HYDROGEL FORMULATION FOR CLEANING STONE SURFACES

Description

TITLE: “Hydrogel formulation for cleaning stone surfaces” DESCRIPTION FIELD OF INVENTION The present invention falls within the technical field of chemical cleaning of surfaces 5 stone, especially of civil / industrial buildings and / or cultural heritage. STATE OF THE ART The stone surfaces (natural or artificial) of civil and industrial buildings are subject to deposition and accumulation of atmospheric particulate matter, carbon residues, products of neoformation or degradation of metal objects with consequent alteration 10 chromatic. The removal of these deposits or patinas is necessary for both reasons aesthetic but, above all, conservative. In addition to the civil sphere, this need is also evident in other contexts, such as that of cultural heritage. Chemical cleaning is the most frequently used technology for the removal of 15 deposit or newly formed material from stone surfaces, as the most sustainable (in terms of material cost and execution time), as well as not requiring highly specialized personnel. Problem of the prior art In particular, chemical cleaning consists of the use of solvents or formulations 20 aqueous for the solubilization and removal of unwanted material from stone surfaces. However, to obtain good results it is often necessary to use organic solvents. or products characterized by varying toxicity. For example, among the most toxic solvents Organic compounds of various nature are commonly used, such as acetone, 25 ethyl or butyl acetate, nitro thinner, ligroin, white spirit, alcohols. Organic solvents are essentially toxic, non-sustainable and / or non-biodegradable, and are used in large quantities. In other cases, the preparation of water-based formulations is instead envisaged. aqueous formulations known in the state of the art are obtained by solubilizing basic or acidic substances - such as sodium or ammonium carbonate / bicarbonate, EDTA, phosphoric acid, ammonia, sodium hydroxide, hydrochloric acid, citrate 5 ammonium or citric acid - with or without surfactants. In the civil sector, the application of organic solvents or aqueous solutions is done generally by spraying, using suitable dispensers, followed by abundant rinsing, often using pressure washers. In other cases, where for technical, ecological and / or physical reasons, it is not possible to proceed 10 with spray application, especially in cleaning historical surfaces- architectural, the cleaning agent (organic solvent or aqueous solution) is generally supported (by applying a “poultice”), at the time of use, on "supporting" agents (also called simply "supporting"), such as, for example example, cellulose pulp, agar-agar, sepiolite, chemical gels (e.g., polymers 15 of acrylic acid), and applied as a compress. This technique of preparing the poultice in situ requires expert personnel - especially in determining the appropriate quantities of the various components and in the their correct mixing - which must then be used within the following 24-48 hours. Furthermore, as for the spray application, once the compress is removed, the surface 20 is then rinsed thoroughly to eliminate unwanted residues of the supporting and cleaning agent. Passaretti et al in “Biologically Derived Gels for the Cleaning of Historical and Artistic Metal Heritage” (Appl. Sci. 2021, 11, 3405. https: / / doi.org / 10.3390 / app11083405) explain that it is possible, for the surfaces 25 metals, use hydrogels or organogels, which are still under development implementation. Again, the authors Guilminot et al in “The Use of Hydrogels in the Treatment of Metal Cultural Heritage Objects.” (Gels. 2023 Mar 2;9(3):191. doi: 10.3390 / gels9030191. PMID: 36975640; PMCID: PMC10048560) explain that, 30 especially for application on metal surfaces, it is possible to use hydrogel based on polysaccharides, such as agar, gellan and xanthan gum. According to the authors, for for cleaning copper alloys, the best results are obtained by combining a gel of agar with a chelating agent (EDTA (ethylenediaminetetraacetic acid) or TAC (tri- ammonium citrate)). Hot application allows you to obtain a “peelable” gel, particularly suitable for historical objects. The authors explain, further, that the 5 successful electrochemical hydrogel treatments for cleaning of silver and for the dechlorination of ferrous or copper alloys. The use of hydrogels for the Cleaning of painted aluminum alloys is possible, but must be combined with the mechanical cleaning. However, for the cleaning of archaeological lead, the use of hydrogels were not found to be very effective. The authors conclude that agar appears 10 to be the most promising hydrogel for this type of application. Similarly, JM van den Burg and K. Seymour in “Dirt and dirt removal (dry and aqueous cleaning)” (2022, Klaas Jan van der Berg and Lia Gorter Editors, Cultural Heritage Agency of the Netherlands, Amersfoort, p. 61) explain that rubber xanthan gum can be used to thicken some aqueous cleaning solutions. It 15 forms a water-based, non-toxic, biodegradable polymer emulsion gel and stable at any pH. Xanthan gum is a polysaccharide polymer consisting of tangled helical chains that, at higher concentrations, aggregate forming small cages that retain water molecules. Oxidizing agents, such as bleach, and most cationic materials, such as ammonia, 20 cannot be used because they cause the gel to collapse. The authors explain that one of the main disadvantages of xanthan gum (and other emulsifiers aqueous) is that, after application, an additional cleaning step is required. Xanthan gum finally requires an aqueous solution to be eliminated. Therefore, from these three scientific articles it is clear that the use of hydrogels for the 25 cleaning of surfaces, especially those belonging to the context of cultural heritage, is known state of the art. In other scientific studies however, such as those conducted by Infurna G, Cavallaro G, Lazzara G, Milioto S, Dintcheva NT. In “Understanding the Effects of Crosslinking and Reinforcement Agents on the Performance and Durability of Biopolymer Films 30 for Cultural Heritage Protection. Molecules” (2021 Jun 7;26(11):3468. doi: 10.3390 / molecules26113468. PMID: 34200367; PMCID: PMC8201363), yes highlights the formation of biofilms (or biopolymeric films) based on chitosan and pectin, also containing natural cross-linking and strengthening agents, such as citric acid (CA) and halloysite nanotubes (HNT). However, these biofilms are not used for cleaning surfaces; rather they are 5 suitable as a covering film for the protection of cultural heritage. Similarly, authors Li T, Hu Y and Zhang B. in “Biomineralization Induced by Colletotrichum acutatum: A Potential Strategy for Cultural Relic Bioprotection” (Front Microbiol. 