Ancient rock reliefs in the necropolis of Naqsh-e Rustam are important testimonies of the development of an outstanding monumental art over the centuries, in close relationship with their natural context. The rock reliefs underwent natural and anthropic decay processes in the course of time, which caused dramatic changes affecting their aspect, leading to the loss of fragments and in some cases to severe structural instability. This paper focuses on the oldest group of rock reliefs, dating back to the Achaemenian period; due to their location on the top of a sloping cliff, they are less accessible and more challenging by a conservation point of view. The reliefs have been studied in field and by means of a multi-analytical laboratory procedure, in order to identify the decay patterns, along with an assessment of the state of conservation. In order to frame the problem in a proper historical context, archival material including photographs, drawings and descriptions - created on purpose by western scholars between the 17th and the 20th century - are also analyzed focusing on any indications as regards deterioration problems. Fragments were sampled from the upper bed rock, from layered formations, surface deposits, and from areas with biological growth. They were studied by means of optical microscopy, SEM-EDX and XRD analyses. The results show that the main decay features could be classified as Concretion, Deposit, Bio-film, Detachment, Crust, Oxalate film and Cracks. Among the main decay causes and mechanisms, the chemical dissolution of the stone substrate and the heavy microbiological subsurface growth play a major role. The layered aluminosilicate encrustations imply a continuous exposure of the limestone monument to the moisture ingress from the outer environment. Also, indications of the recent impact of atmospheric pollutants were observed, which is noteworthy, considering the distance of the monument from the urban areas.
Study of decay patterns and damage assessment of the Achaemenian rock-reliefs of Naqsh-e Rustam
Sansonetti A;Biondelli D
2020
Abstract
Ancient rock reliefs in the necropolis of Naqsh-e Rustam are important testimonies of the development of an outstanding monumental art over the centuries, in close relationship with their natural context. The rock reliefs underwent natural and anthropic decay processes in the course of time, which caused dramatic changes affecting their aspect, leading to the loss of fragments and in some cases to severe structural instability. This paper focuses on the oldest group of rock reliefs, dating back to the Achaemenian period; due to their location on the top of a sloping cliff, they are less accessible and more challenging by a conservation point of view. The reliefs have been studied in field and by means of a multi-analytical laboratory procedure, in order to identify the decay patterns, along with an assessment of the state of conservation. In order to frame the problem in a proper historical context, archival material including photographs, drawings and descriptions - created on purpose by western scholars between the 17th and the 20th century - are also analyzed focusing on any indications as regards deterioration problems. Fragments were sampled from the upper bed rock, from layered formations, surface deposits, and from areas with biological growth. They were studied by means of optical microscopy, SEM-EDX and XRD analyses. The results show that the main decay features could be classified as Concretion, Deposit, Bio-film, Detachment, Crust, Oxalate film and Cracks. Among the main decay causes and mechanisms, the chemical dissolution of the stone substrate and the heavy microbiological subsurface growth play a major role. The layered aluminosilicate encrustations imply a continuous exposure of the limestone monument to the moisture ingress from the outer environment. Also, indications of the recent impact of atmospheric pollutants were observed, which is noteworthy, considering the distance of the monument from the urban areas.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
