10.6092/issn.1973-9494/10348
The aim of this study was to explore the use of biotechnologies in the restoration of wall paintings and stuccos which often show a great complexity regarding constitutive materials and conservative conditions. ‘Biological methods’ were compared to traditional methods, focusing on restoring the cohesion of the superficial layers (bioconsolidation) and the removal of sulphates (biocleaning) often found on the frescoes as decay products. The experimentation took place as part of a graduate thesis and was divided in two stages: the first was spent in the laboratory working on samples of painted plaster and the second was spent in situ, on the frescoes and stuccos in the Church of Santa Pudenziana in Rome, Italy. Application of the products was followed by a campaign of investigations aimed at determining the efficacy, and the advantages and disadvantages of these methods compared to conventional ones.
application/pdf
1973-9494
10348
en
Veronica Fondi
Conservation Science in Cultural Heritage
fresco
Biotechnology in the Conservation Field: Removal of Sulphates Using Bacteria and Bioconsolidation of Paintings and Stuccos
Text.Serial.Journal
https://conservation-science.unibo.it/
19
Articles
2020-03-18
2020-01-10
2020-03-18
2020-03-18
157-175
CSCH
Veronica Fondi
2019
10.6092/issn.1973-9494/10348
157
Conservator, Genzano di Roma, Rome
1973-9494
fresco
en
175
Biotechnology in the Conservation Field: Removal of Sulphates Using Bacteria and Bioconsolidation of Paintings and Stuccos
https://conservation-science.unibo.it/article/download/10348/10605
19
B    IOTECHNOLOGY IN THE CONSERVATION FIELD:
      REMOVAL OF SULPHATES USING BACTERIA AND
      BIOCONSOLIDATION OF PAINTINGS AND STUCCOS

  Eleonora Panella*1
  Conservator, Rome, Italy

  Carla Giovannone, Marco Bartolini
  Conservator, Istituto Superiore per la Conservazione ed il Restauro, Rome, Italy

  Veronica Fondi
  Conservator, Genzano di Roma, Rome, Italy


  Keywords: bioconsolidation, biocleaning, bacteria, stucco, fresco


  1. Biorestoration

   Biotechnologies, based on the use of non-pathogenic microorganisms, have
been introduced into the field of cultural heritage conservation due to their positive
properties and the absence of toxic effects for restorers [1]. During the past few
years research has focused on two different areas: “biocleaning” and “bioconsoli-
dation”, two biological processes involving the use of various bacterial strains as
well as different application methods. The aim of this study was to explore the use
of such procedures (usually applied on stone materials) in the restoration of wall
paintings and stuccos, which often present constitutive materials and conserva-
tive conditions of great complexity. In particular, a bio-consolidation process was
tested to re-establish cohesion in the materials of several superficial layers and a
bio-cleaning method was used for the removal of sulphates which are often found
on frescos as decay products. In both cases patented and marketed products
were used. Experiments were conducted as part of the practical stage of a thesis
on conservation by Eleonora Panella, in the Istituto Superiore per la Conservazi-
one ed il Restauro. The actual research was carried out in the Chapel of St. Peter
in the church of Santa Pudenziana in Rome, Italy, on wall paintings and stuccos
from the sixteenth century.


  2. Bioconsolidation

   This treatment, aimed at restoring mechanical strength and internal cohesion in
natural and artificial stone materials, is based on “biocarbonatogenesis”, a natu-
ral process that occurs in many environments and is related to the formation of
carbonate sediments and rocks. The phenomenon of bioprecipitation is very com-


