Low-risk removal of embedded surface soiling on delicate heritage objects can require novel alternatives to traditional cleaning systems. Edvard Munch’s monumental Aula paintings (1911–16) have a long history of exposure to atmospheric pollution and cleaning campaigns that have compromised the appearance and the condition of these important artworks. Soiling removal from porous and water-sensitive, unvarnished oil paintings continues to be a major conservation challenge. This paper presents the approach and results of research into the effect and efficiency of three novel systems used for soiling removal: soft particle blasting, CO2-snow blasting, and Nanorestore Gel® Dry and Peggy series hydrogels. Cleaning tests were performed on accelerated-aged and artificially soiled mock-ups consisting of unvarnished oil paint and chalk-glue grounds. Visual and analytical assessment (magnification using a light microscope and scanning electron microscope, as well as colour- and gloss measurement) was carried out before and after mock-up cleaning tests and the results were compared to those obtained using the dry polyurethane sponges employed in the most recent Aula surface cleaning campaign (2009–11). Although the results varied, the Nanorestore Gel® series proved promising with respect to improved soiling removal efficiency, and reduced pigment loss for the water-sensitive surfaces evaluated, compared to dry sponges.

The availability and popularity of portable non-invasive instrumentation for the study of paintings has increased due to a shift away from using micro-invasive techniques. Fourier transform infrared spectroscopy (FTIR) is a successful and established technique for the characterisation of organic materials in varnish coatings and paint films. In addition, portable FTIR (pFTIR) spectrometers allow for non-invasive in situ analyses. This overcomes the disadvantages associated with micro-sampling and reproducibility issues encountered in analysis at a specific spot, as pFTIR enables examination of the whole painting. However, the practical applications and capabilities of pFTIR as a suitable screening method for the chemical characterization of varnish coatings in painting collections require systematic evaluation. This study involves a selection of three paintings from the collection of 57 works by Edvard Munch belonging to The National Museum of Art in Norway. Its focus is the identification of the non-original varnish types that were applied by the museum. Between 1909 and 1993, the Museum was embroiled in a varnish controversy due to their application of, first natural and then synthetic, varnish coatings to 48 of these Munch paintings. A series of public debates arose about the Museum's varnishing practice, which ran counter to the artist's usual custom of leaving paint surfaces unvarnished (or occasional locally varnished). The three paintings were screened using a pFTIR spectrometer. Different regions of the varnished and unvarnished painted surfaces were analysed with Portable Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). These paintings date from 1887 to 1891 and are documented as having been treated at the Museum with one of the following types of natural or low-molecular-weight synthetic varnish coatings: dammar, mastic, polycyclohexanone (Laropal K 80 from BASF) and reduced or hydrogenated cyclohexanone-co-methyl-cyclohexanone (MS2A from Howards of Ilford). Surface microscopy and multispectral imaging of the varnished surfaces initially assisted the mapping and choice of areas relevant for the portable DRIFTS measurements. Portable X-Ray fluorescence and surface gloss readings were also made at the pFTIR spot locations to complement the results. Using known dry varnish samples, pFTIR reference spectra were obtained and a DRIFT spectral library was also created from known historic batches of varnishes used by the museum. These were then compared with the in situ pFTIR surface readings taken from the paintings together with additional spectra acquired from a selected number of micro-samples from the same spot locations. The preliminary measurements provided an insight into the capabilities, limitations and practical aspects of using portable DRIFTS for the identification of varnish coatings present in this specific selection of Munch paintings.

Micro-samples from 57 original paint tubes used between 1904 and 1909 by the Norwegian painter, Harriet Backer were studied with inductively coupled plasma-optical emission spectroscopy (ICP-OES). This accurate elemental characterisation of Backer's original materials aims to fill several gaps in conservation science, painting conservation, and art technology. Firstly, it provides a novel and validated analytical method that can be applied to other painting materials. Secondly, ICP-OES offers scientific information about different oil colours from the late 19th to the early 20th century by Dr. Schoenfeld & Co., Düsseldorf, currently known as Lukas-Nerchau, whose archives were depleted during the Second World War. This work also lends new insights into the paintings of a renowned female Norwegian artist, whose painting materials have been little studied to date. ICP-OES results, coupled with a comprehensive, illustrated catalogue of paint tubes, will be instrumental for ongoing scientific investigations of this painter's body of work.

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