New Insights into the Cleaning of Paintings

Effects of Commercial Soaps
on Unvarnished Painted Surfaces:
A Pilot Study for Their Assessment
Andrés Sánchez- Ledesma, Carmen Muro- García,
and María Dolores Gayo- García
Abstract. The elimination of soiling from painted surfaces, especially for recent unvarnished
paintings, by means of alkaline soaps with a high pH poses a significant risk to the objects. The
wide range of objects that can be treated with these products and their long- standing presence on
the specialist market have led to this pilot study to evaluate the existence of residues and/or damage
from them on painted surfaces. The methodology applied involves the use of analytical techniques
such as gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, polarized
light microscopy, scanning electron microscopy and energy- dispersive X- ray spectroscopy, and
confocal scanning microscopy. This study presents the results from the use of Vulpex soap at low
concentrations in an aqueous solution, in white spirit, and in fluid hydroxypropyl cellulose gels, applied
directly on the unvarnished painting or on barrier paper and rigid agar gels. A reduction in the
amount of residues was observed when soap was used in a 1% concentration in white spirit or as a
gel. All the aqueous treatments caused surface damage, especially cracking, flattening, and particle
removal and accumulation. The damage may be associated with both the application method and
the rinsing process. Some treatments have been tested by a team of professional restorers, and a
good correspondence was found with the results from the test samples. The main difference between
restorers appears to depend on the area of the painting that was treated.
INTRODUCTION
Andrés Sánchez-Ledesma, Museo Thyssen Bornemisza,
Paseo del Prado 8, 28014 Madrid, Spain.
Carmen Muro-García, Museo Nacional Centro
de Arte Reina Sofía, Calle Santa Isabel 52, 28012
Madrid, Spain. María Dolores Gayo- García,
Museo Nacional del Prado, Calle Ruiz de Alarcón
23, 28014 Madrid, Spain. Correspondence: Andrés
Sánchez- Ledesma, asanchezledesma@artelab.es;
Carmen Muro- García, carmen.muro@
mcu.es; María Dolores Gayo- García, dolores.
gayo@museodelprado.es. Manuscript received 19
November 2010; accepted 24 August 2012.
The wide range of pictorial techniques and finishes employed in paintings held at
the Museo Thyssen- Bornemisza, Museo Nacional Reina Sofía, and Museo Nacional del
Prado has prompted the need for a far- reaching study of commercial products recommended
for the cleaning of paintings and sculptures. This project received the support
of several companies specializing in the distribution of restoration materials, which will
later publish the results from this pilot study. Because of the large number of restorers
who will have access to the results of these studies through these companies, the project
also included products that are not in widespread use in museum cleaning protocols but
that may present a high risk for restoration processes in general.
The first aim of the project was to develop an analysis methodology that allowed
assessment of potential damaging effects on the pictorial surface by the commercial products
and to monitor the residues after cleaning. Within the Spanish market there are several
recommended commercial cleaning products, including alkaline soaps, resin soaps,
and products formed by a complex mixture of surfactants and other additives, such as
Vulpex, resin soap 1194, resin soap 1295, Contrad 2000, and “concentrado aniónico.”