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Article

New Chemical Systems for the Removal of Calcareous Encrustations on Monumental Fountains: A Case Study of the Nymphaeum of Cerriglio

by
Claudia Squarciafico
1,2,*,
Giorgia Salatino
2,
Mauro Francesco La Russa
3,*,
Teresa Peluso
4,
Lorenzo Basile
1,
Fina Serena Barbagallo
1,
Monica Coppola
5 and
Andrea Macchia
1,2,4,*
1
Art Academy of Naples, Via Costantinopoli 107, 80138 Naples, Italy
2
YOCOCU, Youth in Conservation of Cultural Heritage, Via T. Tasso 108, 00185 Rome, Italy
3
DIBEST, University of Calabria, Via Pietro Bucci, 87036 Arcavacata, Italy
4
Artes Restauri e Servizi per l’Arte, Vico Lungo San Raffaele 16, 87036 Naples, Italy
5
Uffici Amministrativi, Largo Vescovado, 2, 00186 Massa Lubrense, Italy
*
Authors to whom correspondence should be addressed.
Heritage 2023, 6(9), 6358-6376; https://doi.org/10.3390/heritage6090333
Submission received: 1 August 2023 / Revised: 1 September 2023 / Accepted: 13 September 2023 / Published: 15 September 2023
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Versions Notes

Abstract

:
This study aims to compare the effects of some chemical agents on the removal of calcareous encrustations, which are characterized by the presence of both calcium and silicon. The experimentation was conducted during the conservation treatments of Cerriglio’s nymphaeum (Massa Lubrense, Naples, Italy). Tests were carried out in the laboratory on specimens and in situ to define the most efficient choice between several chelant agents, in the recovery of calcium and silicon, using ICP/OES and spectrocolorimetric and microscopic analyses.

