Testing Aquazol®. An Evaluation of its Suitability for the Conservation of Works on Paper

ABSTRACT

Aquazol® has several qualities that make it an interesting conservation material, but there are also some concerns, especially regarding its hygroscopicity and possible discolouration. Focussing on its use as a non-aqueous adhesive, this study investigates the interaction between the synthetic resin and paper to evaluate its suitability for paper conservation. Out of a variety of solvents, acetone and MEK were chosen to prepare Aquazol® solutions applied to various paper substrates. Testing included spectrophotometry, tensile strength and pH measurements before and after accelerated aging, and an assessment of reversibility and moisture uptake with the associated stickiness of the adhesive films. While there is no evidence that Aquazol® negatively affects the mechanical stability or pH of paper, a tendency towards yellowing and darkening was confirmed. Its hygroscopicity can become an issue in a non-controlled environment.

ZUSAMMENFASSUNG

Verschiedene Eigenschaften machen Aquazol® zu einem interessanten Bindemittel für die Restaurierung. Vor allem in der Papierrestaurierung gibt es jedoch Bedeneken, da es ein sehr hygroskopisches Material ist und mit Vergilbung assoziiert wird. In dieser Testreihe wurden die Wechselwirkungen zwischen Aquazol® und verschiedenen Papiersorten untersucht, um seine Eignung für die Restaurierung von Papierobjekten zu überprüfen. Der Fokus lag dabei auf der Verwendung als wasserfreie Lösung. Als Untersuchungsmethoden kamen Spektralfotometrie, Zugprüftests und pH-Messungen vor und nach künstlicher Alterung zum Einsatz. Außerdem wurden die Reversibilität und die Feuchtigkeitsaufnahme und damit einhergehende Klebrigkeit der aufgetragenen Filme überprüft. Es konnte keine Beeinträchtigung der mechanischen Stabilität oder des pH-Werts der Papiere durch Aquazol® festgestellt werden, eine Tendenz zum Vergilben und Nachdunklen wurde jedoch bestätigt. In einer nicht klimatisierten Umgebung kann die Hygroskopizität problematisch werden.

KEYWORDS:

• Aquazol®
• non-aqueous adhesive
• synthetic resin
• yellowing
• material testing
• accelerated ageing

SCHLAGWÖRTER:

• Aquazol®
• wasserfreie Bindemittel
• Kunstharz
• Werkstoffprüfung
• Farbveränderung
• künstliche Alterung

Acknowledgements

This study started as part of an Andrew W. Mellon fellowship at the Sherman Fairchild Center for Works on Paper and Photographic Conservation at the Metropolitan Museum of Art, New York. I would like to thank my fellowship supervisor Rachel Mustalish for her guidance and support.

Furthermore, I would like to thank Katie Sanderson (Metropolitan Museum of Art, Photograph Conservation), Julie Arslanoglu (Metropolitan Museum of Art, Scientific Research), Hannah Flock (CICS Cologne Institute of Conservation Sciences), Annika Dix (Germanisches Nationalmuseum) and Daniel Wheeldon (University of Edinburgh).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Aquazol® Type 50, 200 and 500 relate to the molecular weight of 50.000, 200.000 and 500.000.

2 Aquazol® 200, 20% (w/v) solutions in ethanol, methanol, butanone (aka methyl ethyl ketone), acetone, methylene chloride; Aquazol® 200, 2% (w/v) solutions in toluene, pentane.

3 Aquazol® films are reported to reach stable mechanical conditions after seven days (Wolbers et al., 1998; Arslanoglu and Tallent, 2003).

4 After finishing the experimental phase, another study on thermal ageing of heat- and solvent-set tissues was published in 2022 (pre-published online in 2020), including Aquazol® as an adhesive (see Kelly et al., 2022).

5 As defined by ASTM D 6819-02, samples should be aged at 100°C for 120 h. According to Bégin and Kaminska (Bégin and Kaminska, 2002), 90°C for 336 h is an acceptable modification. Due to the maximum temperature of the available oven, the procedure was modified further to 85°C for 336 h.

6 The measurements were taken with an Xrite eXact Advanced Spectrophotometer, set at a D65 standard illuminant and 2° standard observer. The aperture was 4mm. Positioning the device at the same location before and after ageing was ensured by using a template made from polyester film. Five readings were taken and averaged for each spot. The device was lifted and repositioned in between the readings. Standard deviation was not recorded. A specified by the manufacturer it amounts to 0.05 ΔEab.

7 A positive Δb* marks a shift to yellow, a negative Δb* a shift to blue.

8 A positive Δa* marks a shift to red, a negative Δa* a shift to green.

9 It was not possible to do this experiment inside the humidity chamber. Each sample was taken out into room conditions of 50% RH and 22°C, and the test was performed immediately.

10 See Nelson et al., 1982.

Additional information

Notes on contributors

Johanna Ziegler

Johanna Ziegler received her master’s degree in Conservation and Restoration of Art and Cultural Property from the Cologne Institute of Conservation Sciences in 2013. Until 2015, she worked as a paper conservator at the Germanisches Nationalmuseum in Nürnberg. From 2015 to 2016 she completed an Andrew W. Mellon Fellowship at the Sherman Fairchild Centre for Works on Paper and Photographic Conservation at the Metropolitan Museum of Art, New York. Her research into Aquazol® started as part of this fellowship. In 2017, she began her current occupation in the conservation department of the Kupferstich-Kabinett Dresden.