Microemulsions and Micellar Solutions for Cleaning Wall Painting Surfaces
Emiliano Carretti, Barbara Salvadon, Piero Bagliom, and Luigi Dei
This paper presents a new approach for the elimination of hydrophobic materials from the surface
of wall paintings. Nanostrctured systems wth well-characterized physicochemical properties are
proposed as an alternative to unsupported organic solvents for solubili:ing substances on porous
painted surfaces. Due to the wide range of components that can he used in their preparation, these
systems can potentially be used to remore a wide range of different types of organic materials. The
results of experiments using oil-in-water microemulsions and micellar solutions as cleaning agents
for wall paintings are given. The efficacy of these systems has been tested in several Italian
conservation workshops for the removal of various hydrophobic materials. In particular, they have
been successfully used during the conscription of the frescoes in the Loggia del Bigallo in Florence
(affected by degraded natural organic materials/, and for the removal of various synthetic organic
resins from the surface of the Filippo Lippi frescoes in the apse ot the Cappella Maggiore in Prat o
Cathedral. Furthermore, oil-in-water microemulsious have also been shown to be effective cleaning
agents tor the removal of oil- and acrylic-based paint used by vandals to deface an eighteenthcentury a secco painting in the lilla del Barone in Prato. The results are supported by detailed
photographic documentation and Fourier transform infrared (FTIR) spectra.
INTRODUCTION
Of the many problems associated with the cleaning of historic surfaces, the most significant are
related to the impact that both conservator and conservation materials have on the object to be
cleaned. Since the conservation of pictorial surfaces can often cause chromatic and structural
alterations [1], one of the future research goals in this field should be to minimize this impact
through the development of new conservation methods and materials and the improvement of those
already available. One of the biggest challenges during the cleaning of a painting is the removal of
substances that have a different chemical composition trom the original materials. In the past, many
different kinds of substances such as vinyl and acrylic polymers and copolymers. and protein-based
mixtures have been widely employed as consolidants, protectives and adhesives tor the
conservation of wall paintings. Natural materials such as proteins have a long history of use in
conservation, most notably since the second half of the nineteenth century: however, the last 50
years have been characterized by the increasing use ot acrylic and vinyl resins tor the treatment of
wall paintings and stone materials [2—5]. Ot the various synthetic polymeric substances used over
the last five decades, only acrylic copolymers, which were first introduced in the first halt ot the
1960s, are currently still employed in wall painting conservation [6—9]. Indeed, their enduring
popularity is such that in certain cases following their removal at the beginning of a conservation
intervention, these same materials arc then subsequently reapplied [5—10].
The most serious problems associated with all these polymeric materials are related to the changes
in their physicochemical stability that occur as a result of natviral aging [ll]. Thermal and
photochemical reactions [12— 14] result in depolymerization and cross-linking, which alter the
colour and physical appearance of the surface, cause mechanical stress to the paint layers, and lead
to the formation of craquelets. Furthermore, this also results in the alteration ot physicochemical
properties at the interface between the work ot art and its environment [15]. Consequently, it is very
often the case that conservation proposals for wall paintings that have been previously treated with
polymeric resins include a cleaning procedure to remove these aged substances. However, this must
be achieved without affecting the original materials of the painting. The complete removal of these
added materials is often a delicate problem due to the heterogeneous and porous nature ot the
support itself Furthermore, this is hampered by the fact that one of the main consequences of the
polymer degradation is a drastic loss of solubility [11], which makes their removal much more
difficult using conventional pure or mixed solvent systems (e.g. propanone (acetone), phenyl-
methanol (benzyl alcohols) and dimethylbenzenes (xylenes)). The principal outcome of this is that
the reversibility of previous treatments with polymers is reduced over time. An obvious course of
action would be to use pure hydrophobic organic solvents capable of solubilizing the aged
polymers. However, this approach can have the undesirable effect, typical ot the surfaces
considered, ot redistributing the polymeric residues further within the porous matrix.
