Analysing the Ambum Stone

The Ambum stone is a rare stone sculpture from Papua New Guinea. Prior to this conservation project there was very little information relating to its cultural background or age because of the lack of cultural continuity between the object’s makers and the present inhabitants of the area it comes from.

During an overseas exhibition the Ambum stone suffered a fall, causing the object to break into three large sections. It sustained some smaller chips and surface bruises.

One of the breaks followed a fault line in the stone – common in sedimentary rocks – which was indicated by old, shallow cracks visible on the surface of the object prior to damage. A small amount of plant material was found in this crack, providing an opportunity for dating the sculpture using radiocarbon dating – a method that provides age-estimates by testing organic material. This material penetrated the crack in the stone at some stage before the object was found in the 1960s, during this time it was either buried underground or left on the surface surrounded by accumulating debris.

The radiocarbon analysis indicated the plant material is approximately 3500 years old, making this the minimum age of the object. This is also the first known scientific result provided for any prehistoric object of this type from Papua New Guinea. On top of the radiocarbon dating, access to the internal, unweathered parts of the stone also provided the potential to analyse the geology of the sculpture – this analysis indicated that the rock was a volcanic sandstone (crystal tuff) with a thin, glassy layer found on the surface of the sculpture. This layer, called ‘desert varnish’, is often found on rock surfaces exposed to the elements for extended periods of time. The Gallery's Conservation team cross-checked these results and found them compatible with the historical information documenting the location and circumstances of the discovery of the Ambum stone in the Ambum Valley of Papua New Guinea.

This project proves the great potential for conservation research, which not only provides information on the object itself, but enhances our understanding of the ancient cultures these objects hail from. Following the analysis a successful conservation treatment was carried out by the Objects Conservation team who were able to restore the stability and integrity of the object, allowing it to return to public display.