Characterizing degradation in the decorative finish of two case-studies:
Sint Pietershof Hoorn and Weeshuis der Hervormden Schiedam.*
In the Netherlands a considerable amount of 18th century gilt leather hangings has been preserved ‘in situ’. For the past decade heritage professionals have raised great concern about their material condition, as several hangings locally show severe darkenings. These degradations have been registered in at least eight locations in the Netherlands, but are expected to be more widespread. Conservators and interior specialists suggest that the dark stains may be the result of past conservation treatments with oil dressings and emulsions, during the second half of the twentieth century.
A systematic description and characterization of this darkening has been started by examining two examples of Dutch 18th century gilt leather hangings: Sint Pietershof, Hoorn and Weeshuis der Hervormden, Schiedam. A literature and archive review of the products used in gilt leather conservation during the past decades has been undertaken, allowing a better understanding of the relationship between past conservation treatments and the observed degradations.
Analyses of the different layers of the decorative ‘golden’ finish have been carried out – consisting of a silver leaf applied with a parchment glue and coated with an oil-resin varnish (‘golden varnish’). Visual observations of the degradation phenomena have been complemented by comparing cross-sections of un-darkened and darkened gilt leather samples, using light microscopy, SEM-EDX and GC-MS. The results indicate that degradation processes related to the darkening are taking place in both the silver and varnish layers.
This study is a first step in identifying the degradation phenomena that occur in the decorative finishes of gilt leather hangings, which can be related to past conservation treatments. The irreversible character of the degradations in both silver and varnish layers, underlines the importance of further identification of the degradation mechanisms and the role of climatic conditions, such as relative humidity, moisture and gaseous pollutants. Eventually, this will contribute to the development of preventive conservation measures for gilt leather hangings ‘in situ’ that are known to have undergone oil treatments in the past.
Publication of this work is in preparation.
Awarded the Prize for Best Master Thesis by Rijks Museum Amsterdam and the Dutch Cultural Heritage Agency 2012.
Elizabet Nijhoff Asser, independent leather and paper conservator-restorer, Amsterdam.
Katrien Keune, Conservation Scientist, Cultural Heritage Agency of the Netherlands, Van ‘t Hoff Institute for Molecular Science (HIMS), University of Amsterdam.
Danielle van Kempen, Lecturer Conservation and Restoration of Historic Interiors, University of Amsterdam.
The author gratefully acknowledges Dutch Cultural Heritage Agency (RCE) and Rijks Museum for facilitating technical analysis, Sint Pietershof Hoorn and Vereniging Hendrick de Keyser for the accessibility of the gilt leather hangings.
* This is an abstract of the presentation at the Joint Meeting in Breda in october (http://wp.me/pLSqf-16H) of research by M. Posthuma de Boer (MA Conservation and Restoration of Historic Interiors, University of Amsterdam)