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Article

Use of the Volatile Binder Menthyl Lactate to Temporarily Consolidate and Transport the Earthquake-Damaged Wooden Crucifix of Santa Maria Argentea in Norcia

by
Vincenzo Amato
1,
Sara Bassi
1,* and
Renata Pintus
2,*
1
Conservation Department of Polychrome Wooden Sculptures, Opificio delle Pietre Dure, 50100 Florence, Italy
2
Opificio delle Pietre Dure, 50100 Florence, Italy
*
Authors to whom correspondence should be addressed.
Heritage 2025, 8(12), 522; https://doi.org/10.3390/heritage8120522
Submission received: 8 October 2025 / Revised: 21 November 2025 / Accepted: 28 November 2025 / Published: 11 December 2025
(This article belongs to the Special Issue History, Conservation and Restoration of Cultural Heritage)
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Abstract

This contribution illustrates the research focused on the process of securing and the transportation prior to the conservation treatment of a wooden Crucifix—severely damaged in 2016 during the earthquake of Central Italy—through the application of menthyl lactate. The preparatory and paint layers of the polychrome sculpture are extremely fragile due to decohesion issues and the presence of unstable cleavages and losses linked to severe thermo-hygrometric variations. Many scientific and application tests were carried out in the laboratory and then, later, on a fragment of the Crucifix in order to identify the volatile binder best-suited to this case study: menthyl lactate was selected among six binders as the most appropriate compound due to its effective consolidation, lower sublimation rate, negligible residue, and non-hazardousness. Lastly, a very specific transportation system was designed and realised to move the work, without further loss and damage, from the storage building where it was kept in Spoleto to the conservation department of the Opificio delle Pietre Dure in Florence. The volatile binder will continue to be locally applied to allow the mechanical cleaning, in order to remove the thick deposits of debris without damaging the colour. The conservation treatment will be carried out in the future, in parallel with further scientific tests.