A solution to this problem can be found in the use of dispersed microheterogeneous nanostructured
systems in the form of micellar solutions and microeniulsions, in which the dispersed solvent phase
is specifically tailored to solubihze the substances that are to be removed. Micellar solutions and
microeniulsions are stabilized by the spontaneous aggregation of amphiphilic molecules
(surfactants), as shown in Figure 1. The most important characteristic of surfactants is their
structure, which is comprised of two distinct parts: a hydrophilic (i.e. polar) head group, and one or
more hydrophobic alkyl chains to which it is attached. When the surfactant concentration is above a
certain yield value, termed the 'critical micelle concentration' or CMC, this peculiar characteristic
causes these molecules spontaneously to form
Figure 1 Schematic diagram showing types of aggregates formed by surfactant molecules: (A)
structure of a surfactant molecule; (B) spherical micelle; (C) reversed micelle; (D) oil-in-water
microemulsion: (E) water-in-oil microemulsion.
aggregates called micelles, the size and shape of which is a function of both their concentration and
chemical structure. A scheme ot the different types ot aggregates that are formed is given in Figure
1.
Surfactant solutions at concentrations above the CMC are termed 'micellar solutions'. The micellar
solutions used for this study are somewhat complex, in that they also comprise a co-solvent, which
is adsorbed at the micellar intertace and plays a synergistic role together with the surfactant micelles
during cleaning. Microeniulsions differ from micellar solutions due to the presence of a second
liquid component termed the dispersed phase (e.g. the oil in oil-in-water microeniulsions) that is
insoluble m the solvent, which is termed the continuous phase (e.g. the water in oil-in-water
microeniulsions). The dispersed phase forms microdrop-lets in the continuous phase, which are
stabilized by adsorption of the surfactant at the interface between the microdroplets and the solvent.
Both microeniulsions and micellar solutions are optically transparent and thermo-dynamically
stable.
The most important and innovative aspects of this approach are as follows:
• Redistribution ot the solubilized hydrophobic material into the porous matrix is avoided since
solubilization takes place within the core of the microdroplets, and/or at their interface with the continuous aqueous phase [16-17]. Thus, the aqueous dispersant medium forms a hydrophilic barrier
which prevents the polymer from penetrating further into the porous structure.
• The dispersed systems are thermodynamically stable throughout a wide range of environmental
operating conditions.
•
The environmental impact of the treatment is drastically reduced since the oil fraction (an
organic apolar solvent) ot the oil-in-water nucroemulsions is typically less than 15% by weight [1821].
The first cleaning procedure based on the use of micro-emulsions was devised in 1991 by Ferrom et
al [22], During the conservation of the Brancacci Chapel frescoes by Masaccio, Masolino and
Filippino Lippi, the conservators were faced with the problem of how to remove hydrophobic
deposits mainly composed of candle wax. To this end, the well-known system dodecane-in-water
(using sodium dodecylsulphate (SDS) as a surfactant and pentan-1-ol as a co-surfactant) was
selected. Two of its most important characteristics were the amount of the active oil phase (0.8
volume fraction) and its high efficacy for solubilizing wax, which in laboratory simulations on
marble was as much as 77% by weight [23].
The effectiveness of dispersed systems as solubilizing [20, 24-27] and extracting [28] agents, and
the wide range of components from which they can be prepared indicates that they can be used for
the removal of many organic substances such as smoke, grease, synthetic polymers, and proteins.
The dissolution mechanism is, of course, related to the kind of substance that is to be removed. The
aim of the present study is to report recent advances and results concerning the use of these
innovative nanostructured systems consisting of oil and water (o/w) microemulsions and micellar
solutions tor the surface cleaning of wall paintings.
Treatment tests using these matenals were undertaken at three different sites: the frescoes in the
Loggia del Bigallo in Florence (which are affected by degraded natural organic materials), the
Filippo Lippi frescoes in the apse of the Cappella Maggiore in Prato Cathedral (for the removal ot
various vinyl and acrylic synthetic resins), and finally for the removal of oil- and acrylic-based paint
used by vandals to deface an eighteenth-century a secco painting in the Villa del Barone m Prato.
MATERIALS AND METHODS
For the experimental work the following materials were used: p-xylene, sodium dodecylsulphate
(SDS). commercial nitro-diluent (ND), pentan-1-ol (PeOH), 4-methyl-l,3-dioxolan-2-one
(propylene carbonate.
PC), and benzyl alcohol (BA). All products were used as obtained from the supplier, without any
further purification. Two different types of water were used: HPLC-grade (resistance > 18 MΩ.cm)
obtained using a Milli-RO6 plus Milli-Q-Water (Organex) purifying system; and normal deionized
water.