2018 Aug 14;9:1884. doi: 10.3389 / fmicb.2018.01884. PMID: 30158913; PMCID: PMC6104437) identify an eco-sustainable method for the 10. Conservation of stone artifacts. The authors explain that the Colletotrichum fungus acutatum is capable of initiating biomineralization (phenomenon of formation of the calcium carbonate); in particular, they noted that citric acid is a metabolite produced by C. acutatum. The same authors then evaluated whether the proliferation of C. acutatum could influence the deterioration of stone finds, discovering 15 that, under low carbon conditions, protection of the calcium carbonate from dissolution, thus indicating that the risk of deterioration of calcareous substrates could be controlled if fungi were used to consolidate or restore monuments or stone surfaces. These results suggest that C. acutatum-induced biomineralization may be a 20 useful treatment for deteriorated stone objects. Therefore, in this last case, the authors focus on the capabilities of conservation of stone surfaces, and not on real chemical cleaning techniques and own. Again, the authors Cuvillier, L. et al in “Testing of the siderophore deferoxamine 25 amended in hydrogels for the cleaning of iron corrosion” (Eur. Phys. J. Plus 138, 569 (2023). https: / / doi.org / 10.1140 / epjp / s13360-023-04159-y) disclose the use of siderophores, such as deferoxamine, loaded on polysaccharide hydrogels, for the removal of unwanted corrosion products from iron works of art in a perspective on the biodegradability of the resulting formulation. Siderophores are metabolites 30 secondary proteins capable of binding iron and are produced by microorganisms when these live in areas where the iron concentration is low (to ensure the iron intake necessary for survival). By virtue of their high affinity for iron, siderophores could be used for targeted cleaning of objects compounds from this metal. Three different types of polysaccharides were tested for the formation of hydrogel, among which are agar, gellan gum and gum 5 xanthan, obtaining better results for the first two polysaccharides. The disclosure “Sitting pretty: collaborative treatment of an early Yayoi Kusama soft-sculpture chair” Baas F. and Hartman LE; Proceedings of the Objects Specialty Group Sessions; May 28‒June 2, 2017; 45th Annual Meeting Chicago, Illinois. https: / / faic.wpenginepowered.com / osg-postprints / wp- 10 content / uploads / sites / 8 / 2019 / 12 / osg024-017.pdf provides for the use of two different types of gels, including xanthan gum, Pemulen TR2 (a polymer derived from acrylic) and agarose. Xanthan gum and Pemulen TR2 provide a solution liquid gel with a consistency similar to honey or hair gel, while Agarose produces a rigid, rubbery gel. The authors focused on testing 15 with liquid gels. The citric acid solution was gelled with gum xanthan and Pemulen TR2. The authors explain that, since xanthan gum remains structurally more stable as a gel over a wider range of pH parameters and conductivity, was chosen over the use of Pemulen TR2. As can be seen from the state of the art, mixtures of citric acid, xanthan gum and 20 mixtures of citric acid and other chelating agents, although known, are prepared shortly before use (on-site preparation) according to variable and personalized recipes, characterized by a stability limited to 24-48 hours and an aggressiveness not certified or certainly not negligible, without providing for a controlled and progressive release of the cleaning solution, thus affecting the benefits of the cleaning effectiveness. 25 Therefore, the Applicant believes that several further inconveniences must be addressed. resolved, including: - the need to identify water-based formulations that involve the use of cleaning agents effective on various lithotypes and on various types of dirt / deposits / patinas, that they are non-toxic for operators and eco-sustainable, i.e. without any impact 30 on the environment; - the need to identify supporting agents capable of ensuring cleaning effective and a controlled (slow) release of the cleaning agent, so as to have a surface wettability and, consequently, easy cleaning control, in this way reducing, as much as possible, the chemical aggression of the matrix or 5 of the innermost part of the material of the surface to be treated, in addition to avoiding the penetration of dirt and / or other unwanted material into the depth of the material of the surface to be treated; - the need, again, to identify a standardized or ready-to-use formulation, that it is easy to apply on surfaces of any geometry, placed both in 10 horizontal and vertical, as well as easy to produce on an industrial level; - the need to easily remove the formulation / pack, applying a mild rinsing the surface, avoiding wasting large quantities of water; - finally, it is also required to obtain a product that is stable over time, which retains its properties and cleaning effectiveness performance over a relatively long period of time 15 long, for example for more than a week and up to about a year, under conditions of standard preservation. The known formulations, in addition to not being ready for use, are in fact characterised by a minimum conservation of 24 hours up to a maximum of 48 hours. SUMMARY OF THE INVENTION 20 A first object of the invention is a surface cleaning hydrogel formulation stone including - a first chelating agent consisting of citric acid, - a second chelating agent chosen from the group consisting of: Tetrasodium glutamate diacetate, Trisodium dicarboxymethyl alaninate and combinations of the above, 25 - a supporting agent consisting of xanthan gum, - at least one co-thickener, - at least one surfactant, - at least one antibacterial and / or anti-mold, - waterfall, where the weight ratio between the sum of the first chelating agent and the second chelating agent and xanthan gum is between 1:0.7 and 1:1.6. A second object of the invention is a method of application on a surface stone of the above formulation, including the phases of 5 a) apply the hydrogel formulation on the stone surface, b) leave to act for between 15 minutes and 120 minutes, c) remove the hydrogel formulation with water, where the aforementioned phases a)-c) are repeated for a number of times n between 1 and 3. A third further object of the invention is the use of the above formulation for the 10 cleaning, preferably chemical cleaning, of stone surfaces. Advantages of the invention Note that the interaction “first chelating agent / second chelating agent” is of particular importance. chelating agent / supporting agent” because, in addition to the complexing role of the former two, it is also possible to ensure that a precise conformation is achieved 15 three-dimensional hydrogel through the formation of van der Waals forces. This ensures a controlled release of the formulation, good cleaning performance and a minor or negligible aggressiveness of the stone surface. In particular, the technical advantages of the invention are summarized below: - identification of a water-based formulation with cleaning efficacy, which 20 includes effective cleaning agents that are non-toxic for the environment or for operators, and also eco-sustainable; - identification of supporting agents capable of ensuring effective cleaning and controlled / slow release of the cleaning agent, a mainly wettability superficial and, consequently, a lower or negligible chemical aggressiveness 25 of the surface of the material to be treated, with easier control of cleaning, even compared to the cleaning solutions or cleansing compresses known to date; - the creation of a poultice without releasing residues on the stone surface deal with; - identification of a ready-to-use formulation, in the sense that it does not require need to mix the necessary ingredients on site, and is easy to apply on horizontal, vertical and moulded surfaces; - the ability to easily remove the formulation / pack, applying a 5 gentle rinsing of the surface, avoiding wasting water; - the ability to achieve a formulation that is stable over time, in the sense that retains its properties and cleaning effectiveness for more than a week and at least one year, under standard storage conditions. Always in terms of storage, no particular critical issues (flammability) or precautions to be taken have emerged 10 follow (corrosion of storage vessels); - the ability to obtain the formulation even at an industrial level, without the need to follow specific technical precautions. Finally, it should be noted that the application times of the formulation of the invention are typically longer than those for freshly prepared formulations 15 (usually under 15 minutes). This allows for greater control of the cleaning power, reducing surface aggression when found unable to meet the exposure times. DESCRIPTION OF THE FIGURES Figure 1: Image of a Carrara marble slab before cleaning. 