*1 Corresponding author: eleonorapanella@yahoo.it
                                                               plex and can be influenced by the physical-chemical parameters, metabolism and
                                                               structure of the various bacterial strains.
                                                                  Products derived from the metabolic activity of calcinogenic bacteria are new
                                                               minerals, very similar to those that constitute the substrates of the artworks. Bio-
                                                               consolidation treatments produce mainly two minerals, calcite and vaterite. Once
                                                               released from the bacteria, these minerals accumulate in the porous spaces of the
                                                               material and, by doing so, restore its cohesion.
                                                                  The formation of calcite crystals begins on the surface of the bacterial cell, the
                                                               cell wall, which contains a considerable number of functional groups such as phos-
                                                               phates, hydroxyls and carboxyls, highly reactive to metallic ions such as Ca++ found
                                                               in the environment surrounding the cell. Since Ca++ ions are not used in large
                                                               quantities in intracellular metabolic processes, they accumulate on the surface of
                                                               the bacterial cell. When the metal ion Ca++ is complexed, it becomes the nucleation
                                                               center on which the subsequent mineral crystals are formed. After the nucleation,
                                                               crystalline structures develop, incorporating the bacteria themselves [2].
                                                                  Studies on bio-induced calcite precipitation began in the 1980s in France and
                                                               there are currently several European projects that are conducting experiments on
                                                               the bioconsolidation of stone materials. Although most of the studies carried out
                                                               so far relate to the consolidation of natural stone artifacts, for some years several
                                                               research groups have been seeking to expand the types of artifacts on which such
                                                               treatment can be carried out.
                                                                  Among the various bioconsolidation treatments that are available, the present
                                                               study focuses on the method developed by Dr. M.T. Gonzalez-Muñoz of the De-
                                                               partment of Microbiology of the University of Granada, which provided the prod-
                                                               ucts and consulting for the application [3-8].
E. Panella et al. - Biotechnology in the conservation field




                                                                 2.1. M-3P product

                                                                   Initially, this research team proposed the use of Myxococcus xanthus as a bac-
                                                               terial strain capable of inducing the biomineralization of calcium carbonate.
                                                                   Following further studies, a method was developed without the use of bacterial
                                                               cells and therefore completely safe for the operator [9]. The procedure is based on
                                                               the use of a culture medium called M-3P, which stimulates the calcinogenic activity
                                                               of bacteria already present in the microbiota inhabiting the surfaces [10].
                                                                   M-3P is a sterile nutritional solution made of 1% Bacto Casitone (a pancreatic
                                                               digest of casein), 1% Ca (CH₃ COO)₂•4H₂O, 0.2% K₂CO₃•1/2H₂O in a 10 mM
                                                               phosphate buffer (pH 8) [11].
                                                                   The use of Bacto Casitone as a source of carbon and nitrogen causes alka-
                                                               linization due to ammonia acidification involving the formation of ammonia, which
                                                               results in an increase in pH. In the alkaline environment, with the lower concentra-
                                                               tion of H⁺ ions, the balance of the reaction between carbonate and bicarbonate
                                                               moves towards the production of carbonate ions:

                                                                                              HCO₃ˉ ↔ CO₃ˉ ˉ + H⁺




                                                         158
  In the presence of Ca⁺⁺ calcite is produced

                            Ca⁺⁺ + CO₃ˉ ˉ ↔ CaCO₃. [9]


  2.2. Experimental procedure and Application

   The University of Granada provided the product M-3P, which was tested along
with other consolidation treatments. This bioconsolidation process was compared
with the conventional consolidants most frequently used to restore the cohesion of
painted and stucco plasters: colloidal nano-particles of Ca(OH)₂1 and acrylic resin2.
   The experimental procedure was structured in the following phases:
   1) definition of materials and methods for investigations on samples and in situ;
   2) production of samples, using the same techniques as for the original arte-
facts. For the stucco samples marble powder and lime were used, while painted
plaster samples were made of pozzolana, lime and inorganic pigments;
   3) identification of sample areas with severe lack of cohesion on frescos and
stucco decorations in situ;
   4) application of the consolidating products on painted plaster and Roman
stucco samples, on detached erratic fragments of frescoes and stuccoes and on
sample areas of the fresco and stucco in the Chapel of St. Peter.
   5) evaluation of effectiveness by means of contact sponge method, peeling
tape test, contact angle measurement on samples of painted plaster and Roman
stucco, SEM analysis on detached erratic fragments from fresco and stucco.
   Nanolimes were applied on the samples by impregnation, using a brush; acrylic
resin and M-3P were sprayed onto the surfaces (Figure 1). After application of the
products the samples were left in the Chapel of St. Peter for one month, to allow
deposition of the same biocontaminants already present on the frescos and stuc-




                                                                                              CONSERVATION SCIENCE IN CULTURAL HERITAGE
cos in situ, to take place.
   Erratic fragments were treated only with M-3P, in order to carry out investiga-
tions to evaluate the effectiveness of the product.
   In situ, M-3P was applied to the previously selected sample areas, choosing
different colour layers, to take into consideration the possible interference of the
product with the pigments.
   M-3P application was performed in the summer to ensure a suitable tempera-
ture for bacterial growth. The product was applied up to saturation three times a
day for six consecutive days, on samples, on erratic fragments and in situ.