1. Introduction

This work presents the process of securing and the transportation of the polychrome wooden Crucifix of the co-cathedral of Santa Maria Argentea in Norcia (Perugia), 1494, attributed to Giovanni Teutonico.
This study represents a key point among the research projects applied to the restoration and conservation of cultural heritage in emergency contexts, carried out by the Opificio delle Pietre Dure (OPD) of Florence as part of the Extended Partnership PNRR project “CHANGES: Cultural Heritage Active Innovation for Next-Gen Sustainable Society”, in particular among the activities of Spoke 6, “History, Conservation, and Restoration of Cultural Heritage” [1].
The long-lasting process of studying the sculpture and its state of conservation, as well as formulating a specific intervention methodology for such a delicate and complex case, began in 2018. In February of that year, the Crucifix was extracted from the ruins of the destroyed church and moved to the designated storage building in the locality of Santo Chiodo, near Spoleto (Perugia), where the OPD coordinates the conservation activities of thousands of artworks and artefacts damaged by the 2016 earthquakes, in collaboration with the Soprintendenza Archeologia, Belle Arti e Paesaggio dell’Umbria [2,3,4,5].
The research related to the Crucifix from Norcia continued from 2021 to 2024 with a PhD project in Technology, Conservation, and Restoration promoted by the Dipartimento di Storia delle Arti e dello Spettacolo of the Università degli Studi di Firenze; it was supported by the OPD as part of the main line of research within the CHANGES project on the use of green materials and VBM in emergency situations. The study focused on investigating the characteristics and possible applications of sublimating organic compounds with binding properties, in order to protect, stabilise, and temporarily consolidate the preparatory and paint layers of polychrome wooden sculptures and artefacts [6]. Another Crucifix attributed to the Giovanni Teutonico’s workshop from the church of Madonna Addolorata in Norcia (Perugia) was studied and partially restored during a Master’s degree thesis at the OPD Scuola di Alta Formazione e Studio in 2020–2021. The sculpture had also been damaged by the 2016 earthquake; in particular, the right arm had been buried under rubble for a long period of time, leaving it in a very poor state of conservation. On that occasion, an early research on volatile binders began: it was aimed to temporarily consolidate the degraded materials for allowing the removal of debris and then the adhesion of the preparatory and paint layers [7,8].
This work is just the first step of our research, which will be from now on properly dedicated to the conservation treatment of the Crucifix.
The sculpture, related to the last phase of the artistic production of Giovanni Teutonico—commissioned in 1494—was positioned on the Crucifix chapel altar, along the left aisle of the church, as shown in Figure 1. Carved in the round and life-size (dimensions: 174 × 174 cm), the work reflects the formal canons that make it a point of intersection between the International Gothic—with its realistic anatomical features and profound expressionist pathos—and the Italian Renaissance language, revealed in the frontal and symmetrical arrangement of the figure and the observance of bodily proportions. It was made by using several lime-wood elements, assembled with hide glue and wooden pegs, then carved, covered with a ground of gesso and animal glue, and finally painted. The high quality of the Crucifix is not only due to the refinement of the carving, but also to the richness of realistic and dramatic details, such as the locks of hair made of curled metal wires and vegetable fibres, the eyelashes and the beard hair made using copper wires, the application of multiple vegetable cords all over the preparatory layer to simulate the veins under the skin, and the presence of an articulated mechanism in the head to move the tongue. This last peculiarity is typical of the so-called “speaking Crucifixes”, traditionally used during the paraliturgical Catholic ceremonies on Good Friday since the 15th century [9].
On 30 October 2016, an earthquake measuring 6.5 on the Richter scale with its epicentre between the towns of Norcia and Preci caused the collapse of the roof and the upper part of the facade of the co-cathedral of Santa Maria Argentea, as shown in Figure 2.
The collapse of the ceiling caused the Crucifix to detach from the cross and fall to the ground. The violent impact brought about serious structural damage and fragmented the sculpture into numerous pieces, with consequent deformation of the wood fibres. In addition to that, the preparatory and paint layers were also damaged, including scratches, abrasions, losses, surface deformations, and cleavage from the wooden substrate. Immediately after the collapse, the instability of the building prevented the timely recovery of the sculpture fragments, which could only be extracted safely between 14 and 16 February 2018, as can be seen in Figure 3. During the fifteen months under the rubble, the Crucifix was subjected to intense and constant exposure to atmospheric agents (including snow during the two cold winters), which increased the problems of internal cohesion within the layers and aggravated their washout and lifting, causing a general and severe embrittlement of the constituent materials. Moreover, much of the painted surface was covered with thick, compact concretions of debris. When the pieces were rescued by the firefighters and moved to the storage building in Spoleto, the wood was completely soaked in water, and the paint layer was swollen.
Over the following five months—during which hundreds of artworks continued to be rescued from all damaged buildings in the region—keeping the sculpture in a well-ventilated area accelerated the drying of the fragments and reduced the proliferation of biodeteriogenic agents, but unfortunately also caused a significant shrinkage of the wood, as well as the development of new liftings and losses of the already severely detached preparatory and paint layers, as illustrated in Figure 4.
The need of handling the fragments of the Crucifix and moving them from the storage building in Santo Chiodo to the OPD Department of polychrome wooden sculptures in Florence—where the long and complex restoration treatment would be carried out in the future—was the starting point for the design of a specific system to secure the unstable preparatory and paint layers, and to temporary consolidate and lock the flakes that had already fallen in order to prevent further material loss. To achieve this, it was decided to avoid using the adhesives typically applied in such situations (i.e., animal or vegetable glue and wax as naturals, acrylic or vinyl resins as synthetics): in fact, by performing a permanent consolidation or a traditional facing, these adhesives would have penetrated under the cleavages and into the porosity of the materials, fixing the debris to the paint layer even more firmly, with unwanted irreversible consequences and further deterioration of the artwork. The solution found ensured maximum respect for the constituent materials, enabled a gradual approach during every phase, is completely reversible, and meets any criteria for retractability: a volatile binder was selected and applied, allowing the fragments to be temporarily—and not permanently—consolidated during transportation thanks to its capacity to sublimate, that is to change directly from a solid to a gaseous state, without leaving any residue. Therefore, after an initial testing phase based on the specific needs of the Crucifix, the volatile organic compound chosen was menthyl lactate (MNT_LAT), whose use as a temporary consolidating agent for unstable, highly decohesive paint films has not yet been documented. At the same time, other solutions were adopted to reduce oscillations and vibrations during transportation: thanks to the latest 3D scanning technologies, a system of “blocks” and “masks” was designed and 3D-printed to hold the fragments of the sculpture in place, preventing them from moving, sliding, or rotating. The sculpture was then placed in a double crate, internally cushioned with spring-loaded tie-rods. Finally, a customised fume hood was installed in the OPD Laboratory to contain the consolidated fragments and facilitate the sublimation of MNT_LAT, in conditions that are safe for the conservators too. These measures allowed the sculpture to be moved safely, without further detachments or losses of ground and colour.