20 to Example 2. Figure 2: Image of the overall situation after various cleaning tests of which to Example 2. Figure 3: Image of test # H5v1 after one hour and two hours of application, of which to Example 2. 25 Figure 4: Image of test # H9 after one hour and two hours of application, of which to Example 2. Figure 5: Image of test #H10 after one hour and two hours of application, of which to Example 2. Figure 6: Image of test # H12 after one hour, two and three hours of application, of which to Example 2. Figure 7: Image of test # H5v4 after one hour and two hours of application, of which to Example 2. 5 Figure 8: Image of test # L6c after one hour and two hours of application, of which to Example 2. Figure 9: Image of test # L6Neutral after one hour and two hours of application, of referred to in Example 2. Figure 10: Image of test # L9v3 after one hour and two hours of application, of which 10 to Example 2. Figure 11: Image of test # L9v4 after one hour, two hours and three hours of application, of referred to in Example 2. Figure 12-14: Test image # H5v1 before application respectively, after one hour of application and after two hours of application as in Example 3. 15 Figures 15-17: Test image # H9 before application, after application respectively one hour of application and after two hours of application as in Example 3. Figure 18-20: Test image # H10 before application respectively, after one hour of application and after two hours of application as in Example 3. Figures 21-23: Test image # H12 before application respectively, 20 after one hour of application and after two hours of application as in Example 3. Figure 24-26: Test image # H5v4 before application respectively, after one hour of application and after two hours of application as in Example 3. Figures 27-29: Test image # L6c before application, after application respectively one hour of application and after two hours of application as in Example 3. 25 Figures 30-32: Test image # L6Neutral respectively before of the application, after one hour of application and after two hours of application of which to Example 3. Figure 33-35: Test image # L9v3 before application respectively, after one hour of application and after two hours of application as in Example 3. Figure 36-38: Test image # L9v4 before application respectively, after one hour of application and after two hours of application as in Example 3. 5 Figure 39: Clockwise: top left rectangle with straight full line outline (formulation of the invention: Citric acid 3%; Na -GLDA 3%; Xanthan 5%; DPM 3%; 2Prop 3%; Tridac 1%; Water 82%); top right rectangle with outline dotted (composition: Citric acid 2%; Xanthan gum 3%; Water 95%); rectangle central right with dashed outline (composition: Citric acid 2%; Xanthan gum 10 3%; 2Prop 3%; Water 92%); bottom right rectangle with dot-dash outline (composition: Citric acid 3%; Na -GLDA 3%; Xanthan 3%; DPM 3%; 2Prop 3%; Tridac 1%; Water 84%); bottom left rectangle with solid line outline not straight (composition: Citric acid 2%; Xanthan 3%; 2Prop 3%; Tridac 1%; Water 91%). 15 Figures 40-43: Optical microscope images, Line H, in order: NT (Non Treated), 40 mesh, 80 mesh, 200 mesh. Treatment: 1h+1h. Figures 44-45: Optical microscope images, Line H, in NT order (Non Treated), 40 mesh. Treatment: 24 h. Figures 46-49: Optical microscope images, Line L, in order: NT (Non 20 Treated), 40 mesh, 80 mesh, 200 mesh. Treatment: 1h+1h. Figures 50-51: Respectively: pre-treatment situation image and image of the situation after 3 types of treatments (at 2h, at 1h and at 1h+1h) for three Test# of the H line (respectively at 40, 80 and 200 mesh). DETAILED DESCRIPTION OF THE INVENTION 25 In the following, the invention and its embodiments are described in more detail. favorite realizations. Please note that although the structure has been organized into paragraphs and subparagraphs, the information contained in each section or paragraph or subsection or subparagraph are not isolated and can be combined with those contained in other sections / paragraphs or, more generally, with other information contained in the text of the patent application. Hydrogel formulation for cleaning stone surfaces By hydrogel (or hydrogel) we mean a colloid in which the polymer chains of the 5 molecules of the supporting agent xanthan gum are dispersed in water, where the water is in an amount ≥ 80% by weight, preferably ≥ 80% and ≤ 95% by weight, on the total weight of the formulation. In this sense, the formulation is in gel form to be applied to a stone surface as a poultice. By cleaning formulation of stone surfaces it is meant that the formulation 10 of the invention is suitable for removing deposit or newly formed material from the stone surfaces. Stone surfaces can be natural, artificial or made from ancient plaster. Examples of stone surfaces are chosen from the group consisting of: marble, sandstone, travertine, granite, limestone, terracotta, concrete conglomerates. 15 Again, this formulation may be preferably useful for treating stone surfaces selected from: carbonate stones; for example Carrara marble; stones limestone, such as Lecce stone; silicate stones, such as Pietra Serena; artificial stones, such as bricks; building surfaces, such as stones or bricks, which, once installed, are not plastered (“exposed face”). 20 Preferably, the deposit or unwanted material to be removed, preferably placed at surface level, it can be: atmospheric particulate matter, carbon residues, products of neoformation or percolations from degradation of metal objects (iron and copper, both superficial and slightly internal to the matrix), black crusts, and their combinations. 25 In the context of the invention, a cleaning agent or solution (or mixture) means a chemical compound or a solution / mixture of chemical compounds capable of promoting cleaning of stone surfaces, removing deposits or unwanted material, which it acts at a mainly superficial level. Preferably, the hydrogel formulation is an environmentally friendly and / or eco-friendly product, 30 in the sense that it contains ecological and / or eco-friendly ingredients in a quantity between 80% and 100% by weight, preferably between 90% and 100% by weight, on the weight total formulation. This is advantageous in terms of environmental sustainability. An ecological and / or eco-compatible product or formulation means a compound chemical or a mixture of chemical compounds designed and manufactured in such a way as to 5 minimize environmental impact, ensure low risk to human health and ensure easy disposal (Legislative Decree 152 / 2006). For product / formulation ecological and / or eco-compatible means a formulation characterised by having: - components of natural origin or biodegradable, and - high reduction of polluting emissions during the life cycle, and 10 - absence or minimal quantity of toxic, persistent and bioaccumulative substances. First chelating agent Citric acid is the primary chelating agent. It is a cleansing agent. Citric acid is preferably in an amount between 0.9% and 4% by weight, preferably between 1% and 4% by