Conservation of cultural heritage - Methods and materials for cleaning porous inorganic materials

This European Standard provides the guidelines for the choice of the operational cleaning technical specifications in order to optimize the cleaning operation. The fundamental requirements for each specific cleaning method are given as to adapt cleaning works for single specific cases.
The objective of cleaning may consist of removal of any combination of unwanted materials, such as: surface or near-surface materials which constitute a present or future threat to conservation, materials which prevent legibility of the object or are disfiguring by nature, deposits which are judged to be incompatible to the historical nature of the object.

Erhaltung des kulturellen Erbes - Verfahren und Materialien für die Reinigung von porösen inorganischen Materialien

Diese europäische Norm stellt die Leitlinien zur Auswahl der technischen Daten der Reinigung bereit, um das Reinigungsverfahren zu optimieren. Die grundlegenden Anforderungen für jedes spezifische Reinigungsverfahren werden vermittelt, um die Reinigungsarbeiten an spezifische Einzelfälle anpassen zu können.
Die Zielsetzung der Reinigung kann die Entfernung von allen Kombinationen unerwünschter Materialien sein, wie beispielsweise: Oberflächen- oder oberflächennahen Materialien, die eine gegenwärtige oder zukünftige Bedrohung für die Konservierung darstellen, Materialien, die eine Wahrnehmbarkeit des Objekts verhindern oder ihrer Art nach entstellend sind, Ablagerungen, die als unvereinbar mit dem historischen Wesen des Objekts einzustufen sind.

Conservation du patrimoine culturel - Méthodes et produits de nettoyage des matériaux inorganiques poreux

La présente Norme européenne formule des lignes directrices quant au choix des spécifications techniques de nettoyage opérationnel en vue d’optimiser l’opération de nettoyage. Les exigences fondamentales de chaque méthode de nettoyage spécifique sont décrites de manière à permettre l'adaptation des travaux de nettoyage à chaque cas particulier.
Le nettoyage peut avoir pour vocation d’éliminer toute combinaison de matériaux indésirables, par exemple : matériaux de surface ou proches de la surface qui constituent ou constitueront une menace pour la conservation du bien culturel ; matériaux qui altèrent la lisibilité du bien ou qui sont de nature à le défigurer ; dépôts jugés incompatibles avec la nature historique du bien.

Ohranjanje kulturne dediščine - Metode in materiali za čiščenje poroznih anorganskih materialov

Ta evropski standard zagotavlja smernice za izbiro tehničnih specifikacij operativnega čiščenja, s katerimi se optimizira postopek čiščenja. Za prilagoditev čiščenja v posameznih posebnih primerih so podane temeljne zahteve za vsako metodo čiščenja posebej.
Namen čiščenja je lahko odstranitev kakršne koli kombinacije neželenih materialov, kot so: površinski materiali ali materiali blizu površine, ki predstavljajo sedanjo ali prihodnjo nevarnost za ohranjanje, materiali, ki preprečujejo berljivost predmeta ali pa so po naravi deformirani, ostanki, ki so nezdružljivi z zgodovinsko naravo predmeta.

General Information

Status
Published
Public Enquiry End Date
13-Sep-2017
Publication Date
08-Jan-2019
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
03-Jan-2019
Due Date
10-Mar-2019
Completion Date
09-Jan-2019

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.RUR]QLKErhaltung des kulturellen Erbes - Verfahren und Materialien für die Reinigung von porösen inorganischen MaterialienConservation du patrimoine culturel - Méthodes et produits de nettoyage des matériaux inorganiques poreuxConservation of cultural heritage - Methods and materials for cleaning porous inorganic materials97.195GHGLãþLQDItems of art and handicrafts. Cultural property and heritageICS:Ta slovenski standard je istoveten z:EN 17138:2018SIST EN 17138:2019en,fr,de01-marec-2019SIST EN 17138:2019SLOVENSKI

STANDARD
SIST EN 17138:2019
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 17138
December
t r s z ICS
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Conservation of Cultural Heritage æ Methods and materials for cleaning porous inorganic materials Conservation du patrimoine culturel æ Méthodes et produits de nettoyage des matériaux inorganiques poreux