2. Materials and Methods

The first phase of the project, which will be followed later on the conservation treatment of the Crucifix, was focused on the study of volatile binding media (VBM). They are cyclic organic compounds with adhesive and cohesive properties, which, at room temperature, look like waxy solids capable of sublimating due to their high vapour pressure. VBM were introduced as materials for the preservation of cultural heritage in 1995, thanks to the studies by the German conservator Hans-Michael Hangleiter and chemists Elisabeth Jägers and Erhard Jägers on cyclododecane (CDD), camphene (CNF), and L-menthol (MNT) [10]. Over the years, their high reversibility and versatility of application have ensured their widespread use in various fields of conservation: they are mainly used as temporary consolidating agents or adhesives, but also as surface protectants, water repellents, and provisional supports for fragmented artefacts made of various materials. The most widely used and documented since the late 1990s is undoubtedly CDD. Our research originated from the need to find one or more VBM capable of replacing CDD, as it was not commercially available at that time due to the closure in 2020 of the manufacturing laboratory Ephemeral GmbH in Otzberg (Germany), where Hangleiter himself was producing it since 2013. The product also had to be suitable for use on Giovanni Teutonico’s Crucifix. Thus, a testing project was set up to analyse the physical and chemical properties of five VBM in addition to CDD: cyclododecanol (CDOL), cyclododecanone (CDON), camphene (CNF), L-menthol (MNT), and L-menthyl lactate (MNT_LAT). Table 1 shows the chemical structural formulas of the six tested VBM, while Figure 5 illustrates their solid state at room temperature.
  • Cyclododecane is a saturated cycloalkane that looks like a semi-transparent, waxy crystalline solid with a slight mouldy smell at room temperature. It is completely non-polar, water-repellent, and soluble only in hydrocarbon solvents. It is mainly used as a reaction intermediate for the synthesis of polyamides, polyesters, and varnishes.
    In archaeological excavations, CDD is used during block lifting and packaging operations, as well as a consolidating, coating, and releasing agent during casting for the reproduction of fragments. On clay and ceramic artefacts, it is used as a protective agent during the desalination process of fragile objects with delicate, water-sensitive painted surfaces. It is also used for protection, water repellency, temporary consolidation and fixing on stones, wall paintings, easel paintings, textiles, and paper materials [6,7,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42]. Spray CDD can be applied to create a uniform opaque layer on surfaces to be scanned for the acquisition of 3D digital models [43].
  • Both cyclododecanol and cyclododecanone have a similar structure to CDD: the former has a hydroxyl group (-OH), while the latter has a carbonyl group (=O). Like CDD, they are both used in the synthesis of polyamides, polyesters, and varnishes.
    Their use for conservation was not previously documented [6,38,41].
  • Camphene is a natural monoterpene found in the essential oils of numerous plant species (especially conifers). At room temperature, it looks like a semi-transparent, waxy solid with a pungent, refreshing smell similar to camphor. It is soluble in both non-polar and polar solvents and is used in the synthesis of perfumes, lacquers, and insecticides, as plasticiser for resins, and as a substitute for camphor.
    CNF was previously tested on wall paintings, archaeological artefacts, ceramics, paper and other cellulosic materials [6,7,10,29,36,38,41,42].
  • L-menthol is a cyclic monoterpene, the main component of peppermint oil and essential oils from other mint species. At room temperature, it looks like a transparent, waxy, crystalline solid with needle-like crystals and a pungent, refreshing minty smell. It is soluble in both non-polar and polar solvents, and is used as a flavouring agent or fragrance in food, cosmetics, medicine, and chemicals.
    It was introduced as a consolidating agent for wall paintings, and is also used on archaeological artefacts, cellulosic materials, ceramics, and polychrome surfaces [6,7,10,36,38,41,42,44,45,46,47,48,49,50,51,52,53].
  • L-menthyl lactate is an ester of menthol and lactic acid. At room temperature, it looks like a semi-transparent, waxy solid with small needle-like crystals and a more fruity and less pungent minty smell than MNT. It is soluble in both polar and non-polar organic solvents and is used as a flavouring agent in food and cosmetics [6]. As of today, the only documented use in the field of conservation is in eutectic mixtures with menthol as consolidants for archeological objects [46] or as temporary screen coating on cellulosic materials [42].
In order to be applied to the surface of the artworks, VBM must be converted into liquid form; this change in state can be achieved either by heat, thanks to their thermoplastic properties, or by solvents. Therefore, three different application methods were defined for each material: melted, in solution with drop application, and in solution with spray application.
The six VBM were melted using a hot spatula CTS mod. Artist III, fitted with a special tip shaped like a small crucible; this allowed for controlled and precise application, setting the treatment temperature according to the melting point of the different compounds. For the two applications in solution, saturated solutions of each VBM were prepared (T = 25 ± 1 °C), dissolving each volatile binder in three of the most commonly used solvents in conservation: cyclohexane (Sigma-Aldrich, Merck KGaA, St. Louis, MO, USA) for hydrocarbons, ethanol for alcohols, and acetone (both ethanol and acetone: Carlo Erba Reagents S.r.l., Milan, Italy) for ketones. They were chosen in order to work with the maximum quantity of VBM in solution. Each solution was dripped using laboratory micropipettes Labsystems mod. Finnpipette 10–100 μL and sprayed by an airbrush Fengda mod. FE–135K and compressor Airgoo mod. AG–320 (P ≅ 1 bar; distance from the surface ≅ 5 cm).
