The use of mortars and plasters has been widespread in many cultures for thousands of years and these materials are found in the vast majority of built cultural heritage. They play a crucial role in the preservation of immovable heritage and must be taken into great consideration when conserving historical buildings. Plasters and mortars have been extensively studied from a chemical and mineralogical point of view. The main causes and mechanisms of damage and deterioration are understood and various methods and materials have been developed for their preservation. Treatment development, testing and evaluation in the laboratory, under controlled conditions, has produced a high level of knowledge. However, there is a divergence between the results of academic-scientific studies and practice in the field. Laboratory studies typically tackle only a few variables at the time and the results cannot always be directly applied to address the complex problems that restorers face in their daily work practice. In addition, in situ conservation-restoration is extremely challenging because many of large number of variables involved cannot be controlled or modified. Following a description of the ideal “value-based” conservation process, this compilation work discusses aspects related to understanding deterioration mechanisms and planning of preventive and remedial interventions in a way that may be useful to update conservators-restorers on the status of scientific research in this field, and to guide conservation-scientists to identify unresolved issues, which require future research efforts.

Ochre-based pigments have been employed since the first artistic expressions of mankind, with widespread diffusion during the Roman civilization. Such prominent use influenced their technological development, focused on functional and aesthetic optimization through complex manufacturing procedures. Furthermore, their appearance is also influenced by degradation processes, sometimes driven by natural disasters such as the eruption of Mount Vesuvius in 79 AD, in which yellow ochres of Vesuvian sites were sometimes converted to red by thermal alteration. In this contribution, a multi-analytical approach was adopted based on preliminary non-invasive investigations complemented by laboratory analyses to characterize the painted surfaces of the tablinum of the House of the Bicentenary (Herculaneum) with a particular focus on the ochre-based monochrome backgrounds. The study was aimed at (a) reconstructing the original color scheme of the walls and (b) deciphering the complex decorative techniques adopted by Roman craftsmen. The analytical results allowed testing and defining analytical procedures for the discrimination between the original and converted red pigments. Furthermore, these studies indicated that specific decorative technologies were adopted according to aesthetic, functional, and economic purposes, including the utilization of various qualities of ochre with different compositional and textural properties, and the mixture of ochre pigments with other compounds.

The Château de Germolles is one of the rare palace in France dating from the 14^th century. The noble floor is decorated with wall paintings that are a unique example of courtly love spirit that infused the princely courts of the time. After being concealed sometime in the 19^th century, the paintings were rediscovered and uncovered in the middle of the 20^th century and partly restored at the end of the 1990s. No scientific documentation accompanied these interventions and important questions, such as the level of authenticity of the mural decorations and the original painting technique(s) used in the medieval times remained unanswered. The combined scientific and financial supports of COSCH Cost Action and DRAC-Burgundy enabled to study Germolles’ wall paintings using some of the most innovative imaging and analytical techniques and to address some of the questions raised. The study provided significant information on the material used in the medieval times and on the conservation condition of the paintings. The data collected is vast and varied and exposed the owners of the property to the challenges of data management.

The modern decoration of the Saint Nicolas de Myre Church at Semsales (1924–1926), is the first by renowned Italian artist Gino Severini in Switzerland. Following archival research and visual examination, the materials and the techniques used by Severini for the wall paintings of this church were examined through a multi-technique analytical approach that included both non-invasive and invasive investigations. Archival research revealed lists of some of the materials purchased for the church and notes of the artists. In situ investigations included imaging methods and point analyses (X-ray fluorescence and reflection FT-IR spectroscopy). Based on non-invasive results, a limited number of representative samples were collected for laboratory invasive analyses (SEM-EDS, FTIR-FPA imaging, μ-Raman and GC-MS) to characterize the stratigraphy and the composition of the paintings. Results were coherent with artist’s notes and revealed protein-based binders, i.e. animal glue and casein, exclusively on the Trinity mural (in the apse) confirming the use of a secco technique. All the other wall paintings analyzed at Semsales are painted without the use of organic binders. These findings, integrated with archival researches and the visual examination by conservators, provided significant insights into the materials and techniques used by Gino Severini in his first Swiss murals.

Conventional grouting – used to stabilise delaminated plaster – typically involves the use of water as suspension medium. Water can be dangerous when water-sensitive original materials are present and can cause the solubilisation of salts, leading to their re-crystallisation on drying. Ethyl alcohol is a less effective solvent for soluble salts and generally does not affect the original materials. This is the reason why it was used as a partial substitute for water in grout preparations in the present research. Three water–ethyl alcohol-based grouts were compared with the correspondent water-based grout. The working properties and performance characteristics of the injection grouts with reduced water content were measured to assess their suitability for use on historic plasters.

Although Gino Severini is recognised as a leading exponent of European avant-garde movements through the first half of the twentieth century, his work as a mural painter is little known. This article reports the technical study of Severini’s wall paintings for the Swiss church of Saint Nicolas de Myre in Semsales (1924–1926), in the framework of a research project coordinated by the University of Applied Sciences and Arts of Southern Switzerland and financed by the Swiss National Science Foundation. Taking an interdisciplinary approach, the project investigates the wall paintings made by the artist in five churches in Switzerland and dating between 1924 and 1947, with the aim of clarifying the artist's mural painting techniques. Following research in the parish archives and in those of the Severini family, the project proceeded in the different churches with in situ examination (diffuse and raking visible light, UV radiation, digital microscopy) supported by non-invasive scientific investigation (technical photography and spectroscopic point analyses) and laboratory invasive analyses on micro-samples. Lastly, the data from all the various sources are collected and interrelated. The artist’s first commission, in 1924 at Semsales, became the longest and most complex, given the artist’s relative lack of mural experience, the extent of surfaces, and variety of techniques adopted. The investigation reveals a long process in which Severini mastered a secco procedures using organic binders, on plasters that had already been applied, flanked by works in the tradition of a fresco painting, enriched with a modern palette of colours. Underlying all this work was a long process of planning, in which the artist associated the differing techniques with variations in style, in an extremely personal language between cubism and classicism.