Monday, July 29, 2013

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. 



Friday, July 19, 2013

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.

video

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!