Making Seal Impressions

Over the last few weeks we've been making impressions of seals. At Kaman-Kalehöyük, the types of seals that are usually excavated are flat, disc-shaped impressions with a raised or incised design on clay, stone, or metal. In antiquity, these would have been found on containers or communications to demonstrate that they had not been tampered with before they had reached their destinations.

To make these seal impressions, we've been using Sculpey, which is a brand of polymer clay made by Polyform Products in the United States. It can be easily molded and put into a conventional oven to harden. This will allow us to better understand the surface detail, especially of the seals.

First, we worked the Sculpey until it sufficiently softened. Then, we roll the Sculpey into a ball. We usually do a minimum of two impressions of each. This allows us to get the best possible result from the impression.

Conservation intern Davina is working the Sculpey in preparation of molding.

The balls are then flattened slightly and pressed against the surface from which we want to take the impression. The Sculpey is then peeled away from the surface gently.

We then line the baking tray with aluminium foil and place the Sculpey impressions on the foil. The Sculpey goes into the oven at 135°C for 15 minutes, as per the instructions on the packet.

 

When we are done taking impressions of the object, we clean the residue off the surface using some acetone.

Collaborating with Osteoarchaeologists

A cluster of small finds was excavated recently, including some bronze fragments and a green bone. In order to further investigate the possible relationship between these objects, Kaman Kalehöyük conservators sought the expertise of Cheryl Anderson, a PhD student in anthropology at the University of Nevada Las Vegas. Cheryl began by explaining how human bones differ from other mammals and concluded that the bone was a rib of a medium size mammal like a goat or a dog. 

Buried bone often takes on the color of the surrounding soil; conservators are able to elaborate on the scientific aspects of this particular phenomenon. The green color of many excavated metals can be attributed to copper corrosion products (such as copper carbonates, copper hydroxides, copper sulfates, etc.), which form on the surface as copper alloys deteriorate.  Many of these minerals are excellent colorants and certain compounds, like malachite (Cu₂CO₃(OH)₂), have been used as green pigments in paints from ancient times. Because it was buried near these bronze fragments, the bone was stained by the green corrosion products as the copper alloys deteriorated.

Obsidian at Kaman-Kalehöyük

Obsidian is natural glass that forms when volcanic lava with high silica content cools rapidly. Although it only occurs at specific sites, obsidian was valued by ancient civilizations for its various properties – translucency, sharpness, workability. The obsidian from each volcanic site exhibits a unique assemblage of trace elements, which allows scientists and archaeologists to pinpoint the original source of excavated obsidian through instrumental analysis. Determining where materials originate from helps researchers understand ancient trade routes. Most of the obsidian analyzed from Kaman-Kalehöyük comes from Nenezi Dag, Tulce, and Komurcu sites in Central Anatolia, modern-day Turkey. See http://www.busitu.numazu-ct.ac.jp/mochizuki/english/stattk.htm

Conserving obsidian is much like conserving other archaeological glass. The surface is cleaned with ethanol or a solution of water and ethanol. While treating obsidian conservators must be careful of the sharp and delicate edges because obsidian fractures under mechanical pressure with the characteristic conchoidal pattern typical of pure silicates. 

Cleaning a lead object

Last week, a lead figurine was found and brought into the conservation lab here at Kaman-Kalehöyük to be treated. Since it had been freshly excavated, it was still covered with soil. Additionally, it had been bent and twisted at the arms and the waist, causing the figure to look as though it were reclining. Therefore, the primary goals of treatment were to clean and flatten the object.

Davina, the conservation intern, has been working to clean the figure. So far, a number of decorative details have been revealed, especially in the neck area, and areas of carved relief have become more prominent.

Most of the work has been done under an Olympus SZH10 stereomicroscope, but the conservation lab has been able to borrow a Dino-Lite Pro digital microscope from the archaeobotanist on site. This technology allows us to photograph and take video of magnified areas during treatment. Since a good deal of conservation work normally takes place under a microscope, we realized that this would be a good opportunity to show the detailed work being carried out in the conservation lab on this wonderful artifact!

This is a detail of a decorative protrusion on its left shoulder being cleaned using a bamboo skewer under the digital microscope at 30x magnification. Here, you can see how the loose dirt is being removed from the surface and gently blown away using a small air blower cleaner (similar to those used to clean camera lenses), revealing a more shaped element as well as a cleaner surface.

The next phase will be to gently flatten the figure. We are currently looking at several methods for this, including the application of a low heat in conjunction with mechanical means, and will be testing these methods on surrogate lead objects before carrying out the procedure on the goddess figure!