VBM were applied to glass slides, and the morphology of the crystalline films was observed and photographed under a stereomicroscope Leica M205C with reflected light (LED light source and magnification up to 160×). The crystalline structure depends on the ratio between the nucleation rate (formation of crystallisation nuclei) and the crystal accretion rate: if the former prevails over the latter, smaller crystals are obtained and the solid has a structure more similar to the amorphous state; conversely, if the accretion rate exceeds the nucleation rate, a few larger crystals are formed, and the solid takes on a structure more similar to that of a single crystal. It was observed that the melted compounds form compact, hard, and resistant crystalline films on the surface, characterised by small crystals that are very close together. This type of solidification occurs because there is a sudden decrease in temperature between the hot melted products and the cold surface of the glass slides; therefore, the crystals do not have time to expand. Crystalline films generated from drop-applied solutions consist of crystals of variable sizes, depending on the concentration of VBM and the volatility of the solvent; in general, they are less resistant and less hard, as both the size of each crystal and the distance between them increase. Lastly, spray-applied VBM solutions are much softer and more fragile, as they consist largely of very small crystals, which already solidify during propulsion and deposit in multiple layers on the surface without forming actual and compact crystalline films. Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10 show the difference between the crystalline films of each volatile binder depending on the application method. The only exception is CNF in solution, as can be seen in Figure 11: regardless of the application method, it does not crystallise because it forms azeotropic mixtures, which are unable to solidify at room temperature before sublimation.
The sublimation rate was then estimated by measuring the weight variation in the samples at regular intervals on an analytical balance Kern mod. ARJ 220–4M; the test was performed in an insulated box at a controlled temperature of 25 ± 1 °C to minimise the impact of environmental factors (temperature, pressure, ventilation). In this way, the sublimation rate was mainly influenced by the application method, the quantity of volatile binder present in each solution and the evaporation rate of each solvent. These same three parameters also determined the variation in size of the crystals formed, their compactness, and the area of the exposed surface.
Melted VBM have more compact crystalline films, so they sublimate more slowly than those in saturated solution. Among VBM in saturated solutions, spray-applied ones sublimate faster because the crystals are smaller and part of the solvent already evaporates during propulsion. The collected data were processed into linear graphs, where the slope represents the sublimation rate (mg/h), as illustrated in Figure 12. For melted VBM, it is possible to compare the linear graphs, as exactly the same amount of material was applied to each glass slide; however, this is not possible for saturated solutions, where the concentration of VBM varies according to their solubility parameters. Comparing the data, we can see that CDD and MNT have similar sublimation rates, as do CDON and MNT_LAT. In contrast, CNF sublimates very quickly, while the sublimation of CDOL is so slow that it was not detected. The measured sublimation rates are shown in Table 2, which also summarizes the main physical and chemical properties of each volatile binder, as reported on PubChem website and in the relevant technical and safety data sheets [54,55,56,57,58,59].
A fundamental element for the application of VBM on cultural heritage is their ability to leave a negligible amount of residue on the treated surface. Such residues are essentially due to a minimal presence of impurities, which could derive from the following: industrial production processes; chemical transformations of molecules; possible chemical interactions with the substrate on which they are applied. The release of residues is an extremely negative factor (if not entirely inhibiting) during conservation work. In the case of VMB, the aim of this research was precisely to find consolidating substances that, after application, did not require any further chemical or mechanical removal, thanks to their ability to sublimate completely. To this end, a test was carried out to measure the quantity of any residues after complete sublimation. Only melted VBM (except CDOL, which has proven to be non-volatile) were analysed to avoid possible interference from solvents and operate with volatile binders at maximum concentration. The VBM samples applied to the glass slides were weighed with an analytical balance Mettler Toledo mod. XRS105DU at the time of crystallisation (W0) and after complete sublimation (W1). The percentage of residues released by each VBM was calculated by determining the ratio between the initial and final weights (W1 ÷ W0 × 100). The residues of CDD, MNT, and MNT_LAT are fairly negligible and transparent (0,7%), while CNF and CDON release detectable quantities of yellowish residual substances (≥3,5%), as shown in Table 2. Furthermore, while the residues of CDD, MNT and MNT-LAT look transparent, CNF and CDON are yellowish.
In order to evaluate the consolidating power of VBM, their capacity of penetration was analysed. Mock-ups were created with porosity and cohesion characteristics similar to those of a degraded generic preparatory layer. The ambient temperature was stabilised at 25 ± 1 °C. Graduated cylinders (diameter = 1,5 cm) were filled with Bologna gesso (hydrate calcium sulphate) without any binder to simulate decohesion. To the upper surface of the cylinders, 2,0 mL of each volatile binder was applied, melted and in saturated solutions, both dripped and sprayed. After 24 h, the penetration depth was measured with a calliper and the volume of gesso affected was estimated, as illustrated in Figure 13. CNF and CDON were excluded due to the excessive release of non-volatile residues resulting from the previous test. The crystallisation of melted VBM occurs very quickly on the surface, due to the sudden decrease in temperature between the melted substance and that of the gesso and the environment. For this reason, the degree of penetration is low. More specifically, CDD and CDOL crystallise more rapidly and more superficially than MNT and MNT-LAT, as their melting points are much higher than the temperature of the application surface (with rapid cooling, the compounds solidify more quickly and are unable to penetrate deeply). The degree of penetration of the drop-applied saturated solutions depends on the quantity of volatile binder present in the solution and the volatility of the solvent. Finally, the spray-applied saturated solutions did not penetrate the mock-ups because the dissolved volatile binders accumulated on the surface as small semi-solid crystalline flakes. Table 3 summarizes the different penetrated volumes.
It is important to emphasise that the results of this penetration test must be interpreted in light of its empirical nature. Mock-ups are not perfectly comparable to real situations, as the presence of the plastic cylinder inhibits contact with the air, thereby slowing down both the crystallisation and sublimation of VBM. Furthermore, it is not possible to accurately measure the depth of penetration of VBM into the innermost bulk of the mock-ups, as only their presence on the cylinder walls is detected. However, it is still possible to make some observations based on a comparison of the results obtained, with a view to applying VBM on brittle preparatory and paint layers.

