Surface treatment of acrylic sheet: evaluating cleaning and polishing commercial products as used by Lourdes Castro

Sara Babo, Joana Lia Ferreira, Ana Maria Ramos and Maria João Melo

Universidade NOVA de Lisboa, Portugal

In this work, commercial products for cleaning and polishing poly(methyl methacrylate), PMMA, have been assessed following the procedure used by one of the most important Portuguese artists working with this material, Lourdes Castro (b. 1930).
The artist worked with acrylic sheet from 1964 until 1968 to produce her “projected shadows”. She was attracted by the “immateriality” of this new material and explored its transparency and lightness to create objects that result from the superposition of several planes, through which the light is transmitted and ultimately projected on the wall as a shadow. Thus, pristine surfaces are fundamental for these artworks.
Despite PMMA recognized chemical stability, acrylic objects pose considerable challenges regarding their conservation. A simple procedure such as cleaning may be problematic and methodologies to assess the safety of different procedures have been developed during the last decade. Research has been focused on finding the most efficient and safe methods for conservators. In this work, a different goal has been followed. We focused on commercial cleaning and polishing products from Altuglas as used by Lourdes Castro. She applied these products as a final treatment for her PMMA artworks, has continued to use it as a maintenance procedure, and still recommends it every time her works are displayed. As these products have been commercialized by one of the main producers of acrylic sheet, it can be assumed that they have probably been used by other artists or art collectors. However, these ready-to-use products may have been developed without the same concerns conservators have, and therefore need to be tested in relation to their long term impact on artworks. In this work, the safety of the Altuglas products has been tested and compared with the use of distilled water + non ionic detergent, as recommended for plastic artefacts in museum collections. Different types of PMMA sheets were used as testing samples: transparent/opaque; new/from 1960s; plane/thermoformed.The accumulation effect of cleaning and polishing actions in an artwork during its life was reproduced by submitting the samples to several cycles of cleaning and/orpolishing followed by artificial ageing in a solarbox, in a total of 12 cycles during 4000h. Samples were periodically characterized by gravimetry, UV-visible and infrared spectroscopies, size exclusion chromatography, micro-indentation, colorimetry, and optical microscopy.
Assessing the influence that these procedures may have in the long-term stability of PMMA will help to understand the current condition of artworks, to decide how they should be cleaned in the future, and to inform artists and conservators about the safety of these products.