                                                                                        159
E. Panella et al. - Biotechnology in the conservation field




                                                               Figure 1. Application of the M-3P product by spraying it on the different surfaces: (A) on samples;
                                                               (B) on wall paintings; (C) on stuccos; (D) on erratic fragments (Photo: Eleonora Panella).



                                                                  2.3 Evaluation of efficacy

                                                                  The tests were carried out before and after the treatments. Thanks to the use of
                                                               samples, it was possible to make repeated measurements and so collect many data.
                                                               These data were processed into charts that helped to highlight the results. Finally,
                                                               an overall reading made it possible to evaluate the effectiveness of the different
                                                               treatments.

                                                                  Contact sponge method3: a reduction in water absorption was recorded for all the
                                                               consolidation treatments analyzed. On the stucco samples, the best results were ob-
                                                               tained with the M-3P product; on the plaster samples, the major reduction occurred
                                                               with the acrylic resin (Figure 2).




                                                         160
                                                                                           CONSERVATION SCIENCE IN CULTURAL HERITAGE
            Figure 2. Reduction of water absorption after treatment on samples.



  Peeling tape test: the application of acrylic resin showed the best result when
compared with the untreated sample. Where the acrylic resin was used, in fact, the
peeling tape caused less pigment detachment from the surface than where M-3P
was used (Figure 3).




                                                                                     161
                                                               Figure 3. Amount of pigment detached after consolidation compared to the untreated surface
                                                               (Images from the ISCR biology lab).



                                                                  Contact angle measurement4: the contact angle could not be measured be-
                                                               fore the treatments as the drop was absorbed too quickly by the surface. After
                                                               the treatments, it was possible to measure the contact angle on both stucco and
                                                               painted plaster samples treated with acrylic resin and stucco samples treated with
                                                               M-3P (Figure 4).
E. Panella et al. - Biotechnology in the conservation field




                                                                                  Figure 4. Contact angle measurements after treatments



                                                                  SEM and XRD: these tests were run only on erratic stucco and plaster fragments
                                                               treated with M-3P in order to evaluate the efficacy of the bio-consolidation process.
                                                                  Calcium enrichment was observed on the fragments (Figure 5). However, it was
                                                               difficult to quantify the formation of bacterial calcite because it could have been
                                                               masked by the large amount of calcite present in the untreated sample (before
                                                               treatment).


                                                         162
                                                                                                           CONSERVATION SCIENCE IN CULTURAL HERITAGE




Figure 5. SEM-EDS of the stucco surface after treatment. Calcite crystals are visible (Images from
the ISCR biology lab).



    The diffractometric investigation, in this case, proved ineffective because cal-
cium carbonate is the main constituent material of the plaster in the fresco and of
the Roman stucco.
    It is important to specify that the results of the analyses are related to the spe-
cific areas where the samples were taken from and therefore may not be repre-
sentative of the general situation.


                                                                                                     163
                                                                  2.4 Evaluating interference

                                                                  A first evaluation of interference of the treatment was performed on the basis
                                                               of the visual comparison between the samples. In particular, two aspects were
                                                               considered: the yellowing potential of the nutrient medium, which is of a slightly
                                                               yellowish colour and possible whitening from the newly formed calcite. Colorimet-
                                                               ric measurements were performed in situ on all fresco samples.

                                                                  Colorimetric measurements: on stucco samples treated with M-3P, colorimetric
                                                               measurements showed a mild yellowing, while no remarkable variations were ob-
                                                               served on the fresco samples (Figure 6). In addition, the surfaces treated in situ
                                                               with M-3P did not show any relevant variation in colour.
E. Panella et al. - Biotechnology in the conservation field




                                                               Figure 6. On the left the untreated stucco sample; on the right the sample treated with M-3P,
                                                               slightly yellowed (Photo: Eleonora Panella).