weight, preferably between 1.2% and 4% by weight, 15 preferably between 1.2% and 3% by weight, preferably between 1.35% and 3% by weight, preferably equal to 1.2%, or 1.35% and 3% by weight, on total weight of the formulation. Second chelating agent The second chelating agent is chosen from the group consisting of: Tetrasodium glutamate 20 diacetate, Trisodium dicarboxymethyl alaninate and combinations of the above. second chelating agent is a cleansing agent. Preferably, the second chelating agent is Tetrasodium glutamate diacetate or Trisodium dicarboxymethyl alanine or a combination of the above. Preferably, the second chelating agent is in an amount between 2% and 25 6.7% by weight, preferably between 3% and 5.5% by weight, preferably between 3% and 5.2% by weight, preferably equal to 3% or 4.65% or 5.1% by weight, on the weight total of the formulation. Preferably, when the second chelating agent is Tetrasodium glutamate diacetate, the relative quantity is between 2% and 3.5% by weight, preferably between 3% and 3.5% by weight, preferably equal to 3% or 3.5% by weight, of the total weight of the formulation. Preferably, when the second chelating agent is Trisodium dicarboxymethyl alaninate, the relative quantity is between 1% and 4.7% by weight, preferably 5 between 1.5% and 4.65% by weight, preferably equal to 1.6% or 4.65% by weight, on the weight total of the formulation. Preferably, when the second chelating agent is the combination of Tetrasodium glutamate diacetate and trisodium dicarboxymethyl alanine, the relative quantity is between 2% and 6.7% by weight, preferably between 3% and 5.5% by weight, 10 preferably equal to 5.1% by weight, on the total weight of the formulation. The Applicant wishes to underline that the quantity of the second chelating agent influences the pH of the formulation, as well as the surface aggression effect. increase of the second chelating agent, for example beyond the maximum limit expressed at the above intervals, has a negative impact on these two parameters (see 15 Examples 1-5). Supporting Agent By supporting agent we mean a material suitable for generating a hydrogel in presence of water, capable of forming the poultice to be applied on a surface stone; it promotes the progressive release of the cleaning solution. In this 20 sense, the supporting agent acts as a thickening agent. A thickener is a chemical compound capable of modifying the consistency or the viscosity over time of the formulation. The supporting agent is xanthan gum. Preferably, xanthan gum is in an amount between 4.7% and 8% in 25 weight, preferably between 5% and 8% by weight, preferably between 5% and 6% by weight, preferably equal to 5% or 6% by weight, on the total weight of the formulation. Preferably, the grain size of xanthan gum is between 30 and 50 mesh, preferably 40 mesh. The Applicant noted that the use of this particle size range for the xanthan gum shows different and better performances than the others two commercially available versions, 80 and 200 mesh, especially in terms of rheological, physical, controlled release properties, therefore control of the 5 surface wettability, properties which influence the cleaning power and the stability of the formulation. As can be seen from Example 5, the tests carried out with xanthan gum at 80 and 200 mesh showed, after 20 days of realization, the formation of crystalline concretions in the gelatinous matrix consisting of secondary recrystallizations of the chelating agents, formed during the 10 phase of complete hydration of the gelling agent, which however altered the compound reducing its stability and performance. By weight ratio between the sum of the first chelating agent and the second chelating agent and xanthan gum means the ratio defined by the formula (I) following 15 (I) (𝑎𝑢𝑡𝑛𝑖𝑞𝑡𝑣𝑎𝑜𝑡𝑖 𝑜𝑝𝑟𝑖𝑚 𝑎𝑡𝑛𝑔𝑒𝑒 ℎ 𝑐 𝑙𝑒𝑎𝑡𝑛𝑒 + 𝑎𝑢𝑡𝑛𝑖𝑞𝑡𝑣𝑎𝑜𝑡𝑖 𝑠𝑐𝑒 𝑜𝑜𝑛𝑑 𝑎𝑡𝑛𝑔𝑒𝑒 ℎ 𝑐 𝑒𝑙𝑒𝑎𝑡𝑛 ) ∶ 𝑎𝑢𝑡𝑛𝑖𝑞𝑡𝑣𝑎𝑜𝑡𝑖 𝑔𝑜𝑚𝑚𝑎 𝑥𝑎𝑡𝑛𝑎𝑎𝑛 . The sum of the first chelating agent and the second chelating agent means sum of the quantity of the first chelating agent and the quantity of the second chelating agent. 20 Please note that this weight ratio ensures cleaning effectiveness, gradual release and controlled cleaning agents at the stone surface level, i.e. without penetrate into the matrix of the stone material. The weight ratio between the sum of the first chelating agent and the second chelating agent and xanthan gum is between 1:0.6 and 1:1.6, preferably 25 between 1:0.7 and 1:1.4. Preferably, the weight ratio between the sum of the first chelating agent and of the second chelating agent and xanthan gum is preferably included between 1:0.7 and 1:1.4, preferably between 1:0.7 and 1:1.35, preferably between 1:0.79 and 1:1.35, preferably between 1:0.79 and 1:1.34, preferably between 1:0.79 and 1:1.34 or 30 between 1:0.79 and 1:1. According to a preferred form, the weight ratio between the sum of the first chelating agent and the second chelating agent and xanthan gum is 1:0.79, or it's 1:0.83 or it's 1:1. Co-thickener 5 A co-thickener is a chemical compound that assists the action of a main thickening agent, which in this case is xanthan gum. Preferably, the at least one co-thickener is selected from the group consisting of: Dipropylene glycol monomethyl ether, dipropopylene glycol dimethyl ether, propylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl 10 ether, dipropylene glycol, and combinations of the above. Preferably, the at least one co-thickener is dipropylene glycol monomethyl ether (“DPM”). Preferably, the at least one co-thickener is in an amount between 2% and 4% by weight, preferably equal to 3% by weight, of the total weight of the formulation. 15 Surfactant A surfactant is a chemical substance that can lower the pressure surface of a liquid, facilitating the wettability of the surfaces. Preferably, the surfactant used for the purposes of the invention is a surfactant not soluble in water at room temperature. 20 Preferably, the at least one surfactant is selected from the group consisting of: a polyethylene glycol ether of a fatty alcohol, an alkyl polyethylene glycol of a fatty alcohol, an ethoxylated propoxylated fatty alcohol, a polypropylene glycol / polyethylene glycol ether of a hydrogenated fatty alcohol, a polyoxyalkylated fatty alcohol ether, and combinations of the above. 25 Preferably, the at least one surfactant is polyethylene glycol ether of a fatty alcohol, preferably the commercial product Tridac Iso-3. Preferably, the at least one surfactant is in an amount between 0.5% and 2% by weight, preferably equal to 1% by weight, of the total weight of the formulation. Preferably, the weight ratio between the sum of the at least one co- thickener and surfactant and xanthan gum is between 1:1.2 and 1:2. The sum of at least one co-thickener and the surfactant means sum of the quantity of at least one co-thickener and the quantity 5 of at least one surfactant. Preferably, the weight ratio between the sum of the at least one co- thickener and surfactant and xanthan gum is between 1:1.2 and 1:1.5, preferably between 1:1.25 and 1:1.5. According to a preferred form, the weight ratio between the sum of the at least one 10 co-thickener and surfactant and xanthan gum is between 1:1.25 and 1:2, or equal to 1:1.25. According to a further preferred form, the weight ratio between the sum of at least one co-thickener and surfactant and xanthan gum is included between 1:1.25 and 1:1.5, or equal to 1:1.5. 