The role of agar gel in treating water stains on acrylic paintings: Case study of Composition, 1963 by Justin Knowles

ABSTRACT

This paper describes the historic context and explains the treatment rationale for minimizing disfiguring water stains on a large-scale, acrylic dispersion canvas painting: Composition, 1963, by British artist Justin Knowles. Composition is a brightly colored, hard-line geometric abstraction juxtaposed against an unpigmented acrylic dispersion-sized linen canvas. Accidental water damage produced tidal stains across the sized canvas, rendering it unexhibitable. Investigations into the relationship between materials and meaning in Knowles’ work, alongside literature on the cleaning of acrylic dispersion paintings, textiles, and works on paper facilitated the development of a tailored cleaning treatment involving the use of agar gel as an aqueous delivery system, which minimized risk to the painting materials, whilst facilitating a satisfactory reduction and subsequent visual integration of the water stain. As a final stage, a number of retouching media commonly used on acrylic paints were evaluated, and a successful method was determined using Aquazol 50 and dry pigments. The success of retouching was also evaluated via visual assessment, highlight-based RTI, and digital microscopy (HIROX). As a result of this collaborative approach, this important work has been successfully returned to displayable condition.

RÉSUMÉ

Cet article décrit le contexte historique et explique les raisons menant aux choix de traitement visant à atténuer les cernes d’eau qui nuisent à la lisibilité de Composition, 1963, une œuvre sur toile de grandes dimensions de l’artiste britannique Justin Knowles.Il s’agit d’une œuvre exécutée à la peinture acrylique en dispersion représentant une abstraction géométrique faite de traits contrastants et de couleurs vives juxtaposée contre une toile de lin recouverte d’une couche d’encollage à base de dispersion acrylique non pigmentée. Des cernes d’eau apparurent à travers la toile à la suite d’un dégât d’eau accidentel, ce qui empêche la mise en valeur de l’œuvre en exposition. L’étude de la relation entre les matériaux utilisés dans les œuvres de Knowles et la signification de ces œuvres, de même qu’une recherche de la littérature concernant le nettoyage de couches picturales faites de dispersions acryliques sur des peintures, des textiles et des œuvres sur papier permirent le développement d’un traitement de nettoyage ciblé mettant à profit l’utilisation d’un gel d’agar-agar en tant que système d’apport d’eau. Cette approche permit de minimiser les risques que pouvaient encourir les matériaux dont était faite l’œuvre au cours du traitement tout en permettant un niveau satisfaisant d’atténuation visuelle des cernes suivi de leur intégration visuelle. En dernière étape, plusieurs types de liants couramment utilisés pour la retouche des peintures acryliques furent évalués et une méthode fut développée à l’aide d’Aquazol et de pigments secs qui donna de bons résultats, tels qu’évalués visuellement ainsi qu’à l’aide d’imagerie de transformation de la réflectance basée sur la détection du reflet spéculaire (highlight-based Reflectance Transformation Imaging (RTI) ) et par microscopie numérique (HIROX). Le résultat de cette approche collaborative fut l’amélioration de l’état de cette œuvre importante, permettant ainsi sa mise en valeur en exposition. Traduit par Carole Dignard et Marie-Hélène Nadeau.

RESUMO

Este artigo descreve o contexto histórico e explica a lógica do tratamento para minimizar em larga escala manchas d’água desfigurantes em uma tela com dispersão acrílica: Composition, 1963, do artista britânico Justin Knowles. A composição é uma abstração geométrica de linhas duras, colorida e brilhante justaposta a uma tela de linho com dispersão acrílica não pigmentada. Danos acidentais causados ⁣⁣pela água produziram manchas em toda a tela, tornando-a impossivel de exibir. Pesquisas feitas sobre a relação entre materiais e significado no trabalho de Knowles, juntamente com a literatura sobre a limpeza de pinturas em acrílico, têxteis e trabalhos em papel facilitaram o desenvolvimento de um tratamento de limpeza sob medida; envolvendo o uso de gel agar como um sistema aquoso, o que minimizou o risco para os materiais da pintura, enquanto facilitou uma redução satisfatória e posterior integração visual da mancha d’água. Como um estágio final, vários meios de retoque comumente usados ⁣⁣em tintas acrílicas foram avaliados, e um método bem sucedido foi determinado usando Aquazol 50 e pigmentos secos. O sucesso do retoque também foi avaliado por meio de avaliação visual, RTI e microscopia digital (HIROX). Como resultado dessa abordagem colaborativa, esse importante trabalho voltou, com sucesso, a ter condição para exibição. Traduzido por Beatriz Haspo.