1. Introduction

Calcareous stone materials exposed in outdoor environments are strongly affected by the presence of water due to the capacity to solubilize and to precipitate calcite [1]. Water can penetrate the porosity of calcareous stone and wash away calcite grains, leading to a higher level of decohesion in the stone [2,3]. Furthermore, soluble salts can migrate toward the stone’s surface, occluding its pores during water evaporation. The resulting calcium carbonate (CaCO3) and calcium sulfate dihydrate (CaSO4 2H2O) can crystallize as extra-thin crystals of calcite and gypsum, which act as new binders toward the grains, causing encrustations. The engine of this deterioration phenomenon is the presence of water, which, in combination with atmospheric pollutants, produces acid solutions [4].
As we know, calcium carbonate (calcite) is slightly soluble in water (0.014 g/L at 250 °C), but pH value variations caused by the presence of carbon dioxide increase the water’s capacity to dissolve it, leading to the formation of bicarbonate, as shown in the following reaction:
CaCO3 + H2O + CO2 => Ca(HCO3)2
This chemical balance is affected by temperature, pressure, and other factors and can be easily found in nature (it is responsible for the formation of stalactites, encrustations, etc.) [5]. The abiotic formation of carbonates consists of four key factors: (i) an increase in the calcium concentration, (ii) the presence of high inorganic carbon concentration, (iii) the “alkalinity engine”, which is activated with an increase in the water/seawater pH values, and (iv) the availability of nucleation sites [6,7]. Recently, several studies have demonstrated the role of microorganisms in the formation of calcareous concretions and encrustations both of alkaline and acid minerals [8,9,10,11].
Many different microorganisms have key roles in the formation of concretions through biological molecules (complex high-molecular-weight mixture of polymers excreted by microorganisms, proteins, enzymes, organic cofactors, organic acids, etc.) [7,8,9,10,11,12].
The formation of calcareous encrustations happens to be frequent in monumental fountains [13], where consistent deposits can develop due to the persistence of the previously cited factors. Those are generally characterized by high levels of compactness and thickness and can cover wide surfaces, erasing their chromatic and morphologic features.
Pure calcium carbonate is a white compound, which produces encrustations that are characterized by a white appearance. However, in nature, calcium carbonate encrustations commonly show various shades and colors due to the combination of salt with other ionic species, such as metals (Table 1). In the case of monumental fountains, metal ion contamination can be caused by the contact of the stone with metal elements or can be directly related to the characteristics of the water used in the fountain system. The table below lists the most common features of calcium carbonate encrustation, related to the nature of their impurities.
In addition to the presence of mineral impurities, other factors can influence the coloration of calcareous concretions, such as the structure of the crystal lattice (large crystals tend to be more colorful than micro crystals) and the presence of organic materials and contaminants [14]. The concretions grow very slowly with a variable growth speed that depends on many factors: the quantity of water, the level of saturation, the genetic mechanism (tubular concretions grow faster than crusts), the climate and morphology of the karst system, etc. Usually, the growth varies from a few microns per year (0.02 mm/year) to fractions of a millimeter (0.2) in standard conditions; instead, in thermal caves, there are way faster growths that can reach up to 100 mm/year [15].
To effectively and safely remove calcareous encrustations during restoration practices, mechanical, physical, and chemical cleaning methods are traditionally used [16].
For chemical cleaning, the treatment consists of using diluted acids or chelating agents applied with cellulose or other supporting agents, such as the salts of ethylenediaminetetraacetic acid (EDTA) [17,18,19,20].
For example, on the monumental Fountain of Neptune in Bologna, encrustations of carbonatic nature related to the recycling of chlorinated water are widely present and cover almost all of the stone surfaces. These encrustations have different thicknesses and are highly disfiguring for the monument since they strongly affect the legibility of surfaces [21].
From studies conducted on other fountains, such as the Trevi Fountain in Rome, it was possible to notice that the carbonatic encrustation, which incorporates pollution and atmospheric particulate, can show different macroscopic features. These differences have been explained as consequences of the various ways the water impacts the material in the fountain’s basin, particularly its trajectory, intensity, quantity, and flow, which affect the color, shape, thickness, and hardness of calcareous concretions [22].
This study starts with the encrustations that are present on the basal part of Cerriglio’s nymphaeum, characterized by the simultaneous presence of calcium and silicon compounds, to test the effectiveness of traditional and innovative chelant agents to remove the “calcareous” encrustations. The precipitation of silicon and calcium compounds can induce the formation of hydraulic compounds that are more stable than CaCO3 [23,24,25,26].
This study analyzes the possibility of removing mixed calcium and silicon encrustations with both chemical agents that are commonly used in cultural heritage treatments—such as EDTA—and an innovative chelating agent: N-acetyl-L-glutamic acid (GLDA). GLDA seems to be an ideal chelating agent for its biodegradability and power over a wide pH range. Their contribution to clay dissolution, in comparison with EDTA and N-(2-hydroxyethyl) ethylenediamine-N,N′,N′-triacetic acid (HEDTA), has been the object of recent studies [27,28,29].
However, Ethylenediaminetetraacetic acid (EDTA) is widely used in several applications, and its persistence in aquatic systems is leading to serious environmental consequences. GLDA salts are biodegradable candidates that can replace EDTA [30,31]. They showed a strong capability of chelating calcium ions at pH values in a certain range [32,33].
In the experimentation, EDTA and GLDA salts were tested with several pHs to define the best interaction specifically for the studied system, since the equilibria between the chelating agents and the metal ions are sensitive to pH changes [34].
Moreover, pH changes influence the ability of silicon to dissolve. At pH 11, the amorphous structures characterized by tetrahedral silicon are rapidly and completely dissolved [35,36].

