Recovery of difficult objects during excavations

In certain special cases the restorers at the Department of Prehistory are asked to travel to excavation sites to carry out the recovery of difficult and particularly valuable objects. This can involve various different techniques. Two of the most common are the ceramic recovery method, developed by the restorers themselves, and the stabilisation method using cyclododecane.


Recovering ceramics

The restorers have developed their own method for recovering heavily fragmented ceramic vessels from the Hallstatt burial site. The vessels in the graves have been crushed, but the fragments from a single object are still lying directly next to each other, so it is important to not disturb the grave and thereby change the position of the fragments in the ground during the recovery process.
The restorers use square wooden boards covered with fleece. As the fragments are removed from the ground one by one, they are arranged on the board as far as possible in the same pattern as they were found in the soil. Pottery fragments are often found in several layers on top of each other in the graves. A separate board is therefore used for each layer. When a board is full, it is covered with moistened cellulose and tightly wrapped with adhesive foil. This prevents the shards from moving and means the boards can be safely transported in a vertical position, thereby saving space.
When they arrive at the restoration workshop the boards are unpacked and photographed. The photo of each board is then printed out on a scale of 1:1 and placed on a different board of the same size and shape. The shards are then cleaned one by one and placed in their original position, which is easily visible thanks to the photo. The broken surfaces are then cleaned. The team at the Department of Prehistory generally uses a sandblasting machine for this process to minimise damage to the sharp edges of the broken pieces.
Once completely cleaned, the ceramic fragments are placed on a third board with a 1:1 true-to-scale photo and can be pieced together like a jigsaw puzzle. This procedure, which takes a little more time on-site than simply collecting up the pieces, reduces the process of putting the fragments back together by roughly three-quarters.

Stabilising metal using cyclododecane

Since 2009 the museum’s restorers have also been using cyclododecane to stabilise fragile objects, especially those made of metal. Cyclododecane is a hydrocarbon compound that can be liquefied by heating it in a water bath. Liquid cyclododecane is then applied to the finds in several layers using a brush. As it cools, it hardens once again and thus forms a stabilising protective layer for transport. Within 14 days the material dissolves and leaves behind no residue, meaning the objects can be restored in the workshop under the best possible conditions.