Erhaltung des kulturellen Erbes æ Verfahren und Materialien für die Reinigung von porösen anorganischen Materialien This European Standard was approved by CEN on

t { July
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egulations which stipulate the conditions for giving this European Standard the status of a national standard without any alterationä Upætoædate lists and bibliographical references concerning such national standards may be obtained on application to the CENæCENELEC Management Centre or to any CEN memberä

translation under the responsibility of a CEN member into its own language and notified to the CENæCENELEC Management Centre has the same status as the official versionsä

CEN members are the national standards bodies of Austriaá Belgiumá Bulgariaá Croatiaá Cyprusá Czech Republicá Denmarká Estoniaá Finlandá Former Yugoslav Republic of Macedoniaá Franceá Germanyá Greeceá Hungaryá Icelandá Irelandá Italyá Latviaá Lithuaniaá Luxembourgá Maltaá Netherlandsá Norwayá Polandá Portugalá Romaniaá Serbiaá Slovakiaá Sloveniaá Spainá Swedená Switzerlandá Turkey and United Kingdomä

EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre:
Rue de la Science 23,
B-1040 Brussels

t r s z CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Membersä Refä Noä EN

s y s u zã t r s z ESIST EN 17138:2019
EN 17138:2018 (E) 2

Contents Page European foreword ...................................................................................................................................................... 3 Introduction .................................................................................................................................................................... 4 1 Scope .................................................................................................................................................................... 5 2 Normative references .................................................................................................................................... 5 3 Terms and definitions ................................................................................................................................... 5 4 Requirements and general considerations affecting cleaning decisions ................................... 8 5 Preliminary investigation to optimize cleaning selection process ............................................... 9 5.1 Preliminary survey......................................................................................................................................... 9 5.2 Identification of substrate and characterization of unwanted materials ................................ 10 6 Selection of cleaning methods .................................................................................................................. 11 7 Trial cleaning areas ...................................................................................................................................... 11 8 Cleaning methods ......................................................................................................................................... 12 8.1 Water cleaning ............................................................................................................................................... 12 8.2 Mechanical cleaning ..................................................................................................................................... 22 8.3 Chemical cleaning ......................................................................................................................................... 28 8.4 Physical cleaning ........................................................................................................................................... 42 Annex A (informative)

Aqueous poultices ........................................................................................................ 45 A.1 General.............................................................................................................................................................. 45 A.2 Composition of materials used for poultices ...................................................................................... 45 Annex B (informative)

Abrasive materials and use parameters .............................................................. 48 Annex C (informative)

Solubility parameters of organic solvents ........................................................... 49 Annex D (informative)

Alkaline and acid substances ................................................................................... 54 D.1 Alkali-based compounds ............................................................................................................................ 54 D.2 Acid-based compounds ............................................................................................................................... 54 Annex E (informative)

Chelation and chelating agents ................................................................................ 57 Annex F (informative)

Surfactants....................................................................................................................... 59 Bibliography ................................................................................................................................................................. 60 SIST EN 17138:2019

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European foreword This document (EN 17138:2018) has been prepared by Technical Committee CEN/TC 346 “Conservation of Cultural Heritage”, the secretariat of which is held by UNI. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by June 2019, and conflicting national standards shall be withdrawn at the latest by June 2019. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN shall not be held responsible for identifying any or all such patent rights. This document calls for the use of substances and/or procedures that can be injurious to health if adequate precautions are not taken. It is recommended to read the relevant safety data sheets on the occupational and health hazards of the main chemical constituents of the products before using them. It refers only to technical suitability and this not absolves the user from legal obligations relating to health and safety at any stage. The manufacturer should also provide safety data sheets. According to the CEN-CENELEC Internal Regulations, the national standards organisations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. SIST EN 17138:2019