RESUMEN

Este trabajo describe el contexto histórico y da argumentos sobre el tratamiento utilizado para minimizar manchas de agua desfigurantes en una pintura de dispersión acrílica a gran escala: Composition, 1963, del artista Británico Justin Knowles. Composition es una abstracción geométrica de líneas duras y colores brillantes yuxtapuesta sobre un lienzo cubierto con una dispersión de acrílico sin pigmento. Un daño accidental produjo manchas de arrastre de agua de un lado al otro del lienzo transformándolo en no-exhibible. Las investigaciones sobre la relación entre los materiales y el significado del trabajo de Knowles, junto con literatura sobre limpieza de dispersiones acrílicas en pinturas, textiles, y obras sobre papel, facilitaron el desarrollo de un tratamiento de limpieza a medida. Este tratamiento involucra el uso de gelatina de agar como sistema de distribución, que minimiza el riesgo a los materiales pictóricos al mismo tiempo que facilita una reducción satisfactoria de la mancha de agua e integración visual subsecuente. Como etapa final, se evaluaron un numero de medios de retoque utilizados comúnmente en pinturas acrílicas, y se determinó un método exitoso utilizando Aquazol 50 y pigmentos secos. El éxito del retoque se evaluó mediante observación visual, reflejos basados en imágenes de transformación de reflectancia, y microscopia digital (HIROX). Como resultado de este enfoque colaborativo, este trabajo tan importante ha sido devuelto a condiciones que permiten su exhibición. Traducción: María Esteva, revisión: Amparo Rueda.

KEYWORDS:

• Water stained canvas
• Justin Knowles
• sized canvas
• acrylic emulsion
• unpigmented acrylic paint
• tide lines
• surfactant
• agarose gel

Acknowledgements

Hirox 3D digital microscopy was carried out at Tate Britain, London, the purchase of which was supported in part by the Horizon2020 funded NanoRestArt project (agreement 64603). In addition, FTIR-ATR was carried out at Tate, with training and assistance from Dr Bronwyn Ormsby. AFM was carried out at Kings College London with training and assistance from William Luckhurst. RTI was supervised and aided in the Courtauld Institute of Art Photograph Studio by Elizabeth Keats Webb from the Smithsonian Museum Conservation Institute, Washington, DC. Richard Wolbers from the University of Delaware was very insightful regarding the reasoning for lower conductivity values measured from the unpigmented acrylic dispersion size layer.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Olympia Diamond is a paintings conservator at Julia Nagle Conservation, London, UK. Prior to joining JNC in 2017 she was Assistant Paintings Conservator at National Museums Liverpool, where she led the Art Fund supported conservation treatment and technical investigation of the Bartolome Esteban Murillo (1617–1682) altarpiece, Virgin and Child in Glory, c 1673 and its related oil sketch. She completed the Postgraduate Diploma in the Conservation of Easel Paintings at The Courtauld Institute of Art in 2014 and has worked for the Guildhall Art Gallery and English Heritage. Address: Julia Nagle Conservation, Neville Place, London, N22 8HX, UK. Email: [email protected].

Maggie Barkovic is assistant paintings conservator at the Williamstown Art Conservation Center in Williamstown, MA. She has completed internships at the Barnes Foundation, the Phillips Collection, the Smithsonian Museum Conservation Institute, TU Delft, and Atelier Marjan de Visser. She has a Postgraduate Diploma from the Conservation of Easel Paintings at The Courtauld Institute of Art (2016), an MA in Art History from George Mason University (2012), and a BA in Chemistry from Virginia Tech (2008). Address: WACC, 25 South St, Williamstown, MA 01267, USA. Email: [email protected].