The microemulsions were prepared by dispersing a given amount of pentan-1-ol (as indicated in
Table 1) in an aqueous solution containing 48g-L-1 of sodium dodecylsulphate. Following this,
pentan-1-ol was gradually added while stirring at 25°C. The system, which is initially opalescent,
suddenly becomes limpid after a few minutes. Next the dispersed phase (p-xylene and ND) was
added. For microemulsion B, the p-xylene was added first, and then the nitro-diluent. The system
was stirred continually until a macroscopically clear solution was obtained.
For the preparation of the micellar solutions given in Table 2. propylene carbonate was added to the
SDS/ PeOH/water system in the stated amounts. After its addition the solution was stirred at 25°C
for a few minutes until a clear system was obtained, and then the nitro-diluent and the benzyl
alcohol were added. The micellar solutions or o/w microemulsions were applied using an Arbocel
compress [30] according to the methodology given below.
Micro-samples (1 mm2 surface area and c. 500 µm thickness) were taken with a micro-scalpel from
the painting surfaces before and after cleaning, and analysed using FTIR spectroscopy in a
potassium bromide (KBr) pellet. The purpose of this was to identify the chemical
Table 1
Composition in % weight of the oil-in-water microemulsions [29] prepared for the
cleaning tests at the Villa del Barone and Loggia del Bigallo
Table 2 Composition in % weight of the micellar solutions prepared for the cleaning tests at the
Prato Cathedral
nature of the patina that was to be removed, and to determine the efficacy of the cleaning agents
used. In some circumstances scanning electron microscopy coupled with energy dispersive X-ray
spectroscopy (SEM-EDX) was used to check if any residues of the SDS surfactant - the only nonvolatile compound present in the micellar solutions or o/w microemulsions -remained on the
painted surface after cleaning.
RESULTS AND DISCUSSION
Microemulsion B (see Table 1) was successfully tested on the frescoes in the Loggia del Bigallo in
Florence for the removal of deteriorated organic materials containing egg and animal glue,
introduced by Giovanni Bianchi at the beginning of the nineteenth century during the repainting of
the wall with tempera-based pigments. The presence of these substances and also oxalates was
determined by FTIR analysis of a sample taken in the vicinity of the area upon which
microemulsion B was applied. The oxalates are most probably products of the deterioration of the
tempera organic binding media used by Bianchi [31-33]. The application methodology employed
for this test was as follows. Microemulsion B was applied to the surface of the wall painting using a
cellulose compress (in order to maximize the contact time between the treatment area and the
cleaning agent) [30]. The application time was two hours and the temperature was 29.5 ± 0.5°C.
After removal of the compress the surface was cleaned twice with the same microemulsion and then
cleared several times with deionized water. This operation was carried out with the aid of a brush.
Figure 2 shows the area of this cleaning test after complete drying of the wall (two days). The
exact location of the application of the microemulsion compress is indicated by a dotted line. The
brown layer ot degraded organic materials (as indicated by zone 2) was completely removed, and
the original grey colour ot the painting surtace is now visible (zone 1). The complete removal of the
SDS surfactant was confirmed by SEM-EDX analysis of the surface of a micro-sample taken from
the surface of the fresco after treatment. The EDX spectra indicated the presence of the elements
typical of a mortar surface (Ca, Si, Al), but the presence of sodium (a marker for the SDS) was not
observed. It is interesting to note that in similar tests the microemulsion A did not produce such
good results, and so in this particular case it is clear that the ND/p-xylene mixture was a better
solubilizing agent than pure p-xylene. The micellar solutions were not tested, as they are very
highly polar systems, and therefore unsuited for the removal of such hydrophobic polymeric resins.
Tests using the micellar solutions were undertaken during the recent conservation of the fifteenthcentury Filippo Lippi trescoes in the apse of the Cappella Maggiore in Prato Cathedral. The micellar
solutions were found to be very effective cleaning agents for the removal of vinyl materials and
mixtures of acrylic and vinyl polymer resins applied during previous conservation treatments as
consolidants and protectives. The composition ot the micellar solutions C and D used in the
cleaning tests is given in Table 2. An example of one of the test areas is shown in Figure 3, which
shows the characteristic lightened appearance of the wall painting surface (zone 3) due to the
presence of organic coating
Figure 2 Loggia del Bigallo, Florence, Test area for the application of microemulsion B (zone 1).
Zone 2 is untreated.
