The marble sculptures of General B\xfclow and Scharnhorst in Berlin: comparative, non-destructive analysis of the weathering state after 12\xa0years of exposure

J Menningen,R Krompholz,Y Rieffel,S Siegesmund

doi:10.1007/s12665-020-08984-7

Abstract

After almost 200 years of exposure, the monuments of General Scharnhorst and Bülow have been analysed by means of ultrasound. Both sculptures are made of Carrara marble, both sculptures have been exposed to the same environmental influences and both sculptures are, based on the results of the ultrasonic measurements, in alarming conditions. This statement can be made because of the data of three different measurement investigations within the last 12 years. In this short exposure time, the already low velocities have been reduced by 16.2% and 14.7%. The very low average velocity of 2.8 km/s for the sculpture of General Bülow and a slightly higher average velocity of 3.2 km/s for the Scharnhorst sculpture indicate that both sculptures are in a poor condition, even though a protective winter shelter has been used since 2004. Comparing tomographic velocity measurements performed in 2006 with the measurements made in 2018 was possible and showed that even areas with a thickness up to 90 cm show alarming low ultrasonic velocities down to 2.6 km/s. Even if the circumstances for both sculptures have been the same, they differ in their weathering state. The careful and transparent documentation of all measurements was in this context the most important aspect for the comparative studies. Irregularities in their weathering behaviour of the two statues can be distinguished, allowing an in-depth analysis of the deterioration of the marble.

Highlights

Crystalline marble shows a very special weathering behaviour in contrast to other natural stones
He continued to address this hypothesis by determining significantly lower ultrasonic velocities at different depth ranges on a highly decayed marble capital from the Freundschaftstempel (Temple of Friendship) in Potsdam, Sanssouci, where he observed a higher variation in ultrasonic wave velocities
Köhler (1991) established a decay classification for marble, which connects decreasing compressional wave velocities with an increasing state of decay. This decay/velocity classification allows determining whether a marble sculpture can only be preserved by applying ongoing conservation measures

Summary

Introduction

Crystalline marble shows a very special weathering behaviour in contrast to other natural stones. On the basis of these observations, Köhler (1988) defined the concept of inner or core weathering as a special form of damage. He continued to address this hypothesis by determining significantly lower ultrasonic velocities at different depth ranges on a highly decayed marble capital from the Freundschaftstempel (Temple of Friendship) in Potsdam, Sanssouci, where he observed a higher variation in ultrasonic wave velocities. Köhler (1991) established a decay classification for marble, which connects decreasing compressional wave velocities with an increasing state of decay This decay/velocity classification allows determining whether a marble sculpture can only be preserved by applying ongoing conservation measures. This is generally the case when the ultrasonic velocities for the compressional waves show magnitudes less than 3 km/s for most of the investigated directions ( Snethlage et al 1999; Siegesmund et al 2004; Siegesmund and Dürrast 2014)

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Discussion

Conclusion