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Analysis of over 180 historical documentary sources from 1600 to 1900 covering the cleaning of oil paintings established that the use of alkalis was mentioned in over 50% of references to aqueous cleaning. Alkalis could be employed as a paste with wood ashes and water or in the form of lye. Historical alkali cleaning recipes based on wood ashes were reconstructed and characterised using titration and in- ductively coupled plasma-atomic emission spectroscopy (ICP-AES). Results indicate that pH depends on the wood-ash source, the age of both the ashes and the lye, as well as on the proportion of ash to water. Reconstructions of lye solutions and wood-ash pastes were applied to naturally aged model oil paints and oil paintings. Their visual impact was investigated using high resolution imaging, and chemical changes were studied with infrared spectroscopy in attenuated total reflection (ATR-FTIR) and focal-plane array Fourier transform infrared spectroscopy (FTIR-FPA) as well as scanning electron microscopy equipped with energy-dispersive X-ray analysis (SEM-EDX). These latter investigations determined the presence of potassium within the upper layers of paint samples after exposure to wood ash lye. The potassium remained in the oil network after extensive water rinsing. This research adds information to our existing knowledge about historical cleaning methodologies and contributes to a better understanding of the current condition of paintings previously cleaned with alkalis.

A new pigmented wax-resin formulation introduced and tested for its suitability as a material to infill and reintegrate losses in paintings. This formulation contains Cosmoloid H80 microcrystalline wax and Regalrez® 1126 hydrogenated hydrocarbon resin, in a ratio of 1.5:1 (wax:resin, parts by weight), and is mixed with dry pigments and/or inert fillers (such as chalk, kaolin, or aluminium hydroxide). After extensive research on the properties and the stability of various formulations, the most successful one was applied on two canvas paintings with very diverse characteristics: a 17th century oil painting, and a 21st century acrylic painting. In this paper, the different application methods used are described step-by-step. These consisted of using the new formulations not only solely as infilling materials (by adding inert fillers to the wax-resin mixture), but also as materials capable of infilling and reintegrating a loss in one single step (by adding pigments to the wax-resin mixture). The possibility of imprinting and carving texture, as well as of sculpting the infills to recreate brushstrokes, was also tested and verified and is described in detail here.

The relationship between artists’ material choices, the preparation and application of materials, and the consequences – the appearance and material properties of the art-work – are studied using Historically Accurate Reconstructions Techniques (HART). This model provides a systematic means to evoke past practices. Reconstructions focus on a range of topics, from the flow properties of Van Gogh’s paint to the colour of natural chalk used in artists’ preparation layers. As the operator physically prepares and uses the materials, the steps towards the moment of painting are re-enacted. The products of the re-enactment, the documentation and the reconstruction itself, provide evidence – visual, physical and chemical ‒ for comparison with historic oil paintings.

As autoras agradecem ao Ecomuseu Municipal do Seixal a oportunidade de realizar este estudo, nomeadamente à Dr.ª Ana Duarte e a José Meias pela grande disponibilidade e ajuda ao longo de todo o projecto. As autoras agradecem também a Stefan Michalski por ter apresentado o conceito de Garry Thomson de utilizar sílica-gel como um sistema passivo de redução das flutuações diárias e anuais de HR, no início de 1980, durante discussões com uma das autoras, a propósito do design de uma moldura microclimática para uma pintura sobre tela [28]. Este artigo foi escrito com o apoio das bolsas de doutoramento ref.ª PD/BD/135054/2017 (Sara Sá) e ref.ª PD/BD/135058/2017 (Raquel Marques) da Fundação para a Ciência e Tecnologia (FCT-MEC) e com o apoio do Laboratório Associado para a Química Verde – Tecnologias e Processos Limpos (LAQV) financiado por fundos nacionais através da FCT/MCTES (UID/ QUI/50006/2013) e co-financiado pelo FEDER, no âmbito do Acordo de Parceria PT2020 (POCI-01-0145-FEDER-007265). Ecomuseu Municipal do Seixal is aiming to exhibit three oil portraits on canvas from the 19th century in the Tide Mill of Corroios. Due to its location, intrinsic to its function of Tide Mill, the building exhibits environmental conditions characterized by severe fluctuations in temperature and relative humidity. This work aims to propose a model of microclimate frame that offers a solution for the continued preservation of the three paintings. The frame’s design was chosen based on the study of the environmental conditions (temperature and relative humidity) of the exhibition room at the Tide Mill as well as in the results of an in situ experiment involving model frames. The proposal here described, a microclimate frame with silica gel as buffering material, considered the designs presented in the literature, the individual needs of the paintings and, finally, the available budget. publishersversion published

Dans cette étude sur la technique de la peinture sur cuivre, 18 sources historiques, dans six langues différentes, datant du 17e et 18e siècle ont été rassemblées, permettant de systématiser la plupart des informations sur des matériaux utilisés et des techniques de mise en œuvre sur ce type de peintures. Douze peintures de la période mentionnée ci-dessus ont été étudiées et comparées avec la littérature historique. In this research about painting on copper technology, 18 historical sources, covering six different languages, dated from the 17th and 18th centuries were collected, allowing to systematise most information about materials and techniques applied on these sorts of paintings. Twelve paintings from the same period mentioned above were studied and compared with the historical literature.