Figure 3 Prato Cathedral. Raking light image of the test area for micellar solutions C (zone2)
and D (zone1). Zone 3 is untreated.
materials. The micellar solutions were applied using a cellulose compress, using the same
application methodology as described for microemulsion B [31]. The contact time for each
application was two hours and the temperature was between 26 and 28°C. Atter the removal of the
compress, the treated surface was gently brushed over twice with propan-2-ol (isopropanol) and
then cleared many times with deiomzed water in order to remove any residual surfactant. Indeed,
this stage of the treatment requires particular attention, since one of the main problems related to the
use of these systems on painted surfaces is that any residues of the SDS surfactant will crystallize
on drying, and can potentially result in a whitened surface appearance. Figure 3 shows a raking light
image of the area on which the tests using micellar solutions C (zone 2) and D (zone 1) were
conducted, after the surface has been cleared with water and the wall completely dried. One can
observe that the whitened appearance due to the organic polymeric coatings is no longer present in
both of the zones treated with micellar solutions. The cleaning effect is slightly more pronounced
tor zone ® than for zone 55. most probably due to the different amount of active organic solvents
(with the exception of PeOH) in the two systems (micellar solution C contains approximately
12.5% solvent, as opposed to micellar solution D which contains more than 16%). In order to
ascertain the chemical nature of the materials extracted by micellar solution D. a further extraction
from the compress used for the treatment was undertaken using trichloromethane. After the
compress had been removed from the painting surface, it was immersed in 200 mL of
trichloromethane and refluxed for three hours. The solution was then filtered and evaporated. This
resulted in a thin film of organic material, which was then subjected to FTIR analysis. The spectrum
(Figure 4a) shows peaks that are characteristic of a vinyl resin, as confirmed by comparison with
the spectrum of a standard commercial vinavil8 glue (Figure 4b).
The main differences between the micellar solutions developed for these tests and conventional
surfactant (detergent) solutions are as follows: (i) in a conventional detergent solution the cleaning
action is achieved only by the surfactant micelles, whereas in our systems there is a synergistic
action between surfactant micelles and the co-solvents adsorbed at the micellar surface: (n) micelles
increase the solubility in water of most organic solvents (for example, in our case PeOH and PC
[34]): (iii) in our systems the micelles act as nano-sponges with surfaces that have a high
concentration of solvents suitable for the cleaning process.
Figure 4 FTIR spectra of resin extracted from a treatment compress containing micellar solution D
(a), and of a commercially available vinyl glue (vinavil) (b).
Tests using microemulsions A and B at the Villa del Barone, in Montemurlo, Prato, showed that
they are also effective in the removal of oil- and acrylic-based paints sprayed by vandals on the
surface of an eighteenth-century a secco wall painting. The current common practice for the
removal of these substances is by dissolution using mtro-diluent, acetone, chlorinated solvents and
other organic solvents, either pure or in a mixture. Unfortunately, as discussed above, the use of
organic solvents on porous surfaces can result in the partial redistribution of the unwanted
substances through the porous support. Figure 5 shows how a layer of black oil paint was
completely removed in a few minutes just by brushing the surface with microemulsion A, which
was subsequently cleared several times with deionized water. Good results were also achieved using
microemulsion A in a similar manner to remove a red acrylic-based paint from the same surface, as
illustrated in Figure 6a (before treatment) and 6b (after application of the microemulsion). In this
particular case there was no observable difference in performance of microemulsions A and B, most
probably because the paint that was being removed was highly soluble in p-xylene.
CONCLUSIONS
The experimental results indicate that both microemulsions and micellar solutions are effective in
the solu-bilization and removal of organic materials such as vinyl and acrylic resins from painted
surfaces. This has been
Figure 5
Villa del Barone, Prato, Italy. Test area for the application of microemulsion A to
remove oil-paint, before (left) and after (fight) the application of the microemulsion.
Figure 6 Villa del Barone. Prato. Italy. Test area for the application of microemulsion A for the
removal of spray paint before (A) and after (B) the application of the microemulsion.
confirmed by FTIR spectroscopy studies. Therefore, these systems can be proposed as an
alternative and innovative tool tor use in art conservation. In particular, the development of these
systems presents two major advantages:
1
The amount ot the organic active phase required is significantly reduced, and therefore the
impact on the environment by such treatments is diminished.
2
The redistribution of solubilized materials into the porous matrix is minimized by the
compartimental-ized solubilization that occurs either inside the hydro-phobic core of the droplets
(microemulsions) or at the interface between the surfactant and the continuous medium
(microemulsions and micellar solutions). Moreover, the continuous aqueous phase constitutes a
hydrophilic barrier to the penetration ot hydro-phobic materials into the support.