15 Note that this weight ratio is useful to assist the cleaning effectiveness, the controlled release of cleaning agents at the stone surface level, i.e. without penetrate into the matrix of the stone material, and the stability of the formulation. This ratio allows optimal adhesion of the hydrogel pack to the surfaces of interest, without compromising its subsequent easy removal, ensuring the 20 at the same time precise control over the diffusion of the solvent, limiting it to the area hydrogel / surface contact. Antibacterial and / or anti-mold The antibacterial and / or anti-mold agent is a chemical substance capable of counteracting the bacterial growth and / or mold within the formulation. 25 Preferably, at least one antibacterial and / or anti-mold is chosen from the group consisting of from: isopropanol, ethanol, phenylethyl alcohol, benzyl alcohol, pentylene glycol, isobutyl alcohol, and combinations of the above, preferably isopropanol. Preferably, the at least one antibacterial and / or anti-mold is in a quantity between 2% and 4% by weight, preferably 2.999% by weight, of the total weight 30 of the formulation. The Applicant noted that the analyses conducted on the role of isopropanol in formulation have allowed us to recognize that, in addition to its active effect deriving due to its nature as an alcoholic solvent, it plays a significant preventive role in the formation of mold and biological alterations during the storage phase. 5 This feature makes the formulation not only suitable for production, but also to effective conservation over time, satisfying the stability over time of the formulation (see Example 5.5). Waterfall Water is preferably in an amount ≥ 80% by weight, preferably between 80% 10 to 90% by weight, preferably between 80% and 85% by weight, preferably approximately 81%, or 81.701% by weight, or 82% by weight, of the total weight of the formulation. Note that the first chelating agent is citric acid, the second agent chelating agent, at least one co-thickener, at least one surfactant, at least one 15 antibacterial and / or anti-mold and water constitute the cleaning solution or mixture that is loaded and dispersed in the supporting agent xanthan gum to obtain the hydrogel compress formulation. Preferably, the formulation of the invention is characterized by a pH that varies between 4 and 7.6, preferably between 4.1 and 6.6, or, alternatively, 20 preferably between 6.6 and 7.2, preferably equal to 4.5 or 6.6 or to 7.2. From the pH ranges just indicated, the range is preferably excluded between 5 and 5.5. The Applicant believes that the pH of the formulation, which derives from the purpose qualitative-quantitative balance of the formulation components described in 25 previous sections, influence the cleaning effectiveness, but also the surface aggressiveness (see Examples 1-3). First embodiment: cleaning hydrogel formulation for stone surfaces civil buildings or civil assets Civil buildings or civil assets are understood to mean assets of civil and public interest, such as 30 of which are intended for homes, shops, etc. According to a first embodiment, the cleansing hydrogel formulation of stone surfaces of civil goods includes - a first chelating agent consisting of citric acid, - a second chelating agent consisting of Tetrasodium glutamate diacetate, 5 - a supporting agent consisting of xanthan gum, - at least one co-thickener, - at least one surfactant, - at least one antibacterial and / or anti-mold, - waterfall. 10 The technical specifications of the above components are the same as those reported in the previous sections. Preferably, the weight ratio between the sum of the first chelating agent and of the second chelating agent and xanthan gum is preferably included between 1:0.8 and 1:1.34, preferably equal to 1:0.83. 15 Preferably, the weight ratio between the sum of the at least one co- thickener and surfactant and xanthan gum is between 1:1.25 and 1:2, preferably 1:1.25. Preferably, the formulation of the invention is characterized by a pH that varies between 4.1 and 4.5, preferably 4.5. 20 According to a further preferred alternative in accordance with this first form realization, the hydrogel formulation for cleaning stone surfaces of civil goods comprehends - a first chelating agent consisting of citric acid, - a second chelating agent consisting of: Tetrasodium glutamate diacetate and 25 Trisodium dicarboxymethyl alanine, - a supporting agent consisting of xanthan gum, - at least one co-thickener, - at least one surfactant, - at least one antibacterial and / or anti-mold, - waterfall. The technical specifications of the above components are the same as those reported 5 in the previous sections. Preferably, the weight ratio between the sum of the first chelating agent and of the second chelating agent and xanthan gum is preferably included between 1:0.79 and 1:1.34, preferably between 1:0.79 and 1:1.3, preferably equal to 1:0.79. Preferably, the weight ratio between the sum of the at least one co- 10 thickener and surfactant and xanthan gum is between 1:1.25 and 1:2, preferably 1:1.25. Preferably, the formulation of the invention is characterized by a pH that varies between 6.8 and 7.5, preferably between 6.8 and 7.2, preferably equal to 7.2. Second embodiment: cleaning hydrogel formulation for stone surfaces 15 of cultural heritage Cultural heritage refers to assets that have artistic, historical, archaeological. According to a first embodiment, the cleansing hydrogel formulation of stone surfaces of cultural heritage includes 20 - a first chelating agent consisting of citric acid, - a second chelating agent consisting of Trisodium dicarboxymethyl alanine, - a supporting agent consisting of xanthan gum, - at least one co-thickener, - at least one surfactant, 25 - at least one antibacterial and / or anti-mold, - waterfall. The technical specifications of the above components are the same as those indicated in the previous sections. Preferably, the weight ratio between the sum of the first chelating agent and of the second chelating agent and xanthan gum is preferably included between 5 1:0.8 and 1:1, preferably equal to 1:1. Preferably, the weight ratio between the sum of the at least one co- thickener and surfactant and xanthan gum is between 1:1.25 and 1:1.5, preferably equal to 1:1.5. Preferably, the formulation of the invention is characterized by a pH that varies 10 between 6.4 and 7, preferably between 6 and 6.6, preferably equal to 6.6. Use of the hydrogel formulation for cleaning stone surfaces A further object of the invention is the use of the formulation according to the invention. for cleaning, preferably chemical cleaning, of stone surfaces. The formulation is the one described in the previous sections, preferably also in 15 agreement with the first and second embodiment. Preferably, the use of the formulation is for cleaning stone surfaces of civil buildings, preferably in accordance with the first embodiment above described, - wherein the second chelating agent is Tetrasodium glutamate diacetate, or, in 20 alternative, the second chelating agent is the combination of Tetrasodium glutamate diacetate and Trisodium dicarboxymethyl alaninate, - where the weight ratio between the sum of the first chelating agent and the second chelating agent and xanthan gum is preferably included between 1:0.79 and 1:1.35, preferably between 1:0.8 and 1:1.35, preferably between 1:0.8 and 1:1.3, 25 preferably equal to 1:0.79 or 1:0.83, - where the pH of the formulation is between 4.1 and 4.5, preferably equal to 4.5, or, alternatively, the pH is preferably between 6.8 and 7.5, preferably between 6.8 and 7.2, preferably equal to 7.2. Alternatively, the formulation is used for cleaning stone surfaces of cultural assets, preferably in accordance with the second embodiment above described, - where the second chelating agent is Trisodium dicarboxymethyl alanine, 5 - where the weight ratio between the sum of the first chelating agent and the second chelating agent and xanthan gum is preferably between 1:0.8 and 1:1, preferably between 1:0.83 and 1:1, preferably equal to 1:1, - where the pH of the formulation is between 6.4 and 7, preferably between 6 and 6.6, preferably it is 6.6. 