Description of the Nymphaeum of Cerriglio

The Nymphaeum of Massa Lubrense is located inside a building called Rachione, which belonged to the De Martino family, mentioned from 1585 [37]. Over the years, the palace has been referred to as “Cerriglio” [38] by the local inhabitants. The fountain’s dating cannot be confirmed because of the lack of sources, but thanks to the engraving figuring satyrs, we can place it in the seventeenth century (Figure 1).
The fountain consists of a main body in which in the center, one can see a staircase made with mortar and marble slabs. Under those, some lead sheets are arranged, perhaps to create water effects.
The structure rests on five feet made of mortar and local stone similar to tuff (it is assumed that the central foot was added later), with a grey coloration. The fountain is inserted in a semicircular niche with a basin. The interior of the niche is decorated with a regular pattern formed by alternating surfaces and small marble fragments embedded in a colored mortar; the upper part is adorned with blue plaster decorated with white dots. The decorations are outlined by dark-colored stone (lapillus), and inverted bivalves are arranged to form roses between them.
The outdoor bath is made of fresco (white background) with a geometric dark blue decoration (Figure 2.). The pattern is divided into three modules, each containing a circle divided into four segments, with two shades of white and two shades of blue; in the center of the “wheel”, another small circle is visible, which is also divided into four segments with reverse colors. The circles are enclosed in a frame formed by a decoration composed of white and blue inverted squares on the top and a blue stripe on the bottom.

2. Materials and Methods

The first step of the research was to define the chemical composition of the calcareous encrustation and the pigments used in order to avoid possible interactions between the chelating agents selected to remove the encrustation and the metal chromophore. Figure 3 shows the chosen sampling area.
The samples were analyzed via Fourier-transform infrared spectroscopy in attenuated total reflectance mode (FT-IR ATR) performed with a Nicolet Summit FT-IR spectrometer equipped with the Everest™ Diamond ATR accessory (9ThermoFisher Scientific™), and a scanning electron microscope (SEM) (VEGA3-Tescam) coupled to an Inca 300 Energy Dispersive X-ray (EDS) microanalysis system was also used. The beam intensity was adapted to analyze non-conductive samples in a high vacuum environment.
Once the compositions of encrustations and the pigments used for the decoration were defined, the second phase of the study was the definition of the best treatment to remove yellow encrustations. Several water-based chelating agents commonly used in restoration treatments (EDTA disodium, EDTA tetrasodium, Ammonium Carbonate, Resin Ionex H+, and AB57) and additional chelating products derived from the industry (GLDA1 and GLDA2) were tested.
The table below (Table 2) shows the formulates used during the experimentation. Although the use of solutions with a pH < 5.5 on calcareous substrates of historical and artistic interest is traditionally not recommended in the conservation field, we decided to use disodium EDTA to lower the pH and to improve the effect on the chelation of calcium.

2.1. Laboratory Specimens

To determine the optimal chelating solutions, laboratory specimens were realized to simulate the stratigraphy found on the outdoor bath of Cerriglio’s fountain. This stratigraphy included the bath mortar, the decorative layer, and the encrustation. To emulate the bath mortar, the porosity and texture of the original mortar were examined through both macroscopic and microscopic observations. Additionally, the color was quantified using a spectrocolorimeter (3Nh Y3060). For the realization of these layers in the specimens, a blend of lime, sand, and finely ground local tuff was employed.
Several tests were conducted to establish the composition of the layer adjoining the encrustation, including considerations of the color, elemental composition, and porosity. The formulation most closely resembling the desired properties involved a mixture of 1 part slaked lime, 3 parts potassium silicate, and ½ part local tuff.
The replication of the stratigraphy was achieved within laboratory test tubes. The choice of these containers was driven by the necessity to operate within a controlled temperature bath (set at 25 °C) and to facilitate visual monitoring of the ongoing processes. The reproduced stratigraphy encompassed the following layers (as depicted in Figure 4):
0. Arriccio layer (in a 1:3 ratio) comprising 1 part pure white lime (Lafarge, CTS), 2 parts pozzolana, and 1 part local tuff;
1. Intonachino layer (in a 1:2 ratio) composed of 1 part lime and 2 parts local tuff;
2. Color layer fashioned using cobalt blue pigment and slaked lime;
3. Encrustation layer.
In the specimens, the decorative layer was realized using cobalt blue, although it is not the pigment used in the ornamentation of the outdoor batch. The choice of cobalt blue was made to assess the interaction between the chelating solutions and the decorative layer using the same analytical technique used for the determination of calcium and silicon, without introducing pigments such as ultramarine blue, which is characterized in silicon by the presence in the molecule.
The specimens were left to carbonate for three months, verifying the possible presence of basicity in the environment using the phenolphthalein test. After the complete carbonation of the samples, removal tests were performed by applying 5 ml of all the different extracting solutions to the specimens using the following contact times: 30, 90, 180, 480, 1020, 1200, and 1380 min.
At the end of every contact time, the solutions were extracted with a syringe calibrated at 0.5 mL. The samples obtained were diluted in demineralized water, in a ratio of 1:5, and were analyzed via Inductively Coupled Plasma—Optical Emission Spectroscopy (ICP-OES) (Thermo Scientific ICAP 6000) to determine their ability to recover calcium and silicon, and consequentially, to solubilize the encrustation.
The table below reports the weights of single layers, which are useful to understand the variance particularly related to the encrustation layer. A high coefficient of variance was induced to normalize the ICP/OES results with the weight of encrustation for a single tube (Table 3).