EN 17138:2018 (E) 4

Introduction Cleaning is the removal of unwanted material from an object surface or near-surface. The surface of an object is cleaned either for conservation and/or maintenance or to improve legibility. A cultural heritage object is irreplaceable and while cleaning is undertaken for object conservation; its effects are irreversible. Failure to consider and address the technical problems which can arise during cleaning may cause irrevocable damage to an object. Cultural Heritage should be cleaned using the least disruptive/invasive procedure possible in order to best preserve it. Furthermore, an inadequate or inappropriate intervention may cause, or increase, future deterioration processes or eliminate materials which are undocumented or which would allow a greater understanding of the history of the object. Materials to be removed may include alteration products of the constituent materials, air particulate pollutants, dust, salt efflorescence; partially or totally soluble encrustations; layers of intentionally applied materials that are either inappropriate or no longer functional; biofilms; lichens; mosses. Cleaning, as a part of the conservation plan, is based on the definition of which materials are to be removed and which materials to be preserved. In order to fulfil this task, the appropriate balance should be found among the following requirements: selectivity, effectiveness and controllability. Before cleaning is carried out, it should be evaluated in terms of effectiveness and potential damage (harmfulness) by the use of trial areas. Evaluation should be continued during the cleaning operations and over the longer terms to monitor the effects of cleaning. This framework document describes the cleaning systems providing a list of technical specifications useful for their selection, evaluation and optimization to allow proper and systematic evaluation. Cleaning methods will be described according to a common structure: a) description; b) technical specifications (factors that define the system to be used); c) variables (factors that end users can adjust, control or change to optimize the process according to surface condition, the type and thickness of material to be removed, etc.); d) advantages; e) disadvantages; f) examples of applications (indicative situations in which the cleaning methods have been found to be effective). This standard presents the methodology and requirements for cleaning particularly applicable to natural stone, ceramics, plaster, mortars and concrete. The presence of sensitive components, which may include certain stone lithologies or paint or other decorations on porous inorganic surfaces, for example, will preclude the use of some of the methods outlined in this document. The example applications given in the standard are indicative of practice and are not exhaustive. The standard is intended to serve as guidance for all conservation professionals (architects, surveyors, conservators/restorers, conservation scientists, curators, etc.) involved in the conservation of objects. The standard is intended as a reference for organizations including government bodies and cultural heritage agencies, with a duty to preserve items of cultural heritage. SIST EN 17138:2019

EN 17138:2018 (E) 5

1 Scope This document provides the guidelines for the choice of the operational cleaning technical specifications in order to optimize the cleaning operation. The fundamental requirements for each specific cleaning method are given as to adapt cleaning works for single specific cases. The objective of cleaning may consist of removal of any combination of unwanted materials, such as: degraded protective coatings, surface or near-surface materials, which constitute a present or future threat to conservation, materials which prevent legibility of the object or are disfiguring by nature, deposits which are judged to be incompatible to the historical nature of the object. 2 Normative references There are no normative references in this document. 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses:

IEC Electropedia: available at http://www.electropedia.org/

ISO Online browsing platform: available at http://www.iso.org/obp 3.1 porous inorganic material material including natural stones, e.g. sandstone, limestone, marble, granite, gneiss, gypsum as well as artificial materials, such as mortar, plaster, brick, ceramics, concrete and others [SOURCE: EN 15801:2009, 3.1, modified] 3.2 object single manifestation of tangible cultural heritage Note 1 to entry: The term object is used in this standard for cultural heritage, both immovable and movable. In specific professional contexts, other terms are used: e.g. artefact, cultural property, item, ensemble, site, building fabric. [SOURCE: EN 15898:2011, 3.1.3] 3.3 specimen part considered representative of the material constituting an object Note 1 to entry: The specimen can have different origins and can be taken from: — materials similar to those constituting the object under study (e.g. stone quarries); — specifically prepared comparative materials e.g. reference materials; — available materials from the object. Note 2 to entry: The number and dimension of the specimens can be different depending on constraints encountered in sampling the required amount of material. [SOURCE: EN 16302:2013, 3.3] SIST EN 17138:2019