                                                                  Biological growth control: it was also necessary to check the growth of potential
                                                               biodeteriogens, such as fungi, due to M-3P application. To this end, half the sur-
                                                               face of a painted plaster sample was treated with M-3P following the same proce-
                                                               dure used in situ. Subsequently, the sample was left in the Chapel of St. Peter for
                                                               about 2 months, after which it was placed in a dryer, maintaining relative humidity
                                                               conditions close to 100% for about 30 days. At the end of this period visual and
                                                               stereo-microscope observation showed the growth of fungi colonies on the sur-
                                                               face of the sample where M-3P had been applied (Figures 7-8), while no growth
                                                               was detected on untreated areas. At least three species of fungi had developed in
                                                               small colonies, distributed homogeneously on the treated areas.




                                                         164
Figure 7. Stereomicroscope images of fungi grown on the part of the sample treated with M-3P
(Images from the ISCR biology lab).




                                                                                                     CONSERVATION SCIENCE IN CULTURAL HERITAGE



Figure 8. SEM image of plaster fragments treated with M-3P. Presence of fungal hyphae and
extracellular polymeric substances (Images from the ISCR biology lab).



   2.5. Considerations

   M-3P showed different capacities depending on the materials on which it was ap-
plied. In fact, a good level of cohesion to the stucco was obtained but no evident differ-
ence was obtained on the painted surfaces.
   The acrylic resin, on the other hand, showed good consolidating properties both on
the stucco and painted plasters as proven by the reduced water absorption, the mild
water-repellent effect on the plaster and the results of the peeling tape test.


                                                                                               165
                                                                  The present study has therefore shown that this bioconsolidation process has
                                                               a consolidating effect despite having lower efficacy than the acrylic resin. If the
                                                               constitutive material is not excessively degraded, the M-3P product offers some
                                                               advantages over chemical processes; however, if there is a particularly severe
                                                               lack of cohesion, this method may be inefficient.
                                                                  The advantages of M-3P over chemical processes are that it does not require
                                                               the use of chemicals and solvents, it is easy to apply, and it is totally compatible
                                                               with carbonate substrates.
                                                                  However, it is less effective than acrylic resin, especially on plaster; the ap-
                                                               plication procedure so far proposed is rather rigid and cannot be adapted to the
                                                               different situations as in the case of conventional treatments; the treatment also
                                                               requires relatively high temperatures and, if applied in environments with high
                                                               humidity, could cause potentially harmful biodeteriogenic growth.


                                                                  3. Biocleaning

                                                                  Biocleaning is an eco-friendly technology that uses living organisms and/or their
                                                               enzymes as cleaning agents through their metabolic processes [12]. The bacteria
                                                               used to remove specific substances from a substrate, are non-pathogenic and
                                                               non-sporogenic, therefore this method is safe both for the worker and the artwork.
                                                                  Cleaning with bacteria can have advantages over other biological methods al-
                                                               ready in use in the cultural heritage field (e.g. enzyme processes). That is because
                                                               enzymes are very selective but when it comes to more complex decay products,
                                                               they are often incapable of removing them completely. Bacteria, on the other
                                                               hand, have a pool of enzymes which guarantee selectivity as well as the ability to
E. Panella et al. - Biotechnology in the conservation field




                                                               act on a wider range of substances. Furthermore, microorganisms can adapt very
                                                               well to various environmental conditions which means application is easier for the
                                                               operator to perform.
                                                                  Early studies on the use of bacteria to remove decay products or other sub-
                                                               stances date back to the end of the 1980s and have been directed especially at
                                                               the removal of protein substances and at salt reduction on stone materials and
                                                               wall paintings [13-21].
                                                                  This study has focused on the removal of sulphates using a bacterial formula-
                                                               tion consisting of sulphate-reducing bacteria. For the bio-cleaning tests a partner-
                                                               ship was established with the company Micro4you (Dr. A. Balloi), a spin-off com-
                                                               pany of the University of Milan, which supplied the product Micro4Art.


