Getting old or maturing gracefully?How will the modern materials of the Pregnant woman age under standard museum conditions?

The long-term effects of light exposure on the Pregnant woman were investigated in the Conservation Department of the National Gallery of Australia, through a series of accelerated light and UV ageing tests. In the museum environment, photodegradation will be the primary mechanism of degradation of polymers used for making the sculpture. Structural changes in the different resins can adversely affect the appearance of the work of art through changes to the colour and surface texture. In Mueck’s Pregnant woman the ageing of the resins is of crucial importance, as the face and body are constructed from different base resins that have different surface finishes. The experiments conducted to assess the potential colour changes of individual resins were aimed at predicting changes in the appearance of the sculpture during its display life.

Preliminary studies on ageing characteristics of materials used in Ron Mueck’s Pregnant woman at the National Gallery of Australia.

Material girlRon Mueck’s larger than life sculpture of a pregnant woman was constructed using synthetic resins and a variety of pigments, coatings and paints. The head and the body were fabricated from different base materials.

Skin deepThe surface of the sculpture was coated with synthetic coatings and paints to imitate human skin. Acrylic wig hair was used for the eyebrows and hair.

A range of materials were used as the surface finish on the face and the body: polyester pigments; artist’s picture varnish for oil, alkyd and acrylic (in satin, matt or gloss) by Winsor & Newton; soluble matt varnish for acrylics by Daler Rowney; acrylic media (matt, satin, gloss) by Lascaux, Vallejo, Daler Rowney; medium viscosity artist colours by Liquitex and Acrilico Studio von Vallejo; silicone pigments, universal stainer for silicone; Sunsilk hairspray.

Beyond appearances: the testing procedureUnmodified samples of the resins, varnishes and acrylic media, known to have been used by the artist to make the Pregnant woman, were individually applied to glass slides or cast in sheet form. Pigments and stainers were not tested. Both light and UV ageing of the samples, tested in triplicate, were carried out in eight stages, corresponding to the exposure times needed to fade Blue wool standards under the same experimental conditions. Colorimetry was used to measure colour changes induced in the resins due to light and UV ageing.

Beautiful forever?The light and UV ageing experiments indicate that photodegradation will affect several of the resins used in Mueck’s Pregnant woman. However, the results of the tests cannot be used to predict the exact time frame in which changes will occur. Although the sculpture is displayed under optimum museum conditions (no UV, low lux levels), it is likely that visible effects of photo-degradation will be observable in the decades to come. The differences in colour of the face and the body are likely to become increasingly distinct over time, and the surface finishes will become less natural in appearance.

Conservation treatment cannot arrest these processes, which are inherent in the nature of the synthetic resins used for this work of art. Preventive conservation measures that reduce the exposure to light can ensure that the Pregnant woman’s peaches and cream complexion and her radiant glow persist to full term.

The naked truth: the results of testingThe polyester resins used in the construction of the body, the Winsor and Newton varnishes, the Vallejo media and the Sunsilk hairspray all showed statistically significant and visible colour change as a result of the light and UV ageing experiments.

The silicone resins used to make the face showed no visible or measurable colour change under either light or UV radiation over the test period.

Construction of the body: Polyester resins Polylite 32032-00 thickened with Cabosil Polylite 440-M750 reinforced with Glass matting

Construction of the face: SiliconesSilicone Sealant A1521 (A1038)Silicone Adhesive Sealant A5500 Polyester backing

Face construction: cross-sectionBody construction: cross-section

Sunsilk Hairspray Ultra Hold for Extra Strength was used to imitate perspiration

Polyester pigments and matt acrylic varnish were used for the body

Ro

n Mueck P

regnant wom

an 2002 fibregass, resin, silicone N

ational Gallery of A

ustralia, Canb

erra Purchased

with the assistance of Tony and

Carol B

erg 2003 © R

on Mueck

Bare facts Ron Mueck Pregnant woman 2002 Medium: fibreglass, resin, silicone Dimensions: 252(h) x 78(w) x 72(d)cm Collection: National Gallery of Australia, Canberra On regular, open display

Results from Light ageing tests Results from UV ageing tests

Cathy Collins, Jaishree Srinivasan Beata Tworek-Matuszkiewicz

A collaborative project with the National Museum of Australia

References:F Herzog, Hyperrealistische Skulpturen am Beispel von Ron Mueck: Technik – Materialien – Aspekte der Konservierung und Restaurierung mit Schwerpunkt Siliconkautschuk und Glasfaserverstarkter Polyester, unpublished thesis, Staatliche Akademie der Bildenden Künste Stuttgart, 2004. RL Feller,‘Standards in the evaluation of thermoplastic resins’, in ICOM Committee for Conservation. 5th Triennial Meeting, Zagreb, 1–8 Oct. 1978. Preprints, International Council of Museums, Paris, 1978. R Heesters, H van Keulen and GT Roelofs, ‘Natural resins, artificially aged in steps’, in JA Mosk and NH Tennant (eds) Contributions to conservation: research in conservation at the Netherlands Institute for Cultural Heritage, James & James, London, 2002.

UV ageing

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