2.2. In Situ Tests

The chelating agents were also tested in situ, to compare the results obtained in the laboratory, by applying the chelating solutions with methylcellulose poultice (5 mL of solution in 25 g of supporting agent) with a contact time of 1020 min on 5 × 5 cm nearby areas.
To verify the treatment’s efficacy, portable efficacy optical microscopy (Dinolite AM411-FVW) and a spectrocolorimeter were used. Spectrocolorimetric analysis was carried out using a Y3060 3 nh spectrophotometer with an 8 mm aperture lens and three Xenon light bulbs that grant simultaneous acquisition in SCI (specular component included) mode. Spectra were acquired in the visible region (400–700 nm), and the color was defined using the CIELab color space coordinates L*, a*, and b*. An average of five measures for each tested zone were collected. For each zone, ΔL*, Δa*, Δb*, and ΔE* were calculated while taking into account the parameters L*, a*, and b* before the treatments and after the cleaning processes using the following formulas:
Δa* = a*2 − a*1
Δb* = b*2 − b*1
ΔL* = L2 − L1
ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)2]½
where L*1, a*1, and b*1 are related to the measures before each cleaning treatment, and L*2, a*2, and b*2 are related to the measures after the cleaning treatment. The ΔE* parameter gives information about the total difference in the treated surface and the action for each tested chelating agent. A different color (ΔE*) > 5 can be detected by human eyes [39,40].
The simulation of surface color was obtained using color hex code.

3. Results

3.1. FTIR and SEM/EDS on Encrustation and Color of Decoration

The IR spectrum of the encrustation (Figure 5) is characterized by main peaks at 1424, 1002, 871, and 711 cm−1, which are related to plane bending and asymmetrical stretching vibration peaks of O-C-O (1424, 875, and 711 cm−1) and a Si-O bending vibration near 1002 cm−1 [41].
The elemental composition of the encrustation was defined by submitting a micro-sample to the SEM analysis.
The SEM images (Figure 6) allowed us to observe high homogeneity in the sample, mainly consisting of calcium carbonate (identified by the molar ratio of calcium (Ca), carbon©, and oxygen (O)). Silica (Si), on the other hand, is related to aluminum (Al), calcium, and magnesium for the cations part, originating from the chemical composition of the fountain’s water. We also observed that the sample mainly consists of calcium carbonate and a component of calcium silico-aluminates (Table 4).
From the diagnostic investigations, we also concluded that the hardness of the encrustation was due to its hydraulic nature.
The spectrum (Figure 7) of the outdoor bath background shows the typical bands of calcite, 718, 875, and 1425 cm−1, corresponding to the out-of-plan bending and asymmetric elongation vibration bands of the O-C-O group with a low amount of silica (798 and 779 cm−1) [40].
The collected SEM images of the white background of Cerriglio’s outdoor bath, in retro-diffused electrons, do not show different contrasting elements in the various fragments constituting the sample. The EDS analysis shows the presence of significant elements such as oxygen and calcium that allow for the hypothesis of the presence of calcium carbonate. The low iron (Fe) content is related to the presence of silica (Si) and Fe that reveals the presence of iron silicoaluminate (Figure 8 and Table 5).
The SEM image of the dark blue decoration highlights the presence of lighter contrast elements on the sample’s surface (Figure 9 and Table 6). In particular, the EDS analysis allowed us to define this contrast due to the presence of iron, which appears to be the only chromophore element that can define a dark coloring of the sample’s surface. The presence of sodium (Na) in relationship with aluminum (Al), sulfur (S), and silicon allowed us to hypothesize the use of ultramarine blue as a pigment.
The sulfur content found in the back is related to the presence of calcium sulfate, and its formation is probably connected to degradation processes induced by the water source.