                                                                  3.1. Micro4Art

                                                                  Micro4Art is a lyophilized formulation characterized by a high concentration of Des-
                                                               ulfovibrio Vulgaris. This bacterial species is part of the anaerobic soil bacterial flora,
                                                               so it does not require the presence of oxygen to survive. It uses sulphate as an elec-
                                                               tron acceptor, transforming it into hydrogen sulphide, which, at ambient temperature,
                                                               evaporates without leaving any residues.

                                                                  6CaSO₄ + 4H₂O + 6CO₂  6CaCO₃ + 4H₂S + 2S + 11O₂


                                                         166
   Calcium ions (Ca2⁺), derived from the gypsum during the process, react with
carbon dioxide, resulting in the formation of calcite (CaCO₃) which penetrates into
the substrate, producing a mild consolidating effect [22-23].
   The application method includes the following:
   – application of the bacterial suspension by means of a suitable supporting
gelling agent which guarantees surface humidification throughout the treatment;
   – use of a plastic film covering the surface to prevent water evaporation and
to reduce the oxygen supply in order to improve the ability of the bacteria to me-
tabolize sulphates;
   – bacteria removal followed by a soft cleaning with sponges and deionized wa-
ter to eliminate residuals.
   Since the treatment is highly influenced by the application method, the tests
were mainly directed at defining an application method that would facilitate its use
in situ and, in particular, to find a supporting agent suitable for vertical surfaces.
   The trial procedure was structured in the following phases:
   1) verification of the presence of sulphates as decay products on the fresco in
the Chapel of St. Peter by conductivity measurements and chemical kits for the
detection of sulphates and nitrates;
   2) selection of the most suitable supporting agent for the application of bacteria
and development of the treatment procedure through laboratory tests on samples;
   3) identification of sample areas on the fresco, characterized by uniform sul-
phate efflorescence;
   4) removal of sulphates using the bioformulation applied with different gelling
agents, compared to traditional methods;
   5) evaluation of its effectiveness by means of conductivity measurements; sul-
phate analyses with chemical kits on extractive compresses of cellulose pulp;
SEM investigations with EDS analysis on small samples of the fresco.
   The bio-formulation was tested, in situ, along with three different supporting




                                                                                               CONSERVATION SCIENCE IN CULTURAL HERITAGE
agents:
   – neutralized polyacrylic acid5 + Micro4Art
   – gellan gum6 + Micro4Art + synthetic mesh
   – natural seaweed agar agar7 + Micro4Art
   The gelling agents were also applied on the surface without bioformulation in
order to evaluate their influence on the biocleaning procedure.
   Finally, the bioformulate was compared to a traditional chemical method:
   – a solution of 5% ammonium bicarbonate in deionized water gelled with hy-
droxypropyl cellulose8 and cellulose pulp (Figure 9).




                                                                                         167
                                                               Figure 9. Test showing the different cleaning systems on the fresco surface (Photo: Eleonora
                                                               Panella).



                                                                  The best system to apply the Micro4Art bioformulation proved to be the one with
                                                               gellan gum + Micro4Art + synthetic mesh (Figure 10) because:
E. Panella et al. - Biotechnology in the conservation field




                                                                  – it allows the bacteria to be inserted in the gel;
                                                                  – it gradually releases the water on the surface while maintaining the right degree
                                                               of moisture for the bacteria;
                                                                  – it leaves very few residues.




                                                               Figure 10. (A) Micro4Art + gellan gum Kelcogel ready to be put on the surface; (B) application on
                                                               the fresco surface (Photo: Eleonora Panella).




                                                         168
  3.2 Evaluation of efficacy

   The efficacy of the various methods was evaluated by measuring the amount of
residual sulphates after treatment compared with the untreated surface.

   Conductivity measurements: showed a significant reduction of ions on the areas
treated with the traditional system and with agar agar + Micro4Art (Figure 11).