3. Results

The results of the tests made it possible to select the VBM with the best properties and define the most suitable application methods for this case study of the Crucifix of Santa Maria Argentea.
Among the five melted compounds, the following were excluded: CDOL because it is non-volatile; CNF because it forms a film that is too soft, has too-rapid sublimation times, and leaves a high percentage of non-volatile residues after sublimation (3,5%); CDON because it leaves a very high amount of non-volatile residual substances (11,4%, the highest percentage of all the materials tested). On the other hand, both MNT and MNT_LAT proved suitable for application testing.
From the set of saturated VBM solutions with drop application, those containing CNF were discarded because the binder did not crystallise after the evaporation of any of the three solvents, as were those containing CDON due to the excessive release of non-volatile residues; CDOL solutions were not chosen either, because the crystalline films were not compact enough, with crystals too small and sparse to ensure a good consolidation.
The spray application method was discarded for all the solutions, as all VBM form crystals that are not very compact and sufficiently resistant to mechanical stress; furthermore, the crystalline films only form on the surface, without penetrating the substrate.
In light of all these results, MNT and MNT_LAT—whether applied as melted or dripped saturated solutions—passed all the tests. All applications were carried out in accordance with the safety instructions provided in each product data sheet: nitrile gloves and face masks with appropriate filters were worn, and all operations were accomplished under a portable fume hood.
Before applying any of the compounds to the entire Crucifix, application tests were carried out on the fragment of the right leg. MNT and MNT_LAT were injected via syringe, both on the surface and under the cleavages. The saturated solutions of the two VBM crystallised too slowly and formed crystalline films that were not compact enough, so they could not appropriately consolidate the layers (the solubility of cyclohexane, ethanol, and acetone on the paint layers had been tested beforehand). Moreover, all the attempts to perform multiple applications in the same area were unsuccessful, as the addition of solvent caused the crystalline film that had already formed to redissolve, preventing the stratification, and not filling the voids between the wood and the preparation. On the contrary, both the melted VBM formed compact and resistant crystalline films, with excellent consolidating properties. Their low viscosity allows for easy transmission via syringe, even in the most difficult-to-reach areas. Consecutive applications allow the crystals to stratify and fill the empty spaces under the cleavages. VBM were melted in special wax heaters LaborPro mod. 105 and mod. 106 with adjustable temperature; they were then applied using syringes with blunt needles of different curvatures and gauge measures, as shown in Figure 14. This method made it possible to quickly liquefy large amounts of VBM and distribute them over wide areas of the sculpture. Given that the two VBM tested showed comparable consolidating capability, MNT_LAT was selected because it guarantees a longer-lasting action, thanks to its lower sublimation rate (about ten times lower than MNT); in addition, its non-hazardousness and less pungent smell help during the operating phase [58,59].
The results obtained from the analytical and application tests enabled the selection of MNT_LAT and the definition of the most suitable methodology for this case study. Therefore, a special area for the temporary consolidation of the Crucifix was set up inside the storage building in Santo Chiodo. The smallest fragments of the sculpture, consolidated with melted MNT_LAT applied via syringe, were placed in rigid plastic boxes, internally upholstered with expanded polyethylene (Ethafoam® supplied by Isopad, Gruppo Sogimi, Prato, Italy) and cushioned with acid-free tissue paper. At the same time, the consolidation was also carried out on the larger fragments placed on the pallet, as can be seen in Figure 15. The treatment was accomplished by four conservators, and took four days of work and approximately 3 kg of MNT_LAT.
In parallel with the study of VBM for the consolidation of the preparatory and paint layers of the Crucifix, its transportation and subsequent storage in the OPD Department of polychrome wooden sculptures were planned. In particular, the larger fragments of the sculpture were the most complicated: after being extracted from the rubble in 2018, they had been placed on a wooden pallet and had not been moved since due to their extreme fragility. In order not to move them even after the consolidation treatment, a specific locking system was designed. It was essential to keep the pieces in their position and avoid their separation from the smallest fragments of paint that had fallen off on the pallet, aiming to reattach them to the wooden support in their exact original place. It was decided to use 3D technology, which has been applied for years in heritage conservation with excellent results, including the transport and packaging of fragile and fragmented works [60,61,62,63,64,65,66,67,68,69]. Therefore, the entire surface was 3D scanned and a digital model was created. For each fragment (the torso, the left leg, and both arms), four areas without ground and colour were identified as ideal support surfaces for “blocks”, as it was unattainable to apply pressure on painted surfaces without risking damage. These were made with wooden pieces screwed to the pallet, to the ends of which were fixed 3D “masks” printed using the digital model, as illustrated in Figure 16. Each block was positioned opposite another one, so as to contrast any possible rotational or translational movement of the fragment during transportation. Each one of the twelve masks was 3D printed with a special stereolithographic resin, with excellent detail reproduction accuracy and a low elastic modulus (this allows it to break in the event of mechanical shock, rather than exerting excessive pressure on the fragment of the sculpture); the resin was selected after careful comparison of those available on the market, in order to meet the above requirements [70,71,72,73,74]. They were coated with a double cushioning layer of the synthetic rubber foam Aerstop® supplied by Isopad, Gruppo Sogimi, Prato, Italy. Finally, some wooden crossbeams were screwed around the pallet to create a “cage” around the Crucifix, as can be seen in Figure 17.
Figure 18 shows how this protective structure was then placed in a double crate made with an internal system of spring-loaded tie-rods, which connected the two wooden crates. This system allowed the sculpture to travel suspended during the journey by truck, in order to absorb and cushion any mechanical shock.
Finally, after the removal from the crate in the OPD Laboratory, the fragments—still placed on the pallet—and the boxes with the smaller ones were put in a customised walk-in fume hood, as shown in Figure 19, in order to keep them safe and to speed up the sublimation of MNT_LAT.

