The identification of damaging soluble salts is at the forefront of Conservation sciences as they can threaten the existence of a wide range of objects. Depending on many external factors, but often also due to the components of the material itself, the harmful salts must be analysed with regard to their composition, crystal form, quantity and the exact position in the pore space or on the surface of the damaged object in order to identify the cause or to plan the possibilities for their removal or mitigation.
In keeping with the importance of the problem, there has long been active international research and publication activity on the subject of harmful salts (see also The Salt Wiki). The main focus of our department is the analysis of salt crystals with light and scanning electron microscopes in relation to the substrate in which they grow or in whose pores and cracks they are crystallized. These results are combined with the results of quantitative ion analysis, which are carried out by our cooperation partners - mainly the Natural Science Laboratory of the Federal Office for Monument Preservation, Dr. Farkas Pintér - and evaluated by us on an object-related basis. This combination of qualitative and quantitative analyses allows for the best description of the problem and informs its restoration.
If preventive conservation is the goal by means of climate-controlled deactivation of salts in order to prevent their dissolution and crystallization cycle, then it all depends on a series of further investigations. Sorption isotherms are measured gravimetrically in our climate chamber, while an alternative way of observing phase transformations and hygroscopic dissolution has recently been pursued in a miniature climate chamber under the microscope. Last but not least, we also focus on monitoring the object itself in order to be able to detect all relevant changes in the salt system during the course of the seasons.
Our department's most comprehensive monitoring project to date was dedicated to the interior of the underground Virgil Chapel in Vienna's city centre, where we were commissioned by the Wien Museum to develop the key data for the best possible climate control to stabilize the enormous quantities of efflorescent salts.
The detection of harmful salts continues to be a frequent topic of our work, one that we strive to improve and further develop while constantly being mindful of the needs of restoration and conservation. To go beyond the routine of standard salt analysis is necessary for a university institute with a research commission. Since the questions should mostly come from practice, however, we are in the fortunate position of being confronted with interesting problems by the relevant institutes of applied arts and the Academy of Fine Arts Vienna as well as by restorers, monument offices and museums. Recently, two extensive seminar papers at the Institute for Conservation and Restoration of the Vienna Academy of Fine Arts are worth mentioning here, which we have been able to supervise in essential parts and whose empirical values we are allowed to use.
J. Flaschberger: Multi-component clay mineral compresses for salt extraction - Physical properties and practical application of systematically developed compress formulations (2014)
J. Knollmayr: Microscopy as a method to study the moisture behaviour of harmful salts under defined relative humidity (2019)