face.
So how would you treat a metal object suffering from corrosion?
For reducing the corrosion, you have different options up to the hardness and the thickness of the crust. The softest tool is the wooden stick, but normally you will need a scalpel. And for a stronger crust you can use ultrasonic like the dentist use to remove the calculus. But also fine hand grinder tools or sand blaster can be helpful. And sometimes you will need a chemical treatment to soften the crust. Gold, silver and lead, for example are softer metals and they need a careful treatment to avoid scratches. It’s often precision work under magnifying glasses and you will need some patience. And after removing the corrosion, the metal needs to be protected. Therefore, a thin varnish, for example, by Polyvinylbutyral 30 or a microcrystalline wax like Cosmoloid H 80 can be applied.
Do you stick metal objects together in the same way as pottery?
To bond metal, a stronger glue is mostly needed. For example, an epoxy resin like Araldite 2020. But it’s not easy to handle, because it will take 24 hours to harden and it’s unsoluble after hard. You need to fix the bond very good against moving or Polyvinylbutyral 30 can be used for lighter bonds.
How do you decide what treatments to give on an archaeological site when the range of options available is smaller than it is in a laboratory?
Material and the condition of the object is to choice the right treatment, but also your opportunities. If you work on a site, your treatment is normally limited as working in a well prepared lab. And also the time you have is a factor. If you work on site, you have limited time. And so you have to decide “Can I do just to limit to basic treatment? Or can I do more expensive treatment like replenishment on a vessel and a retouching? Or can I finish the treatment till the end of the campaign or must be decided a limited treatment to protect the objects until the next opportunity with more time? Or till I can organise the equipment and material for special treatment?” When I work on site, I choice a basic equipment of glues, chemicals, and tools, which are able to conserve the most and general incidental of objects. For example, the glue, Polyvinylbutyral 30 can be used for the most materials for consolidation and for bonds.
The most important solvents are acetone, ethanol, and distilled water for dissolving the glues and cleaning the surfaces. And of course, scalpels, brushes, and cotton are always in my bag. Working in a proper lab, of course, will offer you more and better opportunities even for special treatments, like extraction systems by working with chemical vapours or a drying cabin for iron, or a sand blaster and a wider range of chemicals and other stuff for treatments.
Does the site being in the Middle East affect the treatments you choose?
If you work in Middle East, you have also to consider the hot and mostly dry climate, because this will have influence of the properties of the chemicals and glues. The glue which works good in Europe must not be a good glue for Middle East countries in general. But this is a mistake I recognise very often. For example, the very common glue Paraloid B 72 is long time used in conservation and has good properties. And so the most projects brought this glue to the excavations in the Middle East. But why it’s not a good choice for Middle East? This glue has a glass transition point by 40 degrees. That means by this temperature, the glue gets soft. And everybody knows that the temperature in Middle East is long time over the year over 40 or 50 degrees. For those climates, you will need a glue with a higher glass transition point to get sure that your bond will stay strong. The glue with similar properties like Paraloid B 72 is Polyvinylbutyral 30. His glass transition point is 68 degree and I have good experience with this.
In general, I prefer glues in form of a powder or granulate, which will be dissolved on place when needed. So you can bring the glue by airplane and store them for a long time without the risk of drying out. Polyvinylbutyral 30 is a powder and dissolves easy enough in acetone or ethanol. Ethanol is the better choice, because it evaporates slower even in dry and hot climates. Another point is that ethanol can be found everywhere in pharmacy shops. Acetone was sometimes more difficult, especially in Afghanistan, for example. So you have to consider for how long you can store the chemicals and glues. The epoxy resin Araldite 2020, for example, needs to be stored cooler after open. And so you will need a fridge. Otherwise you risk that the glue lose his properties early. And it’s also important to know what’s available in the countries, and what are the rules for transport by plane. Some solvents and liquids are not allowed. For example, a water based glue in your luggage is no problem. But a glue with acetone is forbidden.
You have particular experience in treating cuneiform tablets, don’t you? Could you explain about that? What problems do they present and how do you treat them?