It is also important to note that the selection criteria governing the choice of one microemulsion
over another, or indeed a micellar solution, are closely associated with the chemical nature of the
hydrophobic material that is to be removed and the most suitable organic solvent for its
solubilization. In other words the dispersed system is developed from the outset by selecting the
best solvent - for example, referring to the Teas charts [4] — and then selecting the most
appropriate dispersing system (microemulsion or micellar solutions) in order to achieve the best
performance.
The potential availability of a very large number of these dispersed systems makes this approach
very interesting and innovative since it is possible to create, on an ad hoc basis, microemulsions or
micellar solutions tor the removal of a wide range of organic materials from painted surtaces. This
affords the conservator a more sophisticated approach to treatment through the development of
cleaning agents that are specifically tailored to suit the conservation needs of the individual object,
and presents a fascinating area tor future research.
ACKNOWLEDGEMENTS
The authors express their deep gratitude to Drs Arch. M. Lolli Ghetti. D.A. Valentino and M. Del
Buono, to Drs I. Lapi Ballerini, C. Gnoni and L.M. Medri. and to Geom. F. Vestri, Soprintendenza
per i Bern Archi-tettomci e per il Paesaggio di Firenze Prato e Pistola who allowed the experiments
with the new cleaning systems developed in the present study. Thanks are also due to the
conservators Fratelli Piacenti. S. Giovannoni, A. Felici and M. Gittins for undertaking cleaning tests
in the workshops.
SUPPLIERS
P-xylene. sodium dodecylsulphate. pentan-1-ol. propan-2-ol and propylene carbonate: Fluka.
Industriestrasse 25. CH-9471 Buchs SG. Switzerland.
Benzyl alcohol: Carlo Erba Reagenti. Strada Rivokana Km. 6/7. 2009(1 Ródano (Mi). Italy.
Commercial nitro-dilucnt: Starcolor srl., via Bellagio. 50141 Florence. Italy.
REFERENCES
1 Gombrich. E.-H.. Kurz. O.. Iones. S.R.. and Plesters. J.. 'La "Battaglia" di Paolo Uccello". in Sul
Restauro, ed. A. Conti. Einaudi. Torino (1988) 74-78.
2 Ciabach. !.. 'Investigation ot the cross-linking ot thermoplastic resins effected by ultraviolet
radiation', m Promediaos of the Symposium 'Resins in Conservation'. Scottish Society tor
Conservation and Restoration. Edinburgh (1982) 5.1-5.8.
3 Luskin. L.S.. 'Acrylic acid, methacrylic acid and the related esters', m Vinyl and Diene
Monomers, part 1. ed. E.G. Leonard. Wiley Interscience. New York (1970) li 15-204.
4 Hone. C.V.. Materials for Conservation: Organic Consolidants. Adhesiva and Coatings. 1st edn.
Architectural Press (Butterworth-Hememann). Oxford (1987).
5 Tintori. L.. 'Studies for the preservation ot the trescoes by Giotto m the Scrovegni Chapel at
Padua. I. The state ot conservation of the frescoes and the principal technical conservation
problems'. Studies in Conservation 8 (1963) 37— 41.
6 Masaaki. S.. 'The consolidation and the conservation ot ancient Japanese wall paintings', m
International Symposium on the Conservation and Restoration ot Cultural Property. National
Research Institute of Cultural Properties. Nara (1996) 211-°25
7 Mora. P.. and Mora Sbordoni. L.. 'The Nefertan conservation program', in. Art and Eternity: The
Xetertari ]]'all Paintings Conservation Project, 1986-1992. ed. M.A. Corzo and M. Afshar. Getty
Conservation Institute. Los Angeles (1993) 67— 81.
8 Prevost-Marchilancy. C. 'Ancienne collégiale Samt-ßarnard de Romans: décor du choeur et du
transept', m Architecture et Décors Peints, Direction du Patrimoine. Amiens (19911) 73-74.
9 Espinosa, A., 'Conservation and restoration of the murals of the Temple of the Paintings in
Bonampak. Chiapas', in In Situ Archaeological Consewation. Instituto Nacional de Antropología e
Historia. J. Paul Getty Trust. Mexico (1986) 84-89.
