Conservation and restoration of metal

Most of the metal objects currently being worked on in the NHM restoration workshop come from the Celtic settlement at Roseldorf. They range from weapons and wagon parts to tools made of iron. There is also a considerable number of the iron objects originating from the latest excavations at the Hallstatt burial site. Swords and lance tips, daggers and knives were placed in the graves of wealthy people in prehistoric times to smooth the deceased's journey into the afterlife.

Grave goods from this burial site include many bronze objects. In addition to rings, fibulae and pins, which belonged to the costume of the deceased, recent investigations have also repeatedly brought to light exceptionally beautiful bronze vessels. Gold objects have also been found at the Hallstatt burial site.
While these only require cleaning, the iron objects in particular often pose a challenge to the restorers. Unlike with bronze items, the corrosion of iron objects is often so far advanced that there is nothing left of the actual metal.
Sometimes all that remains is the material left behind by the corrosion process, which traces the shape of the former object. This is almost impossible to see with the naked eye, so many finds are x-rayed before the restoration process begins.
Only once an X-ray has been carried out is the surface carefully exposed using sandblasting machines, diamond cutters, scalpels or similar tools. The result is then documented in text and pictures before the restoration begins in earnest. Iron finds are usually stabilised with microcrystalline wax, while a paraloid protective coating is generally applied to bronze.



In addition to the new finds from the department's research excavations, the restorers also have to rework old finds again and again, because the corrosion process restarts after centuries or decades. This is not necessarily due to inferior conservation techniques of the past. Even the most modern conservation methods cannot completely stop the decay of the objects but instead only slow it down significantly.

Re-restoring old objects is often a very interesting task. It gives the museum’s restorers an insight into the experimental techniques used by their predecessors, who laid the foundations for today's modern conservation methods. At the same time it is not unusual for previously unknown details to suddenly become visible thanks to the new possibilities offered by modern techniques.