3.2. Test on Lab Specimens

The effectiveness of the chelating solutions in removing encrustations was assessed through the analysis of calcium and silicon ppm recovery using ICP/OES on laboratory specimens. Figure 10 and Figure 11 present the calcium and silicon ppm values, standardized by the weight of each encrustation within their respective tubes. To establish the max concentration of calcium and silicon in the encrustation, 0.1 g of simulated encrustation was entirely dissolved via an acid treatment (0.5 M HCl + HNO3 for 1 h), resulting in the following maximum concentrations: calcium = 8000 ± 54 ppm; silicone = 25,000 ± 112 ppm.
The GLDA and EDTA solutions efficiently recovered calcium and silicon simultaneously compared to the other chelating agents that demonstrated low efficacy. After longer contact times, EDTA showed a greater chelating affinity for calcium ions than silicon. GLDA 1 demonstrated the same chelating efficacy for both of the ions, while GLDA 2 had an excellent chelating power on silicon compared to calcium. None of the tested solutions recovered the maximum concentrations of calcium and silicon.
The trends in the plot highlight the high efficacy of GLDA 1 to remove encrustations, but the high chelation of calcium represents a possible risk factor for cultural heritage calcareous stone and for pigments dispersed in a carbonatic matrix, so it is not recommended to let GLDA come in contact with the fountain’s surface.
After GLDA, the maximum chelating action for calcium was performed using disodium EDTA, followed by GLDA2, tetrasodium EDTA, the cationic resin (Ionex h+), ammonium carbonate, and finally, AB57.
Regarding silicon, significant chelating action was achieved, in order (after GLDA1 and GLDA2), by disodium EDTA, tetrasodium EDTA, ammonium carbonate, AB57, and IONEX H+.
The ICP/OES analysis performed on the treated laboratory specimens showed that the solutions of GLDA1 and GLDA2 solubilized the encrustation more successfully in comparison to the other substances. Only the GLDA1 solution, applied on the specimens with contact times ranging from 1020 to 1380 min, was able to recover a high ppm of silicon. This result is due to the high pH value of the chelating solution that leaches the silicate networks. The high pH value of GLDA 1 is excellent for the dissolution of calcium and for the hydrolysis of silicate networks. On the other hand, the pH value of GLDA2 favors the hydrolysis of silicate networks while reducing the chelating action against calcium ions. The NAEDTA solution acts mainly in calcium ion recovery. This result could be due to the low alkaline Ph of the solution.
Figure 12 shows the result of encrustation cleaning on the specimens treated with the GLDA1 solution. It is possible to notice that the encrustation was almost eliminated, and the pigment did not undergo alterations.

3.3. In Situ Test

After the laboratory tests, in situ applications were carried out directly on the fountain’s encrustation.
Table 7 shows the pictures collected for each area treated with the chelating solutions. The images are listed in ascending scale, from the least to the most satisfactory cleaning result. A strong difference can be noticed between the pictures collected before and after the cleaning treatments with the better performing chelating agents.
Based on the images, the solutions of deionized water, IONEX H+, and EDTA Na4 did not provide any recovery. In comparison, the solutions of AB57, (NH4)2HCO3, and EDTA Na2 produced some results. Finally, it is clear that the best cleaning efficacy was obtained from the GLDA 1 and GLDA 2 solutions.
Table 8 reports the colorimetric parameters acquired before and after the cleaning treatments.
The delta E that was calculated from the collected data (Table 8) allows us to observe a strong chromatic variation in the surfaces, which was obtained via the treatments with GLDA 1 and GLDA 2. After the application of these treatments, strong decreases in the a* and b* components were found, and the surface took on a greater luminosity. For GLDA 1, the L* parament increased from 83.37 to 95.46, while a* and b* decreased from 1.68 to −0.48 and from 8.88 to 2.66, respectively. A higher chromatic variation was obtained by GLDA2, where L* increased from 82.28 to 93.57, a* decreased from 2.12 to 0.23, and b* decreased from 10.34 to 1.34.
The treatments with the EDTA Na2, EDTA Na4, AB57, and (NH4)2HCO3 chelators led to a decrease in the yellow component, while the application of the water and IONEX H+. solutions did not lead to any significant variations.
The in situ results reflect the ones obtained in laboratory; the GLDA1 solution had better results than the other chelants.
By combining the laboratory and in situ test results, it can be seen that GLDA2 had the best performance. For this reason, all of the outdoor bath was treated with GLDA2 for three times with a contact time of 1020 min. The treatment successfully softened the yellow patina, maintaining a thin layer of encrustation near the surface, and allowing for a better sight of the basin’s decorations (Figure 13, Figure 14, Figure 15 and Figure 16).

