Evaluation of three Italian tuffs (Neapolitan Yellow Tuff, Tufo Romano and Tufo Etrusco) as compatible replacement stone for Römer tuff in Dutch built cultural heritage
Timo G. Nijland, Rob P. J. Van Hees, Laura Bolondi, 2010. "Evaluation of three Italian tuffs (Neapolitan Yellow Tuff, Tufo Romano and Tufo Etrusco) as compatible replacement stone for Römer tuff in Dutch built cultural heritage", Natural Stone Resources for Historical Monuments, R Přikryl, Á Török
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Rhenish tuffs from the volcanic Eifel region in Germany, in particular the so-called Römer tuff, are among the most prominent and voluminous natural stones in Dutch monuments. The Römer tuff has been used since Roman times, and was widely used again in Romanesque (and to a lesser extent Romano-Gothic and early Gothic) architecture. The limited (or non) availability of Römer tuff for restoration purposes is posing an increasing problem. Last decennia, the availability of Römer tuff was practically limited to blocks from the lower parts of the pyroclastic flows with abundant basalt (and other) xenoliths, giving the rock a different appearance from its traditional type; the different types of Römer tuff also demonstrate different physical and hygric properties. Given the wide use of tuff stone in Italian architecture, several Italian tuffs have been evaluated in search of a compatible replacement stone for Römer tuff. The replacement stones should approach the original as much as possible, that is, in terms of authentic appearance, physical characteristics and durability. The Italian tuffs evaluated include tuffs commercially denominated as Tufo Etrusco and Tufo Romano (from the central part of Italy) and a variety of Neapolitan Yellow Tuff (Naples region). Hygric behaviour, resistance to frost-thaw cycles, petrographic characteristics and mineralogy of Italian tuffs have been determined and compared with original Römer tuff. In all three cases, resistance to frost-thaw cycles is unfortunately shown to be considerably less than that of original Römer tuff. In addition, hygric expansion of the Neapolitan Yellow Tuff appeared to be considerably larger than that of original Römer tuff. Of the tuffs evaluated, the variety of Neapolitan Yellow Tuff is a good match with the original Römer tuff in terms of visual appearance. It has already been sparsely used in the Netherlands in minor amounts. However, the durability characteristics require additional evaluation.
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Natural stone is considered to be a versatile, durable and aesthetically pleasing building material. From the beginning of civilization, important structures and monuments have been built from, or based on, natural stone. Until the end of the nineteenth century, the use of local stone resources was mostly in balance with the local environment. Strict environmental legislation has resulted in the closing of many long-standing quarries in industrialized countries, which has led to a shortage of traditional stone varieties. This has caused problems for restoration practice. Cheap, imported stone from less industrialized countries has become more widely available in recent years.
Some of the issues related to built stone conservation and restoration covered by this volume are: the establishment of inventories of possible replacement stones; understanding the decay mechanism and use of preventive conservation methods for slowing down decay processes; evaluation of the properties of natural stone; and assessing the risks of using replacement stones of different qualities.