Maureen Cross has held a position as a full-time lecturer in the Department of Conservation & Technology at the Courtauld Institute of Art since 2005. Before joining the Courtauld, Maureen worked as a professional conservator at the National Museums and Galleries on Merseyside, the Manchester Galleries, and Tate. Additionally, she has worked in both the curatorial and conservation departments of the Brooklyn Museum of Art and was an Andrew W. Mellon Fellow in the Antonio Ratti Textile Center Storage at the Metropolitan Museum of Art. Maureen has a MA (Dist) in the conservation of easel paintings from the University of Northumbria (1998). Address: Conservation and Technology Department, Courtauld Institute of Art, Somerset House, Strand, London, WC2R 0RN, UK. Email: [email protected].

Bronwyn Ormsby is Principal Conservation Scientist at Tate and has extensive research and analytical experience of modern paints and research into the cleaning of modern and contemporary painted art. Address: Tate Britain, Conservation Department, Millbank, Pimlico, London, SW1P 4RG, UK. Email: [email protected].

Sources of materials

Agar gel, Boric acid, sodium borohydride, DPTA, triethanolamine, triammonium citrate

Sigma-Aldrich Ltd.

Second Avenue

Heatherhouse Industrial Estate

Irvine KA12 8NB, UK

http://www.sigmaaldrich.com/united-kingdom.html

Linen canvas

Russell & Chapple

30-31 Store St.

Bloomsbury

London WC1E 7QE, UK

https://www.russellandchapple.co.uk/

ECOSURF EH9

The Dow Chemical Company

Diamond House Lotus Park

The Causeway

Staines TW18 3AG, UK

http://campusemeai.dow.com/en-us/locations/united-kingdom

Mitka suction disk

MITKA & Partners

Kronprinsessegade 58A, st

DK-1306 Copenhagen K, Denmark

Phone: [phone]

http://www.mitka.dk/

Notes

1 The test canvas replicas were then submerged in water to recreate the dark tide-lines. XRF analysis detected peaks for iron and calcium and the water stain mixture was created using in 2000 ml of tap water, 14 rusty nails, 4 pieces of deteriorated linen, 2 pieces of non-deteriorated linen, 4.20 g of saw dust, 2 drops of ECOSURF EH 6 non-ionic surfactant and dirt and dust. The mixture was based on discussions with Stephen Hackney (formerly TATE), Mark van Gelder, conservator, and Jay Krueger, National Gallery Washington (Diamond 2014) The test canvases were then aged in a light box at TATE. The temperature in the light box was ∼ 28°C with a 22% RH and the UV was filtered out from the light bulbs. Assuming reciprocity of exposure at 200 lux for 10 h a day for 730 days (2 years) with an average lux in light box of 7,980 lux resulted in 183 h exposure in the light box. Although the RH and temperature were not equivalent to museum conditions, the light levels were able to be calculated, assuming reciprocity.

2 These readings were taken by applying agar pellets (2.5% w/v, 1 cm diameter, 2 mm thick) to the surface for one minute, and measuring the pH and conductivity with an OmegaPHH-7200 meter. This was repeated three times for each testing area. An average pH and conductivity were measured for each test canvas and for Composition; this was used to determine the isotonic range for cleaning tests.

3 The cleaning solutions trailed were made separately, mixed with agar powder, heated, and then formed a gel which was traced and cut to fit the stain—the amount of agar powder used (i.e. the % weight content) added impacted the pore size of the gel, changing its rigidity (Cremonesi 2010; Cremonesi and Casoli 2017) and the rate at which it transfuses water. The rate of diffusion by agarose gel has not been studied; however, practically it is based on the concentration of agar and the isotonicity of the cleaning solution with the painting. Based on the principles of osmosis, a larger difference in pH and conductivity between the agarose gel and the painting may promote a faster rate. A lower concentration of agar in the gel will result in a higher water content which will also speed up the rate of diffusion into the paint film.

Additional information

Funding

Hirox 3D digital microscopy was carried out at Tate Britain, London, the purchase of which was supported in part by the Horizon2020 funded NanoRestArt project (agreement 64603).