4. Conclusions

This study focused on the possibility of using GLDA as a chelator in order to remove encrustation composed of both calcium and silicon located on the basin of Cerriglio’s nymphaeum. It was performed with a multidisciplinary approach, which consisted of a comparison between solutions that are commonly used in restoration procedures and others, both in the laboratory and in situ.
The chelating efficacy of EDTA was sufficient, but less than that of the solutions of GLDA1 and GLDA2.
The ICP-OES results show that GLDA1 chelates Ca more than GLDA2, representing a potential risk for the original substrates. For this reason, the least aggressive but most effective chelator was chosen.
Since there are no specific works in the literature about the treatment of encrustations with a mixed composition located on the plasters of monumental fountains, all of the decisions were thoughtfully carried out on this specific case.
These new chelators are still in an experimental phase; hence, their possible applications are still being tested. Future research could focus on applying GLDA2 on different materials on monumental fountains in order to provide restorers with a new green chelator for the removal of thick encrustations from various supports.

Author Contributions

Conceptualization, A.M.; methodology, A.M., F.S.B. and L.B.; validation, A.M. and C.S.; formal analysis, A.M.; investigation, C.S.; resources, C.S. and T.P.; data curation, A.M.; writing—original draft preparation, C.S.; writing—review and editing, A.M., G.S. and C.S.; visualization, A.M., G.S., C.S. and M.C.; supervision, A.M. and M.F.L.R.; project administration, A.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Not applicable.