4. Discussion and Conclusions

This case study confirmed the importance of VBM for the conservation of cultural heritage, with particular reference to their consolidating properties in the process of securing works damaged by catastrophic events. Analytical tests provided fundamental results for characterising compounds with these properties: it was possible to discard some (CDOL, CDON, and CNF) and select others (MNT and MNT_LAT) in addition to CDD, which has since become commercially available again. In particular, the introduction of MNT_LAT and its first successful application in the field of conservation represent an excellent innovation. The range of possibilities available to conservators is therefore broader, and further research into these compounds is encouraged.
The tenacity of MNT_LAT’s consolidating power was definitively proved when the crate was opened. At that point, it was discovered that the “block” holding the Crucifix’s neck had broken, probably due to a particularly strong vibration during transportation by truck. The break caused the torso to rotate slightly and shift from its original position. Nevertheless, the presence of the solid film of MNT_LAT on the surface and beneath the cleavages ensured the stability of the preparatory and paint layers, preventing them from collapsing or falling off. Only some debris from the hollow interior of the torso, where the binder had not been applied, detached.
The coordinated system of temporary consolidation with melted MNT_LAT, the creation of blocks with 3D printed masks, and the double crate with spring-loaded tie-rods has made it possible to move the sculpture safely, without the need to handle the most fragile fragments, and prevented the detachment and loss of further paint material. The positioning in the fume hood is facilitating and speeding up the sublimation of MNT_LAT, in conditions that are safe for the conservators too, allowing them to begin the next steps of this complex restoration project. The conservation treatment on Giovanni Teutonico’s Crucifix will be carried out in the future in parallel with further scientific tests (crystallographic studies, possible consequences of crystallisation on the porosity of the substrate) and application tests on different materials (paintings on canvas, murals, paper, etc.).

Author Contributions

Conceptualization, V.A. and S.B.; methodology, V.A. and S.B.; formal analysis, V.A. and S.B.; investigation, V.A.; resources, V.A., S.B. and R.P.; writing—original draft preparation, V.A. and S.B.; writing—review and editing, V.A., S.B. and R.P.; visualization, V.A. and S.B.; supervision, V.A., S.B. and R.P.; project administration, S.B. and R.P.; funding acquisition, R.P. All authors have read and agreed to the published version of the manuscript.

Funding

This project is funded by the European Union—Next Generation EU under the National Recovery and Resilience Plan (PNRR)—Mission 4 Education and Research—Component 2 From Research to Business—Investment 1.3, Notice D.D. 341 of 15 March 2022, entitled: Cultural Heritage Active Innovation for Sustainable Society, proposal code PE0000020—CUP F53C22000690006, duration until 28 February 2026.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

The authors gratefully acknowledge conservators Arianna Acciai and Giulia Ciabattini for their hard work and professionalism during the consolidating and packaging operations in Santo Chiodo; conservator Mattia Mercante for 3D scanning and printing; art historians Riccardo Gennaioli and Renata Pintus (OPD) as coordinators of the project; conservation scientist Andrea Cagnini and all the colleagues of the OPD Scientific Laboratory for the analysis; conservators Luciano Ricciardi e Andrea Santacesaria (OPD) for the anoxic treatment; conservator Oriana Sartiani (OPD) for coordinating relations with SABAP Umbria and Centro Operativo Beni Culturali of Santo Chiodo; conservator Marina Ginanni (OPD) for sharing photographic documentation; all the colleagues of the OPD Department of polychrome wooden sculptures; OPD Purchasing, Technical and Administrative Offices; conservator Nicola Bruni and art historians Giovanni Luca Delogu, Elena Marchionni, and Giulia Spina (SABAP Umbria and Centro Operativo Beni Culturali of Santo Chiodo) for their constant availability and support; all the freelance conservators operating in Santo Chiodo for their kind collaboration; conservators Roberto Bonaiuti (OPD), Giulia Basilissi (Museo Archeologico Nazionale, Florence), and Flavia Puoti (Gallerie degli Uffizi, Florence) for sharing their experiences in valuable discussions; Atelier Cultura di Marzia Tomasin & C. s.n.c. for the video recording; conservator Veronica Collina for helping with the text review.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of this study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

The following abbreviations are used in this manuscript:
OPDOpificio delle Pietre Dure
PNRRPiano Nazionale di Ripresa e Resilienza
VBMVolatile Binding Media
CDDCyclododecane
CDOLCyclododecanone
CDONCyclododecanol
CNFCamphene
MNTL-menthol
MNT_LATL-menthyl lactate