                                                                                            CONSERVATION SCIENCE IN CULTURAL HERITAGE
                  Figure 11. Histogram with conductivity measurements



   Sulphates control test: the assay showed that the traditional system produces
a considerable decrease in sulphates, while the agar agar + Micro4Art and gellan
gum Kelcogel + Micro4Art procedure only slightly reduce sulphate concentrations.
In the area treated with Carbogel + Micro4Art the sulphate concentration was
equivalent to the untreated area (Figure 12).
   SEM / EDS: this investigation proved to be more reliable in evaluating the ef-
ficacy of treatments, since the sulphur mapping allows clearer observation of the
residues.
   They showed that the traditional method is the most effective in the removal of
sulphates, followed by gellan gum Kelcogel + Micro4Art. In fact, only a few sulphur
residues are visible on the samples collected from the areas treated with these
two procedures. On the other hand, on the areas treated only with the gelling
agents, a consistent and uniform layer of sulphates is visible (Figure 13).



                                                                                      169
                                                                       Figure 12. Histogram with sulphate and nitrate concentrations after cleaning.



                                                                 4. Conclusion

                                                                  This study highlighted that the traditional procedure is slightly more effective
                                                               than the gellan gum Kelcogel + Micro4Art system and that the gelling agent, sup-
E. Panella et al. - Biotechnology in the conservation field




                                                               porting the bioformulation, highly influences the efficacy of the treatment. The
                                                               advantage, is the high selective action that does not involve the use of solvents or
                                                               chemical substances, making it completely non-toxic. Among the disadvantages,
                                                               especially if compared to the traditional procedure with ammonium bicarbonate, is
                                                               the high cost of the bioformulation-support system, along with the preparation time
                                                               of the products and the rather lengthy application times.




                                                         170
                                                                                                   CONSERVATION SCIENCE IN CULTURAL HERITAGE




Figure 13. SEM-EDS sulphur mapping of fresco fragments (Images from the ISCR biology lab).



  Acknowledgments

   The Authors thank Dr. Maria Teresa Gonzales-Muñoz from the University of Gra-
nada for her cooperation and Dr. Annalisa Balloi from Micro4You.
   Special thanks to the thesis supervisors and to the Istituto Superiore per la Con-
servazione ed il Restauro in Rome, Italy.




                                                                                             171
                                                                   Notes

                                                               1
                                                                      Calosil IP5, IBZ- Salzchemie GmbH & Co.KG.
                                                               2
                                                                      Dispersion K52, Kremer Pigmente.
                                                               3
                                                                      The tests were performed in accordance with the UNI 11432: 2011 standard.
                                                               4
                                                                      The tests were performed in accordance with the NORMAL – 33/89 standard.
                                                               5
                                                                      Carbogel.
                                                               6
                                                                      Kelcogel, CP Kelco.
                                                               7
                                                                      AgarArt.
                                                               8
                                                                      Klucel G at 3% in the ammonium bicarbonate solution.



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                                                                 Biographical notes

                                                                   Eleonora Panella was born in Rome in 1982. From 2001 to 2003 she attended the
                                                               professional institute for restoration Ars Labor. In 2015 she obtained her degree from
                                                               the Istituto Superiore per la Conservazione ed il Restauro in Rome with a dissertation
                                                               on the restoration of late sixteenth century wall paintings and stuccos and on biotech-
                                                               nologies applied to cultural heritage. Since 2004 she has worked in the conservation
                                                               field and currently collaborates with ISCR.

                                                                   Carla Giovannone is conservator of cultural heritage, graduate and majored in
                                                               Restoration and Conservation of Cultural Heritage at the Istituto Centrale per il Res-
                                                               tauro in Rome and also in Medieval Art History at “La Sapienza University” in Rome;
                                                               she is a Restoration Officer at the Higher Institute for Conservation and Restoration
                                                               (ISCR), Laboratory of Wall Paintings and Plasters. From 2018, she is a member
                                                               of the Scientific Council of the aforementioned Institute. She is a lecturer at the
                                                               ISCR Higher Education and Study School for the Master’s Degree in Restoration
                                                               and Conservation of Cultural Heritage (LMR / 02), Decorated Architectural Surfaces.
                                                               She carries out restoration activities on wall paintings and stucco decorations, natu-
                                                               ral stone materials and decorated surfaces. From 2012-2016 she was a lecturer at
                                                               “La Sapienza University” of Rome in the School of Specialization in Architectural
                                                               and Landscape Heritage for the study and restoration of monuments, with special-
                                                               ist theoretical lectures on inorganic binders and mortars and on consolidation sys-
                                                               tems. From 2016 she is a contract professor for MIUR (Ministero dell’Istruzione,
                                                               dell’Università e della Ricerca) at the Academy of Fine Arts in L’Aquila for the degree
                                                               course in Restoration and Conservation of Cultural Heritage (LMR / 02), Decorated
                                                               Architectural Surfaces. She has authored 29 scientific publications on topics related
E. Panella et al. - Biotechnology in the conservation field




                                                               to studies, experiments and conservative interventions on wall paintings, stuccos,
                                                               mosaics, architectural decorated surfaces.