Acknowledgments

This work was conceptualized and supported by Youth in Conservation of cultural Heritage (YOCOCU APS), Rome, IT.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The fountain before the restoration treatment.
Figure 1. The fountain before the restoration treatment.
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Figure 2. Details of yellow encrustation (a) and the dark blue decorations (b).
Figure 2. Details of yellow encrustation (a) and the dark blue decorations (b).
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Figure 3. Sampling for IR and SEM/EDS analysis.
Figure 3. Sampling for IR and SEM/EDS analysis.
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Figure 4. Specimens realized in laboratory: (a) Samples with arriccio, intonachino, and painted layer; (b) arriccio, intonachino, color, and encrustation.
Figure 4. Specimens realized in laboratory: (a) Samples with arriccio, intonachino, and painted layer; (b) arriccio, intonachino, color, and encrustation.
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Figure 5. FTIR spectrum of the encrustation sample.
Figure 5. FTIR spectrum of the encrustation sample.
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Figure 6. Image obtained via SEM-EDS analysis on encrustation.
Figure 6. Image obtained via SEM-EDS analysis on encrustation.
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Figure 7. IR spectrum of the white pigment sample.
Figure 7. IR spectrum of the white pigment sample.
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Figure 8. Image obtained via SEM-EDS analysis on white “background”.
Figure 8. Image obtained via SEM-EDS analysis on white “background”.
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Figure 9. Image obtained via SEM-EDS analysis on dark blue sample.
Figure 9. Image obtained via SEM-EDS analysis on dark blue sample.
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Figure 10. Ca (ppm) graph extracted from solutions. GLDA1 (light blue); Na2EDTA (green); GLDA2 (orange); Na4EDTA (yellow); Resin Ionex H+ (dark blue); AB57 (blue); (NH4)2HCO3 (grey).
Figure 10. Ca (ppm) graph extracted from solutions. GLDA1 (light blue); Na2EDTA (green); GLDA2 (orange); Na4EDTA (yellow); Resin Ionex H+ (dark blue); AB57 (blue); (NH4)2HCO3 (grey).
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Figure 11. Si (ppm) graph extracted from solutions. GLDA1 (blue); GLDA2 (orange); EDTA Na2 (green); EDTA Na4 (yellow); Ionex H+ resin (dark blue); AB57 (blue); (NH4)2HCO3 (grey).
Figure 11. Si (ppm) graph extracted from solutions. GLDA1 (blue); GLDA2 (orange); EDTA Na2 (green); EDTA Na4 (yellow); Ionex H+ resin (dark blue); AB57 (blue); (NH4)2HCO3 (grey).
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Figure 12. This picture shows the test tube before the application of the encrustation layer, with the layer, and after its removal.
Figure 12. This picture shows the test tube before the application of the encrustation layer, with the layer, and after its removal.
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Heritage 06 00333 g013
Figure 13. The images show the analysis realized on the basin’s surface with a portable optical microscope: (a) shows the operation; (b) shows, respectively, the left side (untreated) and the right side (treated).
Figure 13. The images show the analysis realized on the basin’s surface with a portable optical microscope: (a) shows the operation; (b) shows, respectively, the left side (untreated) and the right side (treated).
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Figure 14. The images show a portion of the tank decoration. (a) The portion before applying GLDA2 solution. (b) The same portion after the treatment.
Figure 14. The images show a portion of the tank decoration. (a) The portion before applying GLDA2 solution. (b) The same portion after the treatment.
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Figure 15. The basin with yellow encrustation before GLDA2 solution application.
Figure 15. The basin with yellow encrustation before GLDA2 solution application.
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Figure 16. The basin after GLDA2 solution application.
Figure 16. The basin after GLDA2 solution application.
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Table 1. The colors that are assumed in calcareous based on the impurities present.
Table 1. The colors that are assumed in calcareous based on the impurities present.
ImpurityColoring
IronYellow, brownish-red, and brown
ManganeseBlue/grey and black
LeadGrey
CopperGreen/blue
NickelDark yellow (calcite) and light green (aragonite)
ZincRed, brown, and black
ClayBrown
Table 2. Chelants used in the experimentation.
Table 2. Chelants used in the experimentation.
ChelatorCompositionConcentration
(Solvent: Water)		pHBrand of Reagents
EDTA Na2Ethylenediaminetetraacetic acid disodium salt5%4.5CTS
EDTA Na4Ethylenediaminetetraacetic acid tetrasodium salt 5%11CTS
(NH4)2HCO3Ammonium bicarbonate18%8CTS
IONEX H+Strong cation exchange resin with fine particle size15%9CTS
AB57(1) Water cc. 1000
(2) Ammonium bicarbonate gr. 30
(3) Sodium bicarbonate gr. 50
(4) E.D.T.A. (disodium salt) gr. 25
(5) Quaternary ammonium salt at 10% cc. 10
(6) Carboxymethylcellulose gr. 60		 9CTS
GLDA1Tetrasodium glutamate diacetate (GLDA) with a pH corrector5%11.8YOCOCU
GLDA2Tetrasodium glutamate diacetate (GLDA) with a pH corrector5%9.8YOCOCU
Deionized waterCommercial product
Table 3. Weights (g) of the single layers in specimens.
Table 3. Weights (g) of the single layers in specimens.
ArriccioIntonachinoPigmentEncrustation
Average4.282.200.134.29
SD0.230.120.021.30
Table 4. Encrustation’s chemical characterization.
Table 4. Encrustation’s chemical characterization.
SpectrumCOMgSiCa
Spectrum 18.155.51.01.733.6
Spectrum 29.655.01.11.933.3
Table 5. EDS results of “White background” sample.
Table 5. EDS results of “White background” sample.
SpectrumOAlSiCaFe
Spectrum 162.61.885.029.90.6
Spectrum 259.53.84.330.12.2
Table 6. EDS results for “Blue dark” sample.
Table 6. EDS results for “Blue dark” sample.
SpectrumCOMgAlSiSClNaCaFe
back23.854.0 1.01.90.9 0.318.0
front 56.32.46.316.21.60.91.013.71.5
back-66.5 3.02.3 28.3
Table 7. Portable optic microscope figures (20X).
Table 7. Portable optic microscope figures (20X).
ChelatorBefore ApplicationAfter Application
Deionized waterHeritage 06 00333 i001Heritage 06 00333 i002
IONEX H+Heritage 06 00333 i003Heritage 06 00333 i004
Na4EDTA Heritage 06 00333 i005Heritage 06 00333 i006
AB57Heritage 06 00333 i007Heritage 06 00333 i008
(NH4)2HCO3Heritage 06 00333 i009Heritage 06 00333 i010
Na2EDTA Heritage 06 00333 i011Heritage 06 00333 i012
GLDA1Heritage 06 00333 i013Heritage 06 00333 i014
GLDA2Heritage 06 00333 i015Heritage 06 00333 i016
Table 8. Colorimetric parameters of areas acquired before and after the cleaning treatments with different chelant solutions. SD related to all surfaces: SD(L*) < 1; SD(a*) < 0.5; SD(b*) < 1.1.
Table 8. Colorimetric parameters of areas acquired before and after the cleaning treatments with different chelant solutions. SD related to all surfaces: SD(L*) < 1; SD(a*) < 0.5; SD(b*) < 1.1.
Chelant SolutionColor SimulatorTreatmentL*a*b*
GLDA2#FFD7CBB9Before82.282.1210.34
#FFEEECEAAfter93.570.231.34
ΔE14.56
GLDA1#FFD8CEBFBefore83.371.688.88
#FFF3F2EDAfter95.46−0.482.66
ΔE13.77
EDTA Na2#FFD6CBB8Before82.012.4811.97
#FFE1DACAAfter87.150.538.47
ΔE6.52
EDTA Na4#FFD6CBB8Before82.181.6211.06
#FFE1DACAAfter87.150.538.47
ΔE5.71
Water#FFD8CAB6Before82.012.4811.97
#FFD6CBB8After82.181.6211.06
ΔE1.26
IONEX H+.#FFD7CBB9Before82.282.1210.34
#FFD8CEBFAfter83.371.688.88
ΔE1.87
AB57#FFD1C9BABefore81.251.098.44
#FFE1DACAAfter87.150.538.47
ΔE5.93
(NH4)2HCO3#FFD3CAB9Before81.71.49.45
#FFE0D8C8After86.640.869.04
ΔE4.99
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MDPI and ACS Style