10 Method of application of the hydrogel formulation on a stone surface cleaning A third object of the invention is the method of application on a surface stone of the formulation according to the invention, comprising the steps of a) apply the hydrogel formulation on the stone surface, 15 b) leave to act for a period of between 15 and 120 minutes, preferably between 30 and 90 minutes, preferably between 45 and 90 minutes, preferably equal to 60 minutes, c) remove the hydrogel formulation with water, preferably using a swab soaked in water, preferably the water is demineralized, where the above mentioned phases a)-c) (i.e. respectively the phases of: applying the formulation 20 hydrogel on the stone surface; leave to act; remove the hydrogel formulation with water) are repeated for a number of times n between 1 and 3, preferably between 1 and 2, preferably n is 1 or 2. Preferably for use in cleaning stone surfaces of buildings or civil goods, the formulation can be applied on the surface, then left to act for a 25 time between 45 and 90 minutes, preferably between 45 and 60 minutes, after which rinse with water, reapply the formulation for a time between between 45 and 90 minutes, preferably between 45 and 60 minutes, and rinse again. Preferably for use in cleaning stone surfaces of cultural heritage, the formulation can be applied on the surface, then left to act for a time between 45 minutes and 60 minutes, after which it is rinsed with water. In in this case, is a second application of the formulation possible or not in the same period of time just mentioned followed by rinsing. Preferably, the formulation is applied to the stone surface by hand or 5 by any suitable means known to a technician in the sector, such as a spatula or brush. Please note that, although the action times of the formulation are longer than those of the known formulations, the overall time required for cleaning can be lower as it can be optimised during the application phase. 10 Preferably, under standard conditions (at room temperature), the formulation hydrogel has a shelf life > 7 days, preferably > 7 days and ≤ 1 year and medium, preferably > 7 days and ≤ 1 year. Preferably, the hydrogel formulation is not applied by spray techniques. Preferably, the hydrogel formulation does not contain organic solvents of a natural nature 15 toxic and / or unsustainable. Preferably, the hydrogel formulation does not contain traditional and / or toxic chelators and / or non-environmentally sustainable, such as EDTA, NTA or organophosphonates. EXAMPLES Below are some examples for illustrative and non-limiting purposes. 20 Glossary NT = Untreated; Na -GLDA = Tetrasodium glutamate diacetate; Na -MGDA = Trisodium dicarboxymethyl alanine; 2 Prop = isopropanol; 25 DPM = Dipropylene glycol monomethyl ether; Tridac (or Tridac Iso-3) = polyethylene glycol ether of a fatty alcohol. Example 1: pH of the formulation based on its qualitative chemical composition quantitative 2 Prop + Acid Na4- Na3- Rubber Test # DPM + HO pH Citric GLDA MGDA Xanthan Gum Tridac H5v1 3% 3% - 7% 5% 82% 4.5 H5v4 2.8% 3.2% - 7% 5% 82% 5.5 H9 4% 2% - 7% 5% 82% 3.4 H10 1% 5% - 7% 5% 82% 7.6 H12 3% 3% - 7% 8% 79% 4.1 L6C 0.94% 4.72% 1.89% 6.60% 4.72% 81.13% 8.9 L6Neutral 1.2% 3.5% 1.6% 7% 5% 81.7% 7.2 L9v3 1.35% - 4.65% 7% 5% 82% 6.6 L9v4 1.35% - 4.65% 7% 6% 81% 6.6 Table 1 Note that the Test# formulations reported in Table 1 are also used in the 5 next examples (Examples 2, 3 and 4). Example 2: Evaluation of the cleaning effectiveness of the formulation of the invention Figures 1-11 show photos of a sample of Carrara marble. characterized by superficial encrustations of iron oxide, before and after the various applications of the different formulations Test# of Table 1. 10 The cleaning efficiency results are shown in the following Table 2. Test# Macroscopic morphological description Figure of Hours of application reference Excellent cleaning with just one application 1h (preferably for applications in civil sphere) H5v1 Figure 3 Excellent cleaning, aggression is noticeable 1h+1h surface (preferably for civil applications) Excellent cleaning, surface aggression 1h even after just 1 application H9 Figure 4 Excessive cleaning, aggression 1h+1h marked superficial Light and controlled cleaning, suitable for 1h cultural heritage H10 Figure 5 Excellent cleaning, but signs of wear are visible 1h+1h superficial aggression Excellent cleaning with just one application 1h (preferably for applications in civil sphere) Excellent cleaning, aggression is noticeable H12 Figure 6 1h+1h surface (preferably for civil applications) Excessive cleaning, aggression 1h+1h+1h marked superficial Excellent cleaning, surface aggression H5v4 Figure 7 1h even after just 1 application Excessive cleaning, aggression 1h+1h marked superficial 1h Light cleaning, suitable for cultural heritage L6C Figure 8 Light cleaning with aggression 1h+1h superficial Good cleaning with light aggression 1h superficial L6Neutral Figure 9 Excellent cleaning with aggression 1h+1h superficial Good cleaning, superficial aggression 1h negligible (preferably suitable for the cultural heritage) L9v3 Figure 10 Excellent cleaning, surface aggression 1h+1h light (preferably suitable for goods cultural) Good cleaning, superficial aggression 1h negligible (preferably suitable for the cultural heritage) Excellent cleaning, surface aggression L9v4 Figure 11 1h+1h negligible (preferably suitable for the cultural heritage) Excellent cleaning, surface aggression 1h+1h+1h very light (preferably suitable for the cultural heritage) Table 2 Distinguishing the cleaning effect from the surface aggression effect, it can be noted that for all tests# a good / excellent degree of cleanliness is obtained. Example 3: Evaluation of the aggression of carbonate surfaces by formulation of the invention 5 Morphological results were acquired by optical microscope, relative to the aggression of surfaces by the Test# formulations reported in Example 1. The images were acquired on undegraded Carrara marble specimens before of the treatment, after 1 hour of application and after 1 hour + 1 hour of application. Rinse It was done using a cotton swab soaked in demineralized water. 10 The results of an overall evaluation are reported in Table 3 below. Test# Reference figure Result H5v1 Figures 12-14 Aggressive H9 Figures 15-17 Very aggressive H10 Figures 18-20 Very aggressive H12 Figures 21-23 Aggressive H5v4 Figures 24-26 Very Aggressive L6C Figures 27-29 Aggressive L6Neutral Figures 30-32 Aggressive L9v3 Figures 33-35 Slightly Aggressive L9v4 Figures 36-38 Very little aggressive Table 3 According to the Applicant, tests with an “Aggressive” outcome can be in any case preferably used for civil applications, for buildings or civil goods, as they are characterized by a good level of cleanliness. This is because, although the tests# 15 (for example, tests # H5v1 and H12) are overall “Aggressive”, such evaluation is carried out considering both the outcome after 1 hour of application and the one after 1h+1h of application. Example 4: Evaluation of the release capacity of the cleaning solution of various compositions. 