10 Cappella degli Scrovegni, Dipíuti Murali, unpublished report. Capitolato Spéciale cTAppalto.
Istituto Centrale per il Restauro, Rome (2001).
11 Feller, R.L.. 'Influence of wavelength', in Accelerated Aging -Photochemical and Viermal .ispeas, ed. R. L. Feller. The Getty Conservation Institute. Los Angeles (1994) 63-90.
12 Morimoto, K., and Suzuki. S.. 'Ultra-violet irradiation ot poly(alkyl acrylates) and poly(alkyl
methacrylates)'. Journal of Applied Polymer Science 16 (1972) 2947-2961.
13 Feller. R.L.. "Speeding up photochemical deterioration". Bulletin de l'Institut Royal du
Patrimoine Artistique 15 (1975) 135-150.
14 Hennig. J., 'Photooxidative Abbau m Abhängigkeit von Wellenlänge und Schichttiefe am
Beispiel PMMA'. Kunststoffe Fortschriftsbenchte 7 (1978) 1 3-22.il 5 .Carretti. E., ei, L.,
Miliani, C, and Baghom. P.. 'Oil-m-water microemul-sions to solubilize acrylic copolymers:
application in cultural heritage conservation*. Progress in Colloid and Polymer Science 118 (2001)
63-67.
16 Papoutsi. D.. Lianos. P.. and Brown. W., 'Interaction of polyethylene glycol with water-in-oil
microemulsions. 3. Effect of polymer size and polymer concentration'. Liingnnur 10 (1994) 34023405.
17 Cabane. B.. "Structure of some polymer-detergent aggregates m water". Journal of Physical
Chemistry 81(17) (1977) 1639— 1645.
18 Simionesco. C.A., Texeira. J.. and Angell, CA., 'Structural characterization of glass-torniing
oil/water microemulsions by neutron scattering'. The Journal of Chemical Physics 91(1) (1989)
395—100.
19 Arvidson. A., and Sodennann. O.. 'The microemulsion phase in the didecyldimethylammomum
bromide/dodecane/water system. Phase diagram, microstructure, and nucleation kinetics of excess
oil phase'. Langmuir 17. (2001) 3567-3572.
20 Garn. N.. Yaghmur. A., Leser. M.E.. Clement, V., and Watzke. H.G.. 'Improved oil
solubilization in oil/water food gracie microemulsions m the presence ot polyols and ethanol",
Journal of Agricultural Food Chemistry 49 (2001).
21 Ranee. D.G.. and Fneberg, S., 'Micellar solutions versus microemulsions', journal of Colloid
and Interface Science 60 (1977) 207-209.
22 Ferroni. E-, Gabrielli, G.. and Caminan, G.. Process for Cleaning Hydrophobie Porous
Matrices. European patent 91105096 (1991).
23 Ferroni. E.. Gabrielli. G.. and Caminati, G.. 'Removal of hydrophobic impurities from pictorial
surfaces by means of heterogeneous systems'. Science and Technology for Cultural Heritage 4(2)
(1995) 67-74.
24 Acosta. E.. Szekeres. E.. Sabatmi. D.A.. and Harwell, J.H., 'Net-average curvature model for
solubilization and super-solubilization in surfactant microemulsions', Langmuir 19 (2003) 186-195.
25 Robb, I.D., and Stevenson, P.S., 'Solubilization of trilaurin in surfactant solutions'. Langmuir
16 (2000) 7939-7945.
26 Kim. J.-H., Domach, M.M., and Tilton, R.D., "Effect of electrolytes on the pyrene solubilization
capacity of dodecyl sulfate micelles'. Langmuir 16 (2000) 10037-10043.
27 Leung. R.. Hou. M.J., and Shah, D.O., 'Microemulsions: formation, structure, properties, and
novel applications', m Suiiactants in Chemical Process Engineering, ed. D.T. Wasan, M.E. Ginn
and D.O. Shah, 1st edn, Dekker, New York (1988) 333-341.
28 Sonntag. N.O.V.. 'Surfactants in aqueous emulsification separation of oleic and stearic acids',
in Surfactants in Chemical/ Process Engineering, ed. D.T. Wasan, M.E. Ginn and D.O. Shah. 1st
edn, Dekker, New York (1988) 169-194.
29 Carretti. E.. Dei. L.. and Baglioni, P., Microemulsioni ed Emulsioni di Olio in Acqua, loro Uso
per la Solubilizzazione di Resine Polimeriche e Impacchi contenenti dette Microemulsioni ed
Emulsioni, Italian patent FI/99/A/000071 (1999).