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3.4 cleaning removal of unwanted material from an object Note 1 to entry: The criteria for something being “unwanted” can be stated, e.g. potentially damaging, obscuring detail, diminishes aesthetic value, etc. [SOURCE: EN 15898:2011, 3.5.3] 3.5 water cleaning cleaning including a series of different systems using water in liquid or vapour phase 3.6 nebulous spray intermittent mist spray development of low-pressure water washing, characterised by a mist spray entering in contact with the object surface 3.7 water spray at low pressure spray based on the use of water at low pressure 3.8 abrasive cleaning cleaning including all techniques that physically abrade the object surface to remove unwanted materials 3.9 dry grit blasting sandblasting dry blasting process delivering a stream of abrasive particles, under pressure, toward the object surface 3.10 microblasting microsandblasting dry blasting process delivering a thin stream of fine abrasive particles, under pressure, toward the object surface 3.11 wet grit blasting hydro sandblasting blowing of a mixture of water and grit toward the object surface 3.12 peeling system cleaning method consisting of the application of a film forming product which can be peeled off to remove adhered particulate materials 3.13 steam cleaning cleaning method where water vapour is used SIST EN 17138:2019

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3.14 aqueous poultices packs absorbent materials (non-reactive packs) mixed with water to form a paste which is applied to the object surface 3.15 biocide substance able to kill micro-organisms, animals or plants colonizing porous substrates 3.16 biocleaning cleaning using non-pathogenic micro-organisms to remove undesired substances (sulfates, nitrates, organic matter, etc.) from a surface 3.17 chelating agents organic substances forming coordinate bonds with metal ions and producing a stable structure 3.18 cryogenic cleaning dry ice-blasting in a pressurized air stream and directed onto the object surface 3.19 ion exchange resins polymers (essentially) which contain ionic groups linked to their macromolecules by a weak bond and consequently have the ability to inter-exchange these groups with the ions present in the surrounding medium 3.20 laser cleaning cleaning consisting in the removal of the unwanted surface materials from a substrate by using laser irradiation 3.21 surfactant substance which lowers the surface tension of the medium in which it is dissolved, and/or the interfacial tension with other phases, and, accordingly, is positively adsorbed at the liquid/vapour and/or at other interfaces 3.22 toxic substances and preparations which, if they are inhaled or taken internally or if they penetrate the skin, may involve serious, acute or chronic health risks and even death Note 1 to entry: See Directive 67/548/EEC. 3.23 toxicity degree to which a substance is toxic SIST EN 17138:2019

EN 17138:2018 (E) 8

4 Requirements and general considerations affecting cleaning decisions Cleaning should not be carried out unless necessary and when done it should be at the minimum level deemed effective. The cleaning treatment should effectively remove both unwanted materials from the surface and/or in the bulk of the substrate (effectiveness) and should not increase the likelihood of future deterioration (harmfulness). Therefore, to be a “conservation treatment” a cleaning method has to meet the following criteria: a) it should not raise the possibility that reactive chemical compounds have adverse reactions with the materials to be conserved, either immediately or in the future; b) it should not leave permanent or non volatile residues on or inside the object which might be harmful or have the capacity to change the morphology or the colour of the surface (for example efflorescences, stains, halos) either immediately or in the future; c) it should not cause physical - mechanical damage to the object (including erosion, loss of cohesion, detachment or formation of micro-cracks, increase of porosity); d) it should respect the original surface and finishes, and any subsequent additions with artistic or historic value (painting, patination, etc.) and/or original tool marks of the surface; e) it should maintain or, if possible, restore a level of surface topography comparable to that of the original surface; f) it should not be carried out in such way that it endangers the health of building occupants or workers; therefore the possible toxicity of the products shall be taken into account; as well as the possible toxicity of waste requiring removal to appropriate storage sites; g) it should minimize the risk of damage to any personal or public property; h) it should require that due consideration is taken on the practicalities of treatment in order to minimize potential problems with efficiency and application. As no building, no environment, no object, no deterioration history is necessarily identical it is anticipated that solutions will differ. A number of different decay features may occur on an object which necessitates deployment of various methods. Each conservation project should be considered carefully, taking into account previous experience with the object (or similar objects) and available materials and methods which might be useful but should not be assumed to apply fully in every case. Some deposits are not fully removable from surfaces without causing excessive damage. In this case, residual or uneven marks may remain and do not necessarily indicate poor quality cleaning. Methods which allow careful control and evaluation and which may be readily halted by the operator are favoured. The efficacy of each method should be evaluated for each specific situation. Preliminary laboratory tests are intended to define the potential danger as well as the likely effectiveness of the method for each type and condition of porous materials. Special attention should be paid to the chemical and physical nature of the product used, for the cleaning process, the methodology and the duration of the application. Methods and products which are harmless in some cases, may cause damage on other materials or on the same material if applied incorrectly. SIST EN 17138:2019