Field Conservation at Kaman

The conservators at the JIAA play many roles, performing in-lab treatments on metal objects, monitoring the environment of artifact storage units, and carrying out technical research relating to excavations and finds at Kaman-Kalehöyük. Conservators are also called out to the field to assist archaeologists with the excavation, stabilization and lifting of fragile artifacts and materials. Last week Lucy Skinner, Melissa Mariano, Elçin Bas, Corinna Koch Dandolo and Carrie Roberts took part in a day of field conservation, during which we lifted a large ceramic vessel and fragile charred wood, among other materials.

The artifacts took up most of the floor space inside of a narrow pit, so we took time to consider in what order the items should be lifted. Lucy started by placing aluminum foil over a piece of charred branch, followed by strips of plaster bandages. While this dried Melissa, Corinna and Carrie excavated around the large ceramic vessel so that medical bandages could be wrapped around it. The bandages provided extra support to the object as it was lifted, as did the compacted soil that was left inside the vessel. The ceramic was placed in a padded tray and tied down so it could be transported to the lab. Inside we found pottery sherds, animal bones, and charred plant material, along with the soil.

Corinna and I were given the task of lifting the charred wood branch. This proved difficult since there was so little space around the object to insert a rigid support underneath it. We figured out that cutting the rims off polyethylene box lids could create supports with just the right amount of flexibility to work the material under the artifact. Once this was done we slowly turned the artifact over onto its back, and lifted it into a waiting box. It was a successful day in the field and a great learning experience for the conservation interns.

JIAA Museology Seminar

The Japanese Institute of Anatolian Archaeology is providing an innovative workshop for local museum curators in different aspects of museum administration. The workshop included seminars on exhibit design, photography, and more, and included a two-day course designed to introduce the students to basic concepts and practices of museum and field conservation. Alice, Lucy, and Melissa developed a series of lectures that opened up discussions on what conservation is, what conservators do, and the methodologies that drive conservation practice. The goal was to offer an introduction to the field, suggestions on what museum curators can safely do to protect their collections, and to stress the importance of consulting with conservators in certain situations.

Alice began day one with a presentation on conservation principles, outlining the ethical guidelines that conservators (and archaeological conservators) work by, and offering a series of conservation treatment case studies. Next, Lucy gave a presentation on field conservation, defining the role of the archaeological conservator in the field and explaining how fragile artifacts can be stabilized and lifted. Melissa gave a presentation on preventive conservation, stressing the importance of environmental control, pest management, and safe housing in the protection of museum collections. The conservators ended the day with a hands-on session on safe handling, and showed the curators how to make storage mounts / packaging for their objects.

Lucy started off day two with a detailed account of art and artifact materials, modes of deterioration, and approaches to conservation in response to deterioration. She discussed organic and inorganic materials, offered examples of treatments, and then opened the floor to Corinna and Carrie to share their own conservation treatment case study. Next, the curators were brought to the conservation laboratory, where they were invited to examine objects through the microscope and carry out simple mechanical of practice metal artifacts. The students - some of whom hadn't used a microscope before - particularly enjoyed this segment of the course. Finally, ceramics restorer Elçin Bas showed the students how plaster fills are done on ceramics.

JIAA Director Dr. Sachihiro Omura hopes to continue this workshop next summer, and based on the success of this week we imagine this might become an annual event at the Museum of Archaeology, Kaman-Kalehöyük

Pseudomorphs

The conservation team often has to carefully examine metal artifacts for pseudomorphs before cleaning.

Pseudomorphs are casts of organic materials in the metal corrosion products and can provide insight on types of materials that may not be preserved otherwise. They form when organic materials are buried in contact with a metal surface. Both positive casts and negative casts can be found, depending on whether the metal cations penetrated and replaced the organic material or if the corrosion products were deposited on the surface leaving an imprint of its structure.1

This is an example of the preservation of a piece of wood on the surface of an iron object.

Textiles can also be preserved. This image shows the remains of a textile preserved on a copper alloy ring. The twists of the threads of the textile can still be seen.


This pseudomorph of wood found on a copper alloy knife shows how much detailed information of the structure of the organic material can be preserved.

1. Carroll, Scott A. 1997. New Thoughts on the Preservation of Bronzes. Anatolian Archaeological Studies VI (6):301-307.

Scott, DA. 2002. Copper and Bronze in Art: Corrosion, Colorants, Conservation. Los Angeles: Getty Conservation Institute.