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Figure 1. Giovanni Teutonico, Crucifix, 1494, polychrome wooden sculpture, 174 × 174 cm, chapel of the Crucifix, co-cathedral of Santa Maria Argentea, Norcia (Perugia), before the earthquake. (Credits: Sandro Bellu; © Archidiocesi di Spoleto-Norcia.).
Figure 1. Giovanni Teutonico, Crucifix, 1494, polychrome wooden sculpture, 174 × 174 cm, chapel of the Crucifix, co-cathedral of Santa Maria Argentea, Norcia (Perugia), before the earthquake. (Credits: Sandro Bellu; © Archidiocesi di Spoleto-Norcia.).
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Figure 2. Co-cathedral of Santa Maria Argentea in Norcia during the safety and rescue operations carried out by the firefighters on 12 November 2016, a few days after the earthquake. (Credits: Vigili del Fuoco; https://www.vigilfuoco.tv/umbria/perugia/norcia/recupero-opere-religiose; accessed on 2 October 2025).
Figure 2. Co-cathedral of Santa Maria Argentea in Norcia during the safety and rescue operations carried out by the firefighters on 12 November 2016, a few days after the earthquake. (Credits: Vigili del Fuoco; https://www.vigilfuoco.tv/umbria/perugia/norcia/recupero-opere-religiose; accessed on 2 October 2025).
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Figure 3. Fragments of the Crucifix after the extraction from the ruins: (a) body, limbs, and crown of thorns; (b) part of the face. (Credits: SABAP Umbria; https://www.ansa.it/sisma_ricostruzione/notizie/beni_culturali/2018/02/16/crocifisso-del-1494-tra-macerie-sisma_09f44341-2d00-4fbd-980a-50bac6768c56.html; accessed on 2 October 2025).
Figure 3. Fragments of the Crucifix after the extraction from the ruins: (a) body, limbs, and crown of thorns; (b) part of the face. (Credits: SABAP Umbria; https://www.ansa.it/sisma_ricostruzione/notizie/beni_culturali/2018/02/16/crocifisso-del-1494-tra-macerie-sisma_09f44341-2d00-4fbd-980a-50bac6768c56.html; accessed on 2 October 2025).
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Figure 4. Details of the Crucifix inside the storage building in Santo Chiodo (Spoleto): (a) right side of the abdomen; (b) right shoulder; (c) left leg; (d) right knee.
Figure 4. Details of the Crucifix inside the storage building in Santo Chiodo (Spoleto): (a) right side of the abdomen; (b) right shoulder; (c) left leg; (d) right knee.
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Figure 5. Images at the stereomicroscope of solid-state VBM at room temperature (4× magnification): (a) CDD; (b) CDOL; (c) CDON; (d) CNF; (e) MNT; (f) MNT_LAT.
Figure 5. Images at the stereomicroscope of solid-state VBM at room temperature (4× magnification): (a) CDD; (b) CDOL; (c) CDON; (d) CNF; (e) MNT; (f) MNT_LAT.
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Figure 6. Images at the stereomicroscope of CDD (8× magnification): (a) melted CDD; (b) dripped saturated solution of CDD in cyclohexane; (c) sprayed saturated solution of CDD in cyclohexane.
Figure 6. Images at the stereomicroscope of CDD (8× magnification): (a) melted CDD; (b) dripped saturated solution of CDD in cyclohexane; (c) sprayed saturated solution of CDD in cyclohexane.
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Figure 7. Images at the stereomicroscope of CDOL (8× magnification): (a) melted CDOL; (b) dripped saturated solution of CDOL in acetone; (c) sprayed saturated solution of CDOL in acetone.
Figure 7. Images at the stereomicroscope of CDOL (8× magnification): (a) melted CDOL; (b) dripped saturated solution of CDOL in acetone; (c) sprayed saturated solution of CDOL in acetone.
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Figure 8. Images at the stereomicroscope of CDON (8× magnification): (a) melted CDON; (b) dripped saturated solution of CDON in ethanol; (c) sprayed saturated solution of CDON in ethanol.
Figure 8. Images at the stereomicroscope of CDON (8× magnification): (a) melted CDON; (b) dripped saturated solution of CDON in ethanol; (c) sprayed saturated solution of CDON in ethanol.
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Figure 9. Images at the stereomicroscope of MNT (8× magnification): (a) melted MNT; (b) dripped saturated solution of MNT in acetone; (c) sprayed saturated solution of MNT in acetone.
Figure 9. Images at the stereomicroscope of MNT (8× magnification): (a) melted MNT; (b) dripped saturated solution of MNT in acetone; (c) sprayed saturated solution of MNT in acetone.
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Figure 10. Images at the stereomicroscope of MNT_LAT (8× magnification): (a) melted MNT_LAT; (b) dripped saturated solution of MNT_LAT in acetone; (c) sprayed saturated solution of MNT_LAT in acetone.
Figure 10. Images at the stereomicroscope of MNT_LAT (8× magnification): (a) melted MNT_LAT; (b) dripped saturated solution of MNT_LAT in acetone; (c) sprayed saturated solution of MNT_LAT in acetone.
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Figure 11. Images at the stereomicroscope of melted CNF (4× magnification).
Figure 11. Images at the stereomicroscope of melted CNF (4× magnification).
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Figure 12. Linear graph showing the variation in weight (mg) as a function of time (h) of the melted VBM under controlled conditions (T = 25 ± 1 °C).
Figure 12. Linear graph showing the variation in weight (mg) as a function of time (h) of the melted VBM under controlled conditions (T = 25 ± 1 °C).
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Figure 13. Mock-ups during the test for evaluating the capacity of penetration of VBM. In the enlarged detail within the red box, the dotted line indicates the level of penetration of the volatile binders into the Bologna gesso inside the cylinders.
Figure 13. Mock-ups during the test for evaluating the capacity of penetration of VBM. In the enlarged detail within the red box, the dotted line indicates the level of penetration of the volatile binders into the Bologna gesso inside the cylinders.
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Figure 14. Application of MNT_LAT on the Crucifix: (a) syringe injection of the melted binder; (b) crystalline film on the surface and under the cleavages.
Figure 14. Application of MNT_LAT on the Crucifix: (a) syringe injection of the melted binder; (b) crystalline film on the surface and under the cleavages.
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Figure 15. Details of the Crucifix after the consolidation treatment: (a) torso; (b) right leg and other smaller fragments.
Figure 15. Details of the Crucifix after the consolidation treatment: (a) torso; (b) right leg and other smaller fragments.
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Figure 16. Blocking system designed for transportation of the larger fragments: (a) 3D digital model of the Crucifix with the “masks”; (b) detail of the left heel; (c) some 3D printed “masks”. (Credits: Mattia Mercante).
Figure 16. Blocking system designed for transportation of the larger fragments: (a) 3D digital model of the Crucifix with the “masks”; (b) detail of the left heel; (c) some 3D printed “masks”. (Credits: Mattia Mercante).
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Figure 17. Blocking system realised for transportation of the larger fragments: (a) detail of some masks screwed to the pallet; (b) the pallet with the consolidated and blocked fragments.
Figure 17. Blocking system realised for transportation of the larger fragments: (a) detail of some masks screwed to the pallet; (b) the pallet with the consolidated and blocked fragments.
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Figure 18. The Crucifix placed inside the double crate.
Figure 18. The Crucifix placed inside the double crate.
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Figure 19. The customised walk-in fume hood: (a) digital rendering (credits: Genelab Srl); (b) the Crucifix inside the fume hood after transportation.
Figure 19. The customised walk-in fume hood: (a) digital rendering (credits: Genelab Srl); (b) the Crucifix inside the fume hood after transportation.
Heritage 08 00522 g019
Table 1. Chemical structural formulae of the six tested VBM: cyclododecane (CDD), cyclododecanol (CDOL), cyclododecanone (CDON), camphene (CNF), L-menthol (MNT), and L-menthyl lactate (MNT_LAT).
Table 1. Chemical structural formulae of the six tested VBM: cyclododecane (CDD), cyclododecanol (CDOL), cyclododecanone (CDON), camphene (CNF), L-menthol (MNT), and L-menthyl lactate (MNT_LAT).
CDDCDOLCDONCNFMNTMNT_LAT
Heritage 08 00522 i001Heritage 08 00522 i002Heritage 08 00522 i003Heritage 08 00522 i004Heritage 08 00522 i005Heritage 08 00522 i006
Table 2. Physical and chemical parameters of the tested VBM. The data obtained from the tests for the sublimation rate and the residue rate are also shown.
Table 2. Physical and chemical parameters of the tested VBM. The data obtained from the tests for the sublimation rate and the residue rate are also shown.
CDDCDOLCDONCNFMNTMNT_LAT
Raw formulaC12H24C12H24OC12H22OC10H16C10H20OC13H24O3
CAS number294-62-21724-39-6830-13-779-92-52216-51-559259-38-0
SupplierCTS 1TCI 2TCI 2Sigma-Aldrich 3Sigma-Aldrich 3Sigma-Aldrich 3
Item code01159100-01C0461C0462456055W266590W37480
Lot400FHJ01WWQ3G-IPMKCH6072SHBM6897SHBM7087
Purity (%)100>98>99>94,5>99>97
Density (g/m3)0,82--0,85--
Melting point (°C)60,776–8061–6348–5242–4542–47
Boiling point (°C)247104113159–160212140–142
Flash point (°C)98--2694>113
Auto-ignition point (°C)175380280---
Vapour pressure (hPa)13,3 (at 100 °C)--3,8 (at 20 °C)0,19 (at 25 °C)-
Water solubility (g/L at 20 °C)0,01--0,00420,397-
Cyclohexane solubility
(g/mL at 25 °C)		0,700,570,081,504,400,95
Ethanol solubility (g/mL at 25 °C)-0,480,471,201,000,80
Acetone solubility (g/mL at 25 °C)-0,950,201,503,400,95
Sublimation rate (mg/h at 25 °C) *0,2-0,029,30,20,02
Residue rate (%) *0,7-11,43,50,70,7
LD50/rat (g/kg)>10>2,5>2,5>5>2,9>2,5
1 CTS Conservation, Altavilla Vicentina (VI), Italy. 2 Tokyo Chemical Industry Co., Tokyo, Japan. 3 Merck KGaA, St. Louis, Missouri, USA. * Data obtained from melted VBM.
Table 3. Estimated volume of gesso (cm3) penetrated by 2,0 mL of VBM.
Table 3. Estimated volume of gesso (cm3) penetrated by 2,0 mL of VBM.
MeltedDrop-Applied Solutions
CyclohexaneEthanolAcetone
CDD0,16,1--
CDOL0,015,55,45,9
MNT1,83,74,63,9
MNT_LAT1,73,84,53,7
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MDPI and ACS Style