                                                                   Marco Bartolini graduated in Biological Science in 1994 at Tor Vergata Univer-
                                                               sity of Rome. He coordinates the mycology and bacteriology Units and is responsi-
                                                               ble for both the Instrumental and biochemical investigations section and Instrumental
                                                               Techniques of the Biology Laboratory at the Istituto Superiore per la Conservazione
                                                               ed il Restauro (ISCR). Since 2017, he is a member of the Scientific Council of the
                                                               aforementioned Institute. Since 2017 he is vice-director at ISCR Higher Education
                                                               and Study School for the Master’s degree course in Restoration and Conservation
                                                               of Cultural Heritage (LMR/02). He is lecturer of “Applied Biology to Cultural Heritage”
                                                               at the ISCR Higher Education and Study School, and at the University of Fine Arts in
                                                               Macerata. His research focuses on the role of fungi and bacteria in the biodeterioration
                                                               of inorganic materials and on the evaluation of the effectiveness of biocides for the
                                                               control of biodeteriogens on artefacts. Member of the Italian UNI -NORMAL Committee
                                                               for the definition of standard methods on the study and the conservation of natural and
                                                               artificial stones. Author of over 70 scientific publications.

                                                                  Veronica Fondi was born in Marino (Rome) in 1987. After obtaining a degree in
                                                               Cultural Heritage at the University of Tor Vergata she attended the Istituto Superiore
                                                               per la Conservazione ed il Restauro in Rome, where she graduated in 2015 with a
                                                               dissertation on the restoration of the roman frescoes in Massenzio’s Villa on the Appia


                                                         174
Antica. Since then she has worked in the conservation field and is currently a Restorer-
Conservator Official at the Ministry of Cultural Heritage and Activities.


    Summary
    The aim of this study was to explore the use of biotechnologies in the restoration
of wall paintings and stuccos which often show a great complexity regarding consti-
tutive materials and conservative conditions. ‘Biological methods’ were compared to
traditional methods, focusing on restoring the cohesion of the superficial layers (bio-
consolidation) and the removal of sulphates (biocleaning) often found on the frescoes
as decay products. The experimentation took place as part of a graduate thesis and
was divided in two stages: the first was spent in the laboratory working on samples of
painted plaster and the second was spent in situ, on the frescoes and stuccos in the
Church of Santa Pudenziana in Rome, Italy. Application of the products was followed
by a campaign of investigations aimed at determining the efficacy, and the advantages
and disadvantages of these methods compared to conventional ones.


    Riassunto
    Lo scopo di questo studio era di esplorare l’uso delle biotecnologie nel restauro
di pitture murali e stucchi che spesso mostrano una grande complessità per quanto
riguarda i materiali costitutivi e le condizioni conservative. I “metodi biologici” sono
stati confrontati con i metodi tradizionali, concentrandosi sul ripristino della coesione
degli strati superficiali (bioconsolidamento) e la rimozione dei solfati (biopulitura) che
si trovano spesso sugli affreschi come prodotti di decadimento. La sperimentazione si
è svolta nell’ambito di una tesi di laurea ed è stata suddivisa in due fasi: la prima, in
laboratorio, su campioni di intonaco dipinto e la seconda, in situ, sugli affreschi e gli
stucchi della chiesa di Santa Pudenziana in Roma, Italia. L’applicazione dei prodotti è




                                                                                                   CONSERVATION SCIENCE IN CULTURAL HERITAGE
stata seguita da una campagna di indagini volte a determinare l’efficacia, i vantaggi e
gli svantaggi di questi metodi rispetto a quelli convenzionali.




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