Lanterna Mágica - Technology and preservation of painted glass slides for projection with Magic Lanterns

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Production of Hand-painted Magic Lantern Glass Slides

Publication . Santos, Ângela; Otero, Vanessa; Vilarigues, Márcia; DCR - Departamento de Conservação e Restauro; VICARTE - Vidro e Cerâmica para as Artes; LAQV@REQUIMTE; Earthscan

Hand-painted magic lantern glass slides frequently present significant conservation problems, mainly due to the painting's deterioration and detachment from the glass support surface. However, the study of these objects is a very recent field. This work reviews the materials and techniques applied to hand-painted slides until the nineteenth century in Europe and North America to follow their evolution throughout time and place, aiming to further our understanding of the slides’ historical, cultural, and artistic impact. This review identifies 22 historical sources from five countries, written between the eighteenth and nineteenth centuries, containing information on the production of hand-painted slides, from the glass support to the painting materials and techniques. The production processes changed from the mid-seventeenth to the eighteenth century with the apparent transition from fired paints (enamels) to cold paints (watercolours, oil colours, and varnish colours). Different stages of eighteenth- and nineteenth-century production processes are explored. Concerning the glass support, crown and plate or ground-polished glass (later patent plate) were commonly advised. Although the paintings’ palette was mainly restricted to transparent colours, around 70 colourants and 25 binding medium components are listed. Their chronological distribution unveiled a possible correlation between their evolution and the advent of the Industrial Revolution. The knowledge of the original materials and techniques will not only contribute to understanding the differences between locations, periods, and slides’ producers, helping in future attributions, but will also support further investigations on the key factors and mechanisms that lead to the degradation of historical hand-painted slides, enabling the improvement of current conservation practices.

2024Recensão

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Lanterna Magica - Technology and Preservation of Painted Glass Slides for Projection with Magic Lanterns

Publication . Santos, Ângela Barros; Vilarigues, Márcia; Otero, Vanessa

Magic lantern is the term, deriving from the Latin lanterna magica, used to designate an early form of a slide projector in which transparent positive images depicted on glass slides (magic lantern slides) were projected onto a white surface such as a wall or screen. The invention of this apparatus in the mid-17th century allowed, for the first time, the projection of illuminated and magnified images to be viewed by collective audiences. The materials and methods applied to produce painted magic lantern glass slides and specific conservation strategies remain an understudied field. As a result, their severe deterioration problems represent an aggravated challenge for conservation professionals. The present work was developed as the first systematic study on the materials and techniques used to produce painted magic lantern glass slides (entirely painted and coloured over printed outlines), bridging the gap between 18th- and 19th-century written and material sources while addressing preventive conservation and restoration challenges. A literature review of 18th- and 19th-century written sources stating the materials and techniques applied in the magic lantern slide production was conducted, allowing for an overview of the types of glass support procured and the colour palette and binders available. The evolution of magic lantern instruments and illumination systems is also explored. Formulations of Winsor & Newton watercolours were investigated, revealing great complexity and individuality depending on the colourant used in each formulation. The context of the use and impact of the magic lanterns in Portugal throughout time was briefly investigated, and two Portuguese collections of magic lantern slides held by the Portuguese Cinematheque – Museum of Cinema (CPMC) and the National Museum of Natural History and Science (MUHNAC) of the University of Lisbon were selected for the present study. These collections’ characteristics are discussed, and the glass support and painting materials used in 48 of their slides, attributed to a European production of the 18th and 19th centuries, were studied by resorting to a multi-analytical approach. The techniques of Energy Dispersive X-Ray Fluorescence spectrometry (EDXRF), Ultraviolet- Visible (UV-VIS) and Raman spectroscopies were applied in situ, and Fourier Transformed Infrared spectroscopy (FTIR) and Surface-enhanced Raman Spectroscopy (SERS) were carried out on micro-samples. EDXRF allied with semi-quantitative analysis by WinAxil program (making use of glass standards from Corning Museum of Glass (Corning, NY, USA) for validation) allowed the identification of four main glass compositional groups: potassium-rich, mixed-alkali, high-lime low-alkali, and synthetic soda-rich glass. These results, along with visual analysis, verified the preference for high-quality glass reported by historical documentation, and the characteristics of each compositional group helped in the slides’ attributions to certain regions and periods of production. By complementing EDXRF with UV-VIS, Raman, and FTIR spectroscopy, it was possible to identify several colourants, including yellow ochre, gamboge, red ochre, cochineal-based lakes, geranium lakes, vermilion, Prussian blue, ultramarine blue, copper-green, and carbon black, and fillers such as gypsum. Regarding these paints’ binding components, FTIR detected terpenoid resins, namely mastic and shellac and the possible presence of oils. Finally, the SERS technique enabled the identification of carminic acid in a reddish micro-sample. These analyses verified the use of a reduced colour palette, the artist’s preference for bright and pure colours, and simple mixtures to create different hues and gradients. This material characterisation unveiled a strong correlation between the glass and painting materials identified in 18th- and 19th-century slides and those described by coeval written sources and enabled the development of a timeline comprising the evolution of glass procured and the colour palette used in the production of painted slides. It was also possible to find differences between manufacturers, countries, and periods, which may help attribute slides more precisely. Finally, the conservation challenges faced by caretakers and conservation professionals were addressed. The state of preservation of more than 350 slides of interest from the Portuguese collections studied was assessed, and the most common damages were identified, some of them resorting to Optical Microscopy. This study demonstrated that the glass and the painting layers are the most fragile and damaged materials that compose these slides. Considering the material knowledge gathered and inputs from national and international institutions shared through a questionnaire, preventive conservation guidelines tailored to painted slide collections were developed to complement current conservation standards. As around 20 % of the slides studied are in poor or very poor conditions and need remedial or restoration actions, and no guidelines for these procedures on painted magic lantern slides were found by the author, this study also explored methods for cleaning painted surfaces and reassembling their glass support. However, a deep investigation regarding consolidation materials and methods for these transparent painting layers is fundamental. This interdisciplinary research offers a valuable contribution to the understanding of painted magic lantern slides, aiming at increasing awareness and appreciation for these collections to ensure their long-term preservation and fruition by present and future generations.

2024Tese de doutoramento

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Fundação para a Ciência e a Tecnologia

Número da atribuição

COVID/BD/152617/2022