30 Ferroni, E.. and Dini, D., 'Prospettive per la conservazione degli affreschr. in Scritti di Storia
dcll'Ane in Onore di Ugo Procacci, Electa Editrice, Florence (1977) 17-22.
31 Polesello. S., and Toniolo, L., 'Calcium oxalate in mural paintings: recoveries on northern
Italian frescoes', in Inter-national Symposium ill): the Oxalate Films in the Conservation of
Works of Ar!, ed. M. Realmi and L. Tomólo. Editeani. Milan (1996) 233-253.
32 Cariati. F., Rampazzi, L.. Tomólo. L.. and Pozzi. A.. 'Calcium oxalate films on stone surfaces:
experimental assessment ot the chemical formation', Studies in Conservation 45 (2U00) 18n-188.
33 Camaiti. M.. Fommei. C. Giammello. M.. and Sabatini. G.. 'Treatment of stone surfaces
according to ancient recipes: first results on the formation of calcium oxalates". m IinenitUioujI
Symposium II: Tlie Oxalate Films in tlie Couseiv^tion ot ]\orks of Art, ed. M. Realini and L.
Tomólo. Editeam. Milan (19%) 285-298.
34 Carreta, E., Dei. L.. and Bagliom. P.. 'Solubilizafion of acrylic and vinyl polymers in
nanocontainer solutions. Application of microemulsions and micelles to cultural heritage
conservation. Lcingmuir 19 (2U03) 7867-7872.
AUTHORS
EMILIANO CARRETTI graduated m chemistry in 1999 from the University ot Florence. Faculty
ot Sciences. He completed his PhD in science for cultural heritage conservation at the University ot
Florence in 2003, and is currently a temporary researcher at the Chemistry Department of the
University of Florence. Address: Dipartimento di Chímica & CSGI Consortium, Université degli
Studi di Firetize, via delta Lastruccia, 3 I-50019 Sesto Fiorentino (FI), Italy. Email:
carrctti(wcsgi.unift.it
BARBARA SALVADORI graduated m chemistry in 2000 from the University of Florence,
Faculty of Sciences. She completed her PhD in science tor cultural heritage conservation at the
University ot Florence in 2004, and is currently a temporary researcher at the CSGI Consortium of
the Chemistry Department of the University ot Florence. Address: as for Canetti. Email: sah
'adoriCctcsgi. unifi.it
PIERO BAGLIONI is a full professor of physical chemistry at the Faculty" of Sciences of the
University of Florence. He has authored over 200 publications m the field of colloids and interlaces,
and physical chemistry applied to the conservation of works of art. He lectures m physical
chemistry, physical chemistry of colloid and interfaces, and chemistry of conservation at the
Faculty of Sciences of the University of Florence, and is a scientific consultant for many national
and international conservation projects. In 2002 he was awarded the European Rhodia Prize and in
2003 the Jury's Grand Prix of the European Grand Prix for Innovation. Address: as for Canetti.
Email: bagliouilQcsgi.unifi.it
LUIGI DEI is an associate professor of physical chemistry at the Faculty of Sciences of the
University of Florence. He has authored about 100 publications in the fields of colloids and
interfaces, and physical chemistry applied to the conservation of works of art. He lectures m
biological physical chemistry and chemistry of conservation at the Faculty of Sciences of the
University of Florence, and also in environment and cultural heritage chemistry at the Faculty of
Human Sciences of the same university. He is president of the university course in technology for
cultural heritage conservation at the Faculty of Sciences of the University ot Florence for the
academic years 2001—2007. He is a scientific consultant tor many national and international
conservation projects. Address: as for Canetti. Email: dei@xsgi.utnfi.it
Résumé — Cet article présente une nouvelle approche pour l'élimination de matériaux
hydrophobes de la surface des peintures murales. Des systèmes natiostntcturés ayant des propriétés
physico-chimiques bien définies sont proposés comme alternative aux solvants organiques pour
solubiliser les substances se trouvant sur les surfaces peintes poreuses. En raison du large éventail
de composants pouvant être utilisés pour leur préparation, ces systèmes peuvent potentiellement
servir à éliminer un grand nombre de types de matériaux organiques différents. On présente les
résultats d'expériences utilisant des micro-émulsiotis huile/eau et des solutions micellaires comme
agents nettoyants. L'efficacité de ces systèmes a été testée dans plusieurs ateliers de conservation
italiens pour éliminer différents matériaux hydrophobes. En particulier, ils ont été utilisés avec
succès lors de la conservation des fresques de la Loggia del Bigallo à Florence (souillées par des
matériaux organiques dégradés) et pour éliminer diverses résines organiques synthétiques de la
surface des fresques de Filippo Lippi dans l'abside de la chapelle majeure de la cathédrale de
Prato. De plus, ces micro-émulsions se sont également révélées efficaces pour éliminer les
peintures à base d'un mélange huile-acrylique utilisées par des vandales pour barbouiller des
peintures a secco du dix-huitième siècle à la Villa del Barone à Prato. Les résultats sont illustrés
par une documentation photographique détaillée et par des spectres IRTF.
