JAIC 1987, Volume 26, Number 2, Article 4 (pp. 105 to 120)
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Journal of the American Institute for Conservation
JAIC 1987, Volume 26, Number 2, Article 4 (pp. 105 to 120)


Mark Gilberg


In addition to his efforts on behalf of the Royal Museums of Berlin, Rathgen displayed a keen interest in the care and preservation of historic buildings and monuments. Over the years the preservation of building stone increasingly became the main focus of his attention. In many respects this was a natural extension of his research on the conservation of archaeological stone. Many if not all of the treatment methods employed for the conservation of stone antiquities had originally been developed for the preservation of weathered building stone. Although Rathgen's pioneer work in architectural preservation was overshadowed by his accomplishments in the field of archaeological conservation, his contributions were nonetheless considerable.

Rathgen took great care in the design of his experimental trials to ensure the reliability and accuracy of the results. In all his experimental trials Rathgen sought to duplicate as much as possible the exact conditions under which weathering would occur. In this respect he was extremely wary of any data gathered from short-term trials conducted in the laboratory which attempted to simulate the process by which stonework was assumed to decay. Rathgen maintained that meaningful results could be obtained only from the analysis of stonework treated in situ and subjected to weathering over a prolonged period of time.

As early as 1902 Rathgen was conducting experimental trials on the use of fluorosilicates for the preservation of marble (Rathgen, 1906). He had previously employed fluorosilicates for the consolidation of porous and friable limestone antiquities with great success. Samples of marble were impregnated with fluorosilicates and then left to weather naturally in three different locations in Berlin.

Unfortunately, when the samples were examined several years later it was not possible to assess the difference between the fluorosilicate-impregnated samples and the unimpregnated samples due to the limited number of samples tested and the rather brief test period.

These tests were expanded in 1907 in order to compare the relative effectiveness of a variety of commonly employed stone preservative solutions. In initial studies representative samples of German building stone were impregnated with various stone preservative solutions and then placed in specially constructed glass cases on the roof of the museum. The cases were constructed such that only one surface of the stone, protruding one to two millimeters above the edge of the glass, was exposed to the atmosphere. The surface of the stone itself was inclined towards the horizontal at an angle of approximately 6° facing west. In this manner Rathgen sought to mimic the exact conditions under which the weathering of building stone naturally occurs. Overall, eleven different stones were tested including thirty-eight marble, seventy-three limestone, and one hundred forty-four sandstone samples. The samples were examined every two years to record changes in their appearance and to determine their loss in weight. With the receipt of a large grant from the Jagorstifung in 1911, similar trials were conducted in Hamburg, Köln and Schleswig and expanded to include other commonly employed building stones and stone preservative solutions.

The results of Rathgen's experimental trials were published in a series of seven communications between the years 1910 and 1924 in the German building journal Zeitschrift für Bauwesen (Rathgen, 1910, 1913, 1915, 1916, 1919, 1920, 1922). They were subsequently reviewed in three short communications published in Tonindustrie-Zeitung (Rathgen, 1917). In general, Rathgen found that no one stone preservative preparation was completely effective in preventing the decay of all types of building stones and that different stones required different treatment.

In 1926 Rathgen published a compilation of all studies conducted up to that time on the care and preservation of outdoor bronze sculptures. Particular attention was given to the mechanism by which the patina was formed on the sculptures and the relationship between it and the chemical composition of the bronze alloy (Rathgen, 1926). A card index was prepared cataloguing the patina of approximately nine hundred bronze monuments, thus providing an excellent survey of the changes that had occurred over the years.

In 1934 in collaboration with J. Koch, Rathgen published a monograph entitled Verwitterung und Erhaltung von Werkstein: Beiträge zur Frage der Steinschutzmittel [Deterioration and Preservation of Building Stone: Contributions to the Problem of Stone Preservatives], in which he summarized much of his previous work with regard to the preservation of building stone. The monograph was divided into five parts. In Part I Rathgen presented the results of a series of experimental trials conducted a number of years earlier in which he treated a number of historic buildings with various stone preservative solutions. Just prior to World War I the Ministry of Public Works, in conjunction with the Ministry of Church and Education, appointed a commission to consider the unusually rapid decay of many of the public buildings and monuments in Prussia at that time and to suggest means for arresting the decay. Under Rathgen's supervision a series of experimental trials were conducted whereby portions of the stonework of various monuments and buildings, both old and new, were treated with a number of different stone preservative preparations. The stone blocks were treated in situ and identified with chisel marks. Every three years the blocks were examined and photographed together with one or several controls. Initially the trials were confined to Berlin, Breslau, Danzig, Emden, Frankfurt/Main, Halle an der Saale, Köln, Magdeburg, Münster, Posen and Wetzlar, though they were subsequently expanded to include Altona, Hamburg, Heidelberg, Karlsruhe, München, and Stuttgart.

The trials, which were initiated in 1911, were not concluded until 1928, and though interrupted by the outbreak of World War I, by 1917 over one thousand, two hundred fifty-seven blocks had been examined. In his final report Rathgen presented his experimental findings in tabular form giving the building or monument treated, the location from which the stone was quarried, the stone preservative employed and the date of its first application, the date at which the first sign of decay was observed and the form it took and the state of preservation of the treated stone when examined in 1926.

In Part II of his Handbook Rathgen published the results of his examination of a number of historic buildings and monuments which had previously been treated with a variety of stone preservative solutions as part of a study conducted by the Königlichen Sachischen Kommission zur Erhaltung der Kunstdenkmaler [Royal Saxon Commission for the Preservation of Monuments of Art] during the late 19th century. The tests were conducted between 1896 and 1905 and the results published in 1907. In 1929 Rathgen and Koch visited a number of the cities in Saxony where the original experimental trials were conducted, noting the extent and progress of the decay of the treated stone. Though he had difficulty identifying those portions of the building that had been treated, Rathgen was able to examine over fifty-five buildings in twenty cities in Saxony.

In Part III Rathgen reviewed his earlier experimental trials comparing the relative effectiveness of various stone preservative preparations.

Part IV was devoted to the deterioration of the stonework of the Marienkirche in Gelhausen.

In Part V Rathgen synthesized much of the aforementioned material in his concluding remarks.

In 1939 Rathgen and Koch published a second handbook entitled Merkblatt für Steinschultz [Notebook for Stone Protection] (Rathgen, 1939).

Copyright © 1987 American Institute for Conservation of Historic and Artistic Works