Friday, August 16, 2013

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.

Monday, August 5, 2013

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.