Zusammenfassung — In dieser Arbeit wird ein neuer Versuch zur Entfernung hydrophober
Materialien von der Oberfläche von Wandmalereien präsentiert. Xanostrukturelle Systeme mit gut
charakterisierten physikochemischen Eigenschaften werden als Alternative zu nicht unterstützten
organischen Lösungsmitteln für das Ablösen von Substanzen auf porösen Oberflächen
vorgeschlagen. Entsprechend der Vielzahl unterschiedlicher Komponenten, die zur ihrer
Herstellung verwendet werden können, können diese Systeme zur Entfernung verschiedenster
organischer Materialien genutzt werden. Die Ergebnisse von Experimenten, bei denen Öl-inWasser-Emulsionen sowie micellar- Lösungen als Reinigungsmittel für Wandmalereien verwendet
wurden, werden präsentiert. Die Effizienz dieser Systeme bei der Entfernung zahlreicher
hydrophober Materialien wurde in verschiedenen italienischen Werkstätten getestet. Im einzelnen
wurden die Materialien bei folgenden Projekten erfolgreich getestet: bei der Restaurierung der
Fresken in der Loggia del Bigallo in Florenz (durch degradiertes organisches Material natürlichen
Ursprungs geschädigt) und bei der Entfernung verschiedener synthetischer Harze auf der
Oberfläche von Filippo Lippis Fresko in der Hauptkapelle des Domes zu Prato. Darüber hinaus
konnte gezeigt werden, daß Öl-in-Wasser-Emulsionen ein effektives Reinigungsmittel zur
Entfernung von öl- und acrylbasierten Malschichten waren, wie sie von Unbekannten zur
Entstellung einer a seeco Malerei in der Villa del Barone in Prato genutzt wurden. Die Arbeit wird
detailliert
photographisch
dokumentiert
und
durch
Untersuchungen
mittels
Fouriertransforminjrarotspektroskopie unterstützt.
Resumen — Este artículo presenta una nueva técnica para la eliminación de materiales
hidrofóbicos de la superficie de pinturas murales. Se proponen ciertas alternativas basadas en
nanoestructuras con propiedades físico-químicas bien caracterizadas para los disolventes
orgánicos, (no-incluidos en un medio de soporte), con el fin de solubilizar substancias en
superficies pintadas porosas. Debido al amplio rango de componentes que pueden ser usados en su
preparación, estos sistemas pueden ser usados potencialmente para eliminar un amplio abanico de
diferentes tipos de materiales orgánicos. Se presentan los resultados de los experimentos usando
mícroemulsiones de aceite-en-agua y disoluciones micelares como agentes de limpieza para
pinturas murales. La eficacia de estos sistemas ha sido probada en muchos estudios de
restauración italianos para la eliminación de varios materiales hidrofóbicos. En concreto, han sido
usados con éxito durante la restauración de los frescos de la Logqia del Bigallo en Florencia
(afectados por la degradación de materiales orgánicos naturales), y para la eliminación de varias
resinas sintéticas orgánicas de la superficie de los frescos de Filippo Lippi en el ábside de la
Capilla Mayor de la Catedral de Prato. Adicionalmente, las micro emulsiones aceite-en-agua se
han mostrado también como agentes de limpieza efectivos para la eliminación de pinturas de base
acrílica u oleosa, utilizadas por vándalos para desfigurar una pintura del siglo XVIII pintada al
secco en la Villa del Barone en Prato. Los resultados se complementan por una detallada
documentación fotográfica y por espectros infrarrojos por transformada de Fourier.