The Portuguese artist Ângelo de Sousa (1938-2011) produced noteworthy work in photography
and experimental film. However, a lack of in-depth studies focusing on the use of these media by the
artist is acknowledged. Thus, his work has been studied, particularly through unpublished
documentation found in the artist’s house and in public archives, bringing new insights into his
production. Despite the delay in the artistic context felt in Portugal in the post-modern period, Ângelo
de Sousa produce photographic and film work perfectly in line with that of other international artists.
The slide-based artwork Slides de Cavalete (1978-1979), constructed with the additive synthesis of
colours, stands out as an example of the inventiveness achieved by the artist with these media. The
production process behind Slides de Cavalete has been studied and reproduced, allowing for a thorough
understanding of the work and contributing to the definition of its significance.
The photographs and films have been gathered together in his house. Since typologies,
quantities and condition of the materials were unknown, a survey was carried out to enhance
knowledge of the collection and to define preservation priorities. Accordingly, 35 mm chromogenic
reversal films (slides), used to produce almost all his photographic colour work, was highlighted as the
set in highest risk due to colour change detected in one third of these materials. Thereby, slide-based
artworks by Ângelo de Sousa were studied in further detail.
The display options undertaken by the artist during his lifetime have been investigated, in order
to guide the decision-making process regarding the exhibition and preservation of his slide-based
artworks. Slides de Cavalete was selected as a case study, and the history of its exhibition was assessed
by searching for documentation and interviewing people. Thus, it is understood that the work was first
presented projected on a canvas over an easel, in 1979. Since the artist’s death, the work has been
presented without this setup, and recently, as a digital projection. An exhibition was conducted at FCT
NOVA, to test the variability of the work displayed with a digital and a slide projector. Based on a
questionnaire, a clear preference for the slide projection was acknowledged. Thus, guidelines for the
exhibition of Slides de Cavalete are defined, following its first presentation.
Considering that chromogenic reversal films are highly susceptible to colour change and that
there is still much to know about these materials, their molecular characterization and degradation has
been studied. Different pathways to characterize chromogenic dyes are suggested based on
chromatographic and spectroscopic techniques. Additionally, a methodology to accurately monitor
colour change in these materials has been defined, based on samples artificially aged at different
temperatures (50, 60, 70 and 80˚C) and relative humidity (40% and 60%). The samples were assessed
using spectrophotometry with optical fibre probes in the ultraviolet-visible range. From the spectral
data, intensity maximums, CIE L*a*b* coordinates and the total colour variation (ΔE*) have been
determined. Optical microscopy and digitization have also proven useful for degradation assessment on
these materials