5 With reference to Figure 39, note that the formulation of the invention (top left rectangle with straight solid line outline; Citric acid 3%; Na -GLDA 3%; Xanthan Gum 5%; DPM 3%; 2Prop 3%; Tridac 1%; Water 82%) not shows contour halos, indicating a controlled release capacity of the solution cleansing from the hydrogel pack. 10 As highlighted by the arrows instead, for the other compositions, different from the formulation of the invention (each in the absence of at least one component considered essential for the realization of the formulation of the invention), they notice halos surrounding the hydrogel pack, a sign of an ability to immediate (therefore uncontrolled) release of the cleaning solution. 15 Below is Table 4 summarizing the conclusions from Examples 1-3. Na-Na-Gum Acid 4 3 Test # pH Citric GLDA MGDA Xanthan Gum Notes (%) (%) (%) (%) Aggressive, easy to apply and removal, excellent cleaning H5v1 4.5 3 3 - 5 with light aggression to long application times. Very aggressive, easy applicability and removal, H9 3.4 4 2 - 5 excessive cleaning even at short application times. Very aggressive, easy H10 7.6 1 5 - 5 applicability and removal, excessive cleaning especially at long application times. Aggressive, applicability and critical removal, excellent H12 4.1 3 3 - 8 cleaning, but marked long-term aggression application. Very aggressive, easy applicability and removal, H5v4 5.5 2.8 3.2 - 5 excessive cleaning even at short application times. Aggressive, easy to apply and removal, poor cleaning L6C 8.9 0.94 4.72 1.89 4.72 with long-term aggression of application. Aggressive, easy to apply and removal, good cleaning to short times with light L6Neutral 7.2 1.2 3.5 1.6 5 aggression, excellent cleaning long times with aggression superficial. Slightly aggressive, easy applicability and removal, good cleaning in a short time, L9v3 6.6 1.35 - 4.65 5 excellent long-term cleaning with light aggression to long application times. Very little aggressive, easy applicability and removal, L9v4 6.6 1.35 - 4.65 6 good cleaning in a short time, excellent long-term cleaning with negligible aggression to long application times. Table 4 Example 5: Performance evaluation of xanthan gum at various granulometries. Following the information regarding the market prices of rubber 5 of Xanthan Gum, we report the main strengths and weaknesses of the 3 types available on the market, namely Xanthan gum with grain size 40, 80 or 200 mesh. The formulations prepared with the 3 different granulometries are reported, both for the Line H and Line L. Acid Gum Test # GLDA MGDA 2 Prop DPM Mesh HO Citric Xanthan H5v1 3% 3% - 3% 3% 5% 40 82% L5v1 1% 5% 2% 3% 3% 5% 40 80% H5v3 3% 3% - 3% 3% 5% 80 82% L5v3 1% 5% 2% 3% 3% 5% 80 80% H4 3% 3% - 3% 3% 5% 200 82% L4 1% 5% 2% 3% 3% 5% 200 80% 10 Table 5 5.1 Superficial aggression The aggressiveness of the compositions in Test# was tested on marble samples of healthy Carrara, that is, without alterations, deposits or surface encrustations. The obtained effects were investigated by observing the stone surfaces at 15 SEM and OPTICAL MICROSCOPE in grazing light. The results can be summarized as follows: - SEM: 40 mesh formulations are less aggressive on the surface of the support, when compared with those at 80 and 200, although this analysis did not give the expected results, the images were disturbed due to the difficulty of processing and image acquisition; 5 - OPTICAL MICROSCOPE: refer to Figures 40-49, which show the images acquired for visual comparison. Here too, as with the SEM, it was observed greater aggressiveness in products with 80 and 200 mesh Xanthan gum compared to to the one made with 40 mesh powder. The presence of deposits is reported superficial, still to be analyzed and characterized, on surfaces treated with products 10 made with 80 and 200 mesh Xanthan gum. 5.2 Surface performance – cleaning effect The surface performance of three types of xanthan gum were evaluated (cleaning effect) by applying the formulations of the H line on a marble slab with surface encrustation of iron oxide. 15 Figures 50 and 51 show the visual result before and after treatment (time of application: 2h, 1h and 1h+1h). No substantial differences attributable to the 3 types of rubber were found of Xanthan gum used. 5.3 Adhesion to the substrate in vertical treatments 20 The formulations were tested and applied both on horizontally placed specimens and on cases vertically placed study. Not all formulations showed the same result if placed vertically; for example, in the formulations of the L line, made with 80 mesh Xanthan gum, some sagging phenomena have occurred due to from insufficient adhesive power with the substrate. 25 5.4 Hydrogel viscosity Substantial differences in the viscosity of the final formulations were found, attributable to the different grain size of the Xanthan gum used. For the same formulation, by increasing the grain, an increase in viscosity was observed; especially in the L line, the formulations made with 200 mesh powder, were extremely viscous and compact, making it complex and difficult the application. 5.5 Storage, durability Test# Mesh Creation date Variations Test H5v1 40 10 / 07 / 2023 None Test L5v1 40 10 / 07 / 2023 None After 80 days: formation of similar Test H5v3 80 24 / 07 / 2023 crystals in the gelatinous matrix. After 80 days: slight increase Test L5v3 80 24 / 07 / 2023 of viscosity. After 163 days: formation of Test H4 200 05 / 31 / 2023 crystal-like in the matrix gelatinous. After 80 days: marked increase Test L4 200 05 / 31 / 2023 of viscosity. Table 6 5 5.6 Conclusions Based on the results we have at our disposal to date, the analyses and observations made, the Xanthan gum with a grain size of 40 mesh is found to be the best choice. For both the H and L lines, better performances were found related to: - less surface aggression on the support (more controllable cleaning); 10 - to a better adhesive power which translates into easier applicability in vertical surfaces; - to the different state of aggregation (lower viscosity, therefore fewer problems for the production underway); - to a better chemical stability over time, with consequent improvement of the shelf life. Example 6: Cleaning hydrogel formulation, suitable for application in the field civil, for buildings or civil goods, at pH 4.5. Percentage by weight of weight Component total formulation (% w / w) Tetrasodium glutamate diacetate (Na -GLDA) 3% Citric Acid 3% Isopropanol 2.999% Tridac Iso-3 1% Dipropylene glycol monomethyl ether (DPM) 3% Xanthan gum 5% I have 82.001% Total 100% 5 Note that Example 6 corresponds to test #H5v1 in Examples 1-5. Example 7: Cleaning hydrogel formulation, suitable for application in the field civil, for buildings or civil goods, with neutral pH (7.2). Percentage by weight of weight Component total formulation (% w / w) Tetrasodium glutamate diacetate (Na -GLDA) 3.5% Trisodium dicarboxymethyl alanine (Na -MGDA) 1.6% Citric Acid 1.2% Isopropanol 2.999% Tridac Iso-3 1% Dipropylene glycol monomethyl ether (DPM) 3% Xanthan gum 5% I 81.701% Total 100% Note that Example 7 corresponds to the #L6Neutral test in Examples 1-3. Example 8: Cleaning hydrogel formulation, suitable for application to goods cultural, at pH 6.6. Percentage by weight of weight Total component of the formulation (% p / p) Trisodium dicarboxymethyl alanine (Na -MGDA) 4.65% Citric Acid 1.35% Isopropanol 2.999% Tridac Iso-3 1% Dipropylene glycol monomethyl ether (DPM) 3% Xanthan gum 6% I have 81.001% Total 100% Note that Example 8 corresponds to test #L9v4 in Examples 1-3.