Well, my special field is the conservation of clay tablets since 20 years now. The clay tablets are a special group of objects. I will distinguish between tablets on site and in collections. The problem during an excavation is that the material of the tablets and the soil around is very similar. They are hardly usable and mostly unfired. In a wet condition also the tablet is wet and more sensitive and slightly soft. And if the ground is dry and hard, you will risk to break the tablets or the surface can be brutal and flaky. The most suitable way to expose is with the soil around and to dry them slowly after exposing to prevent cracks. They should be keep away from direct sunlight and stored covered in the shadow. After drying the clay a stronger and the tablet can be carefully cleaned from soil and consolidated if necessary.
A treatment that many people think of in relation to tablets is firing. Could you talk about that please?
Firing for conservation is not necessary if the storing the tablet is dry and stable. But an unstable climate could start processes like the growing of salt crystals, which destroying the tablets. And that’s why the tablets were fired after excavations in the past, sometimes directly on sites or they did it later in the collection. That’s the reason why we found the most tablets in collections as fired tablets today. In the past, just a small amount were fired, like prisms or nails and some documents. Another reason could be a fire in a house. After the first excavations in the past before they start to fire tablets, they recognise that the tablets crumbled into dust after a year. The idea was to fire the clay to make it strong like a pottery material. But they recognised that this fact alone doesn’t brought the result of stabilisation. They figured out that the problem of the destroying was the salt inside the clay structure. By an unstable climate of the storing, the growing of salt crystals will be activated and breaking and crumbling the tablets. Unfired or fired, doesn’t make here a big difference.
After firing the clay turned into a new material with other properties. This new material is ceramic which is waterproof and therefore the tablets can be bathed in distilled water to wash out the salt. This treatment works and so it became the common way of conservation for the tablets. It has taken some decades to modify the procedure, mainly in the point of the schedule. Sometimes the tablets broken while the firing. The reason for that could be that the firing was too high or too fast, and also the reaction of salt by higher temperature. So, for example, calcium carbonate produce a gas pressure over 630 degrees. The transformation process from clay into ceramics starts around 600 degrees. And firing tests at the British Museum around 2000 figured out that the temperature up to 630 degrees makes the most tablets strong enough for the water treatment, and showing a minimum of damaging like cracks or breaks during this process.
The following desalination of tablets can take some weeks or months, but also after that the tablets will always need monitoring. The general firing for conservation is not longer common today. We try to keep the original condition if possible now. In conservation, we are always eager to preserve the original condition best as possible and with less external influence as possible. From that point, I wouldn’t fire a tablet if not necessary to preserve the original of the tablets.
How would firing itself change the condition of a tablet?
The firing of tablets is a massive invasion, because the firing process change the material from clay into ceramic. This material will have new properties which we just need for this desalination process. But also the color will change while the firing, mostly into a reddish terracotta. And if the firing was too high, normally over 800/900 degrees, also the size start to shrink. So we would change a lot of the original by that.
Why are conservators so keen to preserve the original condition of objects? What might we lose by firing a tablet?
What does it mean for the different scientists. So for example, if an archaeologist found an unfired tablet, contains decent information of the in situ situation of his site. He found an unfired tablet in a room or library or a vessel. Or he found a fired tablet, because the place was exposed to a fire in the past; for example, the house was on fire. Or he found a tablet which was conscious fired in the past, like a prism or a nail. So you see the tablet contains more information as the words on it. By firing for conservation, I would change or destroy this information.
In case I need to fire a tablet, I have to document all information about the condition before to keep this information. If I fire an unfired tablet, I change the colour and organic material in the clay will burn out. But also if I refire a tablet, which was exposed to a fire, I will change some information about the event of this fire, like the temperature or the place in the fire. For example, there are some tablets in one place with irregular colours in black and reddish, then you can get an idea of the position of the tablet during the fire. Black means there was no oxygen on this place during the fire, because maybe the tablet or this part of the tablet was covered by soil or another object. And reddish part means that this part was exposed to the fire. But after a controlled firing for conservation, the colour will be just regular reddish.
