Please cite this article in press as: M. Goleˇ z, et al., Laboratory-prepared lime-gypsum mixtures based on the know-how of traditional technology, Journal of Cultural Heritage (2017), https://doi.org/10.1016/j.culher.2018.02.011 ARTICLE IN PRESS G Model CULHER-3358; No. of Pages 6 Journal of Cultural Heritage xxx (2017) xxx–xxx Available online at ScienceDirect www.sciencedirect.com Original article Laboratory-prepared lime-gypsum mixtures based on the know-how of traditional technology Mateja Goleˇ z a,∗ , ˇ Zeljko Pogaˇ cnik b , Ana Mladenovi ´ c a a Slovenian National Building and Civil Engineering Institute, Dimiˇ ceva 12, 1000 Ljubljana, Slovenia b Georudeko, d.o.o, Anhovo 1, 5210 Deskle, Slovenia a r t i c l e i n f o Article history: Received 11 September 2017 Accepted 19 February 2018 Available online xxx Keywords: Gypsum Quicklime Suspension Facade Cultural heritage a b s t r a c t Stratigraphically, the oldest layer of paint which was applied to the facade walls of the Novo Celje Baroque Mansion contains substantial amounts of gypsum, as well as calcium carbonate and iron pig- ment. Microstructural, isotopic, and thermal analyses of facade samples were performed in order to exclude the possibility of an anthropogenic source of gypsum crystallisation, and to prove that natural gypsum was used to prepare the original lime-gypsum suspension. This is because, in the exothermic process of quicklime hydration, natural gypsum is converted into ß-hemihydrate and then, after cooling of the suspension, this compound is converted back into gypsum. The technology which was used for the laboratory-level preparation of the investigated lime-gypsum suspensions is simple, efficient, and sustainable, and could thus be used instead of the more energy-consuming dehydration processes which are presently used in the industrial production of gypsum. © 2018 Elsevier Masson SAS. All rights reserved. 1. Research aims With regard to the technical issues which are involved in the renovation of historical materials, the presence of gypsum crys- tals is a phenomenon which is frequently attributed to the reaction between acid rain and the lime binder (i.e. secondary gypsum), and not to a primary building material (e.g. natural gypsum). The results of recent research into the properties of historical materials have shown that primary and secondary gypsum can be distinguished based on the identification of strontium, which is a characteristic of primary gypsum, but is not to be found in the secondary crystallisa- tion products of gypsum. Strontium is an interesting marker which has already been used to prove the source of gypsum in historical materials [1], which is why it was also used in this research to con- firm the source of gypsum as a natural resource for the preparation of lime-gypsum suspensions. In modern industrial applications, thermal energy is used to dehydrate gypsum into -hemihydrate. For this reason a hypothe- sis was established according to which, during the Baroque period, lime-gypsum suspensions were prepared by master builders in a manner which allowed them to take advantage of the exothermic reaction which takes place during lime slaking, and which also takes ∗ Corresponding author. E-mail addresses: mateja.golez@zag.si (M. Goleˇ z), zeljko.pogacnik@georudeko.si ( ˇ Z. Pogaˇ cnik), ana.mladenovic@zag.si (A. Mladenovi ´ c). place if a mixture of quicklime and gypsum is slaked. It was taken into account that, during this period, the building material industry was not as highly developed as it is today, nor was thermal energy so easily accessible. The technology which was used to prepare lime-gypsum sus- pensions was experimentally simulated in a similar manner to that used in the Baroque period, which can be concluded from the results of the investigations of one of the facade walls of the Novo Celje Baroque Mansion, the latter being one of the most typical such buildings belonging to this period in Slovenia. 2. Introduction The Novo Celje Baroque Mansion is an impressive building which is located in the central part of Slovenia. It was built accord- ing to instructions given by Maria Theresa, the Austro-Hungarian Empress, for her Minister, Count Geisruck, between 1756 and 1764 [2]. After having been abandoned for more than two decades, conservation guidelines for the Mansion’s renovation have been prepared by the Celje Regional Office of the Institute for the Pro- tection of the Cultural Heritage of Slovenia (IPCHS), according to which, after the renovation works are completed, the facade walls will once again obtain their yellow-ochre Baroque appearance (Fig. 1). For this purpose the layers of paint of one of the facade walls of the Novo Celje Baroque Mansion were analysed in detail. The https://doi.org/10.1016/j.culher.2018.02.011 1296-2074/© 2018 Elsevier Masson SAS. All rights reserved.