Claims

CLAIMS 1. Hydrogel formulation for cleaning stone surfaces comprising - a first chelating agent consisting of citric acid, - a second chelating agent selected from the group consisting of: Tetrasodium glutamate diacetate, Trisodium dicarboxymethyl alaninate and combinations of the previous, - a supporting agent consisting of xanthan gum, - at least one co-thickener, - at least one surfactant, - at least one antibacterial and / or anti-mold agent, - water, wherein the weight ratio between the sum of the first chelating agent and the second chelating agent and the xanthan gum is between 1:0.7 and 1:1.

6.

2. Formulation according to claim 1, wherein the weight ratio between the sum of the at least one co-thickener and the at least one surfactant and the xanthan gum is between 1:1.2 and 1:

2.

3. Formulation according to claim 1 or 2, wherein the particle size of the xanthan gum is between 30 and 50 mesh.

4. Formulation according to any of claims 1 to 3, wherein the at least one co-thickener is selected from the group consisting of: dipropylene glycol monomethyl ether, dipropopylene glycol dimethyl ether, propylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, dipropylene glycol, and combinations of the preceding.

5. A formulation according to any of claims 1 to 4, wherein the at least one surfactant is selected from the group consisting of: a polyethylene glycol ether of a fatty alcohol, an alkyl polyethylene glycol of a fatty alcohol, an ethoxylated propoxylated fatty alcohol, a polypropylene glycol / polyethylene glycol ether of a hydrogenated fatty alcohol, a polyoxyalkylated fatty alcohol ether, and combinations of the foregoing.

6. Formulation according to any of claims 1 to 5, wherein the at least one antibacterial and / or antimold is selected from the group consisting of: isopropanol, ethanol, phenylethyl alcohol, benzyl alcohol, pentylene glycol, isobutyl alcohol, and combinations of the preceding.

7. Formulation according to any of claims 1 to 6, wherein the pH varies between 4 and 7.

6.

8. Method of applying the formulation according to any of claims 1 to 7 to a stone surface, comprising the steps of a) applying the hydrogel formulation to the stone surface, b) leaving it to act for a time between 15 minutes and 120 minutes, c) removing the hydrogel formulation with water, wherein the aforementioned steps a)-c) are repeated for a number of times n between 1 and 3.

9. Use of the formulation according to any of claims 1 to 7, for cleaning stone surfaces.

10. Use of the formulation according to claim 9, for cleaning stone surfaces of buildings or civil heritage, wherein the second chelating agent is Tetrasodium glutamate diacetate, wherein the weight ratio between the sum of the first chelating agent and the second chelating agent and the xanthan gum is between 1:0.7 and 1:1.35, wherein the pH of the formulation is between 4.1 and 4.5 or between 6.8 and 7.5, or for cleaning stone surfaces of cultural heritage, wherein the second chelating agent is Trisodium dicarboxymethyl alaninate, wherein the weight ratio between the sum of the first chelating agent and the second chelating agent and the xanthan gum is between 1:0.8 and 1:1, wherein the pH of the formulation is between 6.4 and 7.