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In case of well-consolidated materials, cleaning is usually the first operation to be carried out. Where objects are in an advanced state of decay or naturally lack of cohesion, pre-consolidation of the material and protection of the surface with a sheet of Japanese paper prior to cleaning should be considered. It should be noted that such a treatment may influence the eventual choice of the cleaning method, and it may become more difficult to eliminate any biodeteriogens, for example cyanobacteria, algae, lichens and mosses and others unwanted materials deeply penetrated within the substrate. Original paint/decorations should always be retained. In the case of carved surfaces, or any other surfaces of any particular historical and/or artistic importance, scales and fragments of the original surface should be retained in situ, wherever possible, and not deliberately removed. It should be noted also that the end result of cleaning will depend both on the knowledge and capacity of the conservator/restorer, the effectiveness of the materials and methods adopted. 5 Preliminary investigation to optimize cleaning selection process 5.1 Preliminary survey 5.1.1 A preliminary survey should be carried out according to EN 16095 and EN 16096, particularly taking into account the following items: a) historical information of previous conservation intervention (cleaning/treatment); b) description of the nature of the constituent materials and their location on the object by visual inspection, which may include additional investigations where finishes may be present; c) description and mapping of the different forms of deterioration by visual inspection; d) description and localization of the effects of previous cleaning operations and other interventions if they are detectable by visual inspection; e) study of environmental context. A full understanding of the context of the site should be obtained to identify and minimize any environmental decay factors, which may arise from the cleaning process; f) identification of potential test areas; g) background information on susceptibility of substrates as a preliminary guidance for the selection of cleaning methods; h) search for evidence for former paint layers. 5.1.2 Records should be kept of all operations on object of significance including: a) photographs of the object showing its condition and appearance before cleaning is carried out; b) drawings of the different materials constituting the cultural heritage object; c) drawings of unwanted materials location, thickness and nature; and current condition of the object. Specific phenomena should be characterised and a description given with the images to provide an ongoing record. This may be done with reference to an existing visual glossary which should be stated. When non-invasive methods are not available or are unable to provide the necessary information, samples for laboratory analyses should be taken, where possible. These samples are required in order SIST EN 17138:2019

EN 17138:2018 (E) 10

to accurately identify the materials and the deterioration products and consequently to select the most appropriate cleaning method. 5.2 Identification of substrate and characterization of unwanted materials 5.2.1 Following preliminary survey, objects to be cleaned should be inspected closely and analysis/tests should be carried out using the following procedure: a) each constituting material should be identified in sufficient detail so that cleaning can proceed while minimizing risk to the object. The knowledge of the chemical, mineralogical and structural characteristics of the material constituting the object and the properties of the substrate close to the external surface, are important. This is a more accurate assessment of item 5.1.1 b); b) the condition of the object and associated materials should be assessed and mapped (digital record), as well as the nature and effects of previous treatment operations, (see 5.1.1 c) and d); c) the extent, nature, thickness and distribution of materials to be removed should be identified. The layer of unwanted materials and the altered surface of substrate should be distinguished from each other at the investigation stage, so that the level of cleaning can be selected; d) the presence of surface working and or intentional stratification such as finishing, painting and polychrome layers should be identified; e) assessment, by means of preliminary laboratory tests, of the effectiveness and harmfulness over the immediate and long term perspectives of the cleaning products and procedures to be used on similar materials. 5.2.2 Unwanted materials on object surfaces can vary from a few microns to some millimetres in thickness and cleaning can involve removal of one or more of the following materials, reported as the more common examples: a) atmospheric particulates, often bound together as well as to the object surface and composed either of calcium sulfate, calcium carbonate or silica, depending on the substrate; b) biofilms composed by heterotrophic bacteria, cyanobacteria, algae, fungi, lichens; c) mortar splashes and runs; d) encrustations of calcium carbonate; e) efflorescent salts; f) bird droppings; g) paint and graffiti; h) bird repellent gel; i) oils, grease and waxes; j) stains; k) soiling or earth encrustations on archaeological items; SIST EN 17138:2019