And now we’re looking from the point of a philologist. His main interests are the cuneiforms which are the same fired or unfired. The text will not change by the firing. Therefore, in particular in the past, they easier decide to fire a tablet to make her stronger. So the history of tablet conservation shows that this becomes long time the common way. The British Museum was here the first address and developing of this procedure. But maybe since 15-20 years, we refrain more and more from that. If there’s no need, and other options like a good climate controlled storage and monitoring, the idea to preserve the original condition dominate today.
You explained about tablets on archaeological sites. What about those in museum collections?
If you have seen some collections, you will recognise that the problems are more or less everywhere the same. It wasn’t common to wrote reports about the treatments in the past. Therefore, often we don’t have information about the treatment like fired or when, how, and desalinated, or what kind of materials for conservation or consolidation for gluing are used. In collections you can find many different conditions from unfired to fired tablet, restored and unrestored tablets, fake joins of different tablets, many kind of glues and other materials for consolidation like wax or resin or filling material like plaster. With some experience, you will have an idea of the most kind of used materials also without the old report. But for sure notes will be helpful and also interesting for the history of the restoration. Today, it is a must to write reports of the conservation from the condition before till the end of the treatment.
One of the main work in collections is to rework the old restorations. Some of the old glues are yellowed or brownish, and sometimes they become brittle and bond gets open. Sometimes bonds are sloppy worked, because they use too much glue or the joints are incorrect, and the cuneiforms are covered by glue or wax consolidation. Also, the filling with plaster or glue mix was often sloppy worked and cover the surface. By chance the old glue can be dissolved with acetone, ethanol or water. But sometimes they become insoluble and need to be reduced mechanical with scalpel. If the condition of the tablet is stable, it’s easy to rework the old restoration. But the tablets are often sensitive or brittle, and you must be very careful. If the tablet was completely broken in small pieces or flakes and just hold by the sloppy restoration, you can’t open and remove all the old glue. Then you can just try to cut off what’s loose by rework the mess.
I’ve worked in many collections like in the Near East Museum in Berlin, the Hilprecht collection in Jena, or the Uruk-Warka collection in Heidelberg, that Böhl collection of the NINO in Leiden and the Iraqi Museum in Baghdad. Then, as today, you can’t find special clues for conservation in Middle East countries. Therefore all the foreign excavations brought glue from Europe or other Western countries. That’s why we can find the same kind of glue all over the world in these collections. Local excavation often used other glues from their local market. They are mostly unsuitable for conservation, but they had no option.
Cuneiform is written on so called “clay tablets”. The tablets are basically mud, and they’re found covered in mud. You’re not a cuneiform specialist. Can you explain how you remove all the mud from a clay tablet, without risk of damaging the surface?
I’m often asked “How can you uncover the cuneiforms if you can’t read them?” My answer is, “I’m reading the material. I know the form and the structure of the wedges”. And in general, you can see the fine difference of the mud material from the tablet and the soil on top under a magnifying glass. It’s normally good visible and bit experience is helpful of course.
What are you working on at the moment?
My current projects are the restoration of the Böhl collection at the NINO in Leiden and the Sippar Library in the Iraqi museum and the museum project in Yazd in Iran. Unfortunately, all projects are laying on ice. The Sippar project is a cooperation between the LMU in Munich by Professor Dr. Enrique Jiménez and the University of Baghdad by Dr. Anmar Abdul Fadhil, and the Iraqi Museum in Baghdad. By our last day in Baghdad, we will also start to think about to organise a kind of conservation preaching for our tablet at the museum. Everything was on a good way and we are all looking forward to continue that project.
How can we follow your work?
About the conservation and restoration of tablets, there’s my thesis published by the BBVO–Berliner Beitrage zum vorderen Orient–volume 22nd. It’s just in German. And the title is “Methoden zur Restaurierung von ungebrannten und gebrannten Keilschrifttafeln: Gestern und Heute”.
A note for listeners: in English that’s “methods of restoration of unfired and fired cuneiform tablets: yesterday and today”
And some of the projects like the LMU Baghdad project and the NINO also mentioned my work on their home pages.
Thank you very much.
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