Squarciafico, C.; Salatino, G.; La Russa, M.F.; Peluso, T.; Basile, L.; Barbagallo, F.S.; Coppola, M.; Macchia, A. New Chemical Systems for the Removal of Calcareous Encrustations on Monumental Fountains: A Case Study of the Nymphaeum of Cerriglio. Heritage 2023, 6, 6358-6376. https://doi.org/10.3390/heritage6090333

AMA Style

Squarciafico C, Salatino G, La Russa MF, Peluso T, Basile L, Barbagallo FS, Coppola M, Macchia A. New Chemical Systems for the Removal of Calcareous Encrustations on Monumental Fountains: A Case Study of the Nymphaeum of Cerriglio. Heritage. 2023; 6(9):6358-6376. https://doi.org/10.3390/heritage6090333

Chicago/Turabian Style

Squarciafico, Claudia, Giorgia Salatino, Mauro Francesco La Russa, Teresa Peluso, Lorenzo Basile, Fina Serena Barbagallo, Monica Coppola, and Andrea Macchia. 2023. "New Chemical Systems for the Removal of Calcareous Encrustations on Monumental Fountains: A Case Study of the Nymphaeum of Cerriglio" Heritage 6, no. 9: 6358-6376. https://doi.org/10.3390/heritage6090333

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