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l) overpaints; m) anti-graffiti coatings; n) previous treatments or reaction products derived from previous treatments. 5.2.3 Records should be kept of previous operations on object of significance including drawings (photographs or analyses) of: a) the different materials constituting cultural heritage object if different from 5.1.1 b); b) the extent, nature, thickness and distribution of materials to be removed and of the condition of the object, if different from 5.1.1 c) and d); c) the surface finishes or tool marks, painting and polychrome layers; d) the sampling location, if applicable. Specifications and other documents that might be required for a cleaning project should be prepared in sufficient detail to give a proper guidance in the preparation of estimates and execution of the work. Copies of all relevant documents should be available to all parties involved, including site personnel responsible for supervision. Documents should be retained to provide background information prior to further assessments or work. Following these surveys the decision on which, if any, cleaning methods are appropriate, should be made. 6 Selection of cleaning methods Following the preliminary survey and the identification of the substrate and unwanted materials (see 5.2) an appropriate cleaning method should be selected among those reported in Clause 8. As a cleaning process may involve multiple applications of one system or several removal systems in situ trials should be carried out on representative areas Efficacy and suitability of the products and procedures (see Clause 7) tested, shall be subject to preliminary evaluation. As a single object can consist of a complex assemblage of features differentiated by their physical and chemical properties, the expertise of a team of professionals, each one specialized in a defined field of knowledge may be required to produce a conservation plan which uses several different products and procedures. 7 Trial cleaning areas The aim of cleaning a trial area should be to determine: — the suitability of the cleaning method for the object, its condition, and the unwanted materials; — the degree of cleaning that can be achieved, and its acceptability. Cleaning processes should be pre-tested on surfaces of the object representative of all those on which cleaning will be performed. If possible, test areas should be located in unobtrusive locations, and in any case should be small in case the decision made after the trials is not to proceed with full scale cleaning. When trialling different cleaning methods those which are (seen as / predicted to be) least aggressive shall be tested first. Progression towards methods which are more aggressive should be made only if necessary. SIST EN 17138:2019

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A detailed record should be kept of trial cleaning and the location of trial areas. This should be retained for reference throughout the duration of the cleaning process. Trial cleaning should be observed and assessed by persons responsible for preparing the cleaning specification. Trial areas should be available for inspection by relevant authorities. Trial cleaning should be agreed beforehand, and carried out by trained and experienced specialists conversant in a variety of cleaning systems. When useful, trial areas should be assessed in wet and dry conditions. Full assessment should include: a) potential damage to the object as a result of cleaning; b) colour changes resulting from the cleaning process; c) the general appearance change of the object surface after cleaning; d) the efficacy of the removal of unwanted materials. 8 Cleaning methods 8.1 Water cleaning 8.1.1 General Water cleaning includes a series of different systems using water in liquid or vapour phase. Water can be supplied in different forms as mist of droplets, spray, steam etc. or contained within a gel or poultice medium. The solvent action of water is mainly influenced by temperature and specific surface of the droplets coming into contact with the object surface. In addition to the solvent action a mechanical effect is also present, due to the water contact pressure. If the condition of the surface allows it, the action of the water spray can be augmented by a gentle mechanical action, using, for example, nylon or bristle brushes. Before selection of any one of these methods, the porosity and condition of the material shall be assessed in order to balance the amount of water and duration required. Special consideration should be given to areas where the materials change, for exam

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