Original articleResponse surfaces model for restoring and cleaning oil painted artworks
Introduction
In the field of restoration, cleaning can be defined as any activity aimed at removing external surface layers (surface dirt or aged varnishes) that are not part of the artwork's original composition and which make it difficult to see the original surface, or which affect its integrity.
Although procedures for cleaning works of art have been used since antiquity, it was only in the second half of the 20th century when scientific study began to use organic solvents provided by industry with different properties and variable levels of toxicity, most notably in the classic studies by Hildebrand & Scott, Teas, Feller and Hansen [1], [2], [3], [4], [5].
The work by Masschelein-Kleiner [6] stands out in the sphere of restoration. It related the effectiveness of the treatment to the type of dirt, the characteristics of the picture's surface and the type and condition of the varnishes protecting it. Since the end of the 1980s, different water-based cleaning systems with low toxicity have been developed in order to improve on the results from traditional organic solvents and to reduce the risks for the restorers. Different researchers have put forward formulations that combine solvents, surfactants, chelating agents, enzymes, buffer solutions and gellants, seeking to be selective in the removal of undesired matter with as little damage as possible to the original artwork [7], [8], [9], [10], [11], [12], [13], [14], [15], [16].
It is in this context that we are proposing formulations to clean polychrome artworks using mixtures of water and limonene, stabilized with non-ionic surfactants. Limonene (1-Methyl-4-(1-methylethenyl)-cyclohexene) is a colorless liquid hydrocarbon classified as a cyclic monoterpene. It is chiefly produced from a natural source: citrus oil, as a by-product of orange juice manufacture. Limonene is a chiral molecule, and biological sources produce one enantiomer: d-limonene, which is the R-enantiomer (CAS number 5989-27-5). The enantiomer d-Limonene is a chemical with low toxicity based upon lethal dose (LD50 Oral=5.600 mg/kg in male mice and 4.400 mg/kg in male rats) [17]. There is no evidence for carcinogenicity or genotoxicity in humans and it is not deemed necessary to use breathing protection when handling it, although limonene and its oxidation products are respiratory and skin irritants if exposed to the pure compound for a long time or if it is ingested [17], [18]. Applied in common polychrome restoration techniques, it may be considered a low-toxic, much safer product to use than most other classic solvents normally employed in this field. However, in the field of restoration of cultural assets, it is not a product that is often used. Indeed, this study is the first to evaluate the use of limonene compositions to clean and remove natural varnish in professional restoration techniques forpolychrome painted artworks.
Section snippets
Research aim
The purpose of this study is to test the aforementioned cleaning formulations using a statistical design for experiments via the MODDE GO® program in order to obtain a response surfaces model. The pigments, types of varnish and extent of aging are varied in order to optimize the complex process of cleaning oil paintings. We seek to evaluate the statistical validity of the model and determine the main factors that influence the process for cleaning works of art painted with oil. This model is
Response surfaces model
The response surface methodology is traditionally used to model complex systems with numerous factors and responses in engineering and development of cleaning product formulations, and even in social sciences to evaluate scientific activity, considered as a complex system [19], [20], [21]. The proposed model considers the cleaning of polychrome painted artworks to be a procedure affected by a set of values or variables that is evaluated via a set of responses. The factors can be quantitative or
Validity of the model
In order to confirm the validity of the model, the predicted values for the model were compared with the values observed experimentally for each response. The absolute and relative errors were also calculated, correlating the latter with the experiments’ order of implementation (run) so as to discard any bias related to the way and order in which they were implemented. Equally, they were correlated with the value of each response, either in their observed values or in their predicted values, so
Conclusions
A response surfaces model has been proposed for cleaning oil paintings with aqueous-based and limonene cleaning formulas using the MODDE GO®program, and its statistical validity has been demonstrated.
The main factors that influence cleaning with the proposed formulations were the concentrations of water and limonene as the main solvents and which regulate the cleaners’ level of hydrophilia and lipophilicity, followed by the type of varnish, aging and types of pigments. The other components in
Acknowledgements
This study was supported by the National Spanish Project “I+D” reference: HAR2016-79886-P.
References (29)
- et al.
New simple procedure to produce white lead for special use in the plastic arts and in restoration
J. Cult. Herit.
(2017) - et al.
Regular Solutions
(1962) Graphic analysis of resin solubilities
J. Paint Technol.
(1968)- et al.
On Picture Varnishes and Their Solvents
(1985) The three dimensional solubility parameter – key to paint component affinities: I. solvents, plasticizers, polymers, and resins
J. Paint Technol.
(1967)Hansen Solubility Parameters: A user's handbook
(2007)Liants, Vernis et Adhésifs Anciens
(1992)Solvents properties, materials for conservation: organic consolidants, adhesives and coatings
Butterworths
(1987)A survey of the conservation literature relating to the development of aqueous gel cleaning on painting and varnished surfaces
Rev. Conserv. IIC
(2000)Cleaning painted surfaces: aqueous methods
Stud. Conserv.
(2001)
Cleaning painted surfaces: evaluation of leaching phenomenon induced by solvents applied for the removal of gel residues
Environ. Sci. Pollut. Res.
L’uso Dei Solvent Organic Nella Pulitura di Opera Policrome
L’ambiente Acquoso per la Pulitura di Opere Policrome
Cleaning Painted Surfaces: Aqueous Methods
Cited by (1)
Isosorbide, pyrogallol, and limonene-containing thiol-ene photocured bio-based organogels for the cleaning of artworks
2022, Journal of Cultural HeritageCitation Excerpt :The cleaning process of historical artworks for conservation and restoration purposes includes the removal of dirt, grime, stains, and soil as well as the removal of degraded layers such as aged, yellowed varnishes, and coatings [1,2]. Even though it has been performed since antiquity, modern, systematic and scientific approaches began to appear towards the end of the 20th century [2,3]. The traditional method is to clean the surface of paintings by using pure solvents or solvent mixtures and applying them directly on the coating layers or paintings with the aid of cotton swabs or brushes [4].