Amato, V.; Bassi, S.; Pintus, R. Use of the Volatile Binder Menthyl Lactate to Temporarily Consolidate and Transport the Earthquake-Damaged Wooden Crucifix of Santa Maria Argentea in Norcia. Heritage 2025, 8, 522. https://doi.org/10.3390/heritage8120522

AMA Style

Amato V, Bassi S, Pintus R. Use of the Volatile Binder Menthyl Lactate to Temporarily Consolidate and Transport the Earthquake-Damaged Wooden Crucifix of Santa Maria Argentea in Norcia. Heritage. 2025; 8(12):522. https://doi.org/10.3390/heritage8120522

Chicago/Turabian Style

Amato, Vincenzo, Sara Bassi, and Renata Pintus. 2025. "Use of the Volatile Binder Menthyl Lactate to Temporarily Consolidate and Transport the Earthquake-Damaged Wooden Crucifix of Santa Maria Argentea in Norcia" Heritage 8, no. 12: 522. https://doi.org/10.3390/heritage8120522

APA Style

Amato, V., Bassi, S., & Pintus, R. (2025). Use of the Volatile Binder Menthyl Lactate to Temporarily Consolidate and Transport the Earthquake-Damaged Wooden Crucifix of Santa Maria Argentea in Norcia. Heritage, 8(12), 522. https://doi.org/10.3390/heritage8120522

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