SIST EN 17488:2021

SLOVENSKI STANDARD
01-september-2021
Ohranjanje kulturne dediščine - Postopek za analitično vrednotenje pri izbiri
metod za čiščenje poroznih anorganskih materialov, uporabljenih pri tej kulturni
dediščini
Conservation of cultural heritage - Procedure for the analytical evaluation to select
cleaning methods for porous inorganic materials used in cultural heritage
Erhaltung des kulturellen Erbes - Methodologie für die analytische Prüfung zur Auswahl
von Reinigungsverfahren von porösen anorganischen Objekten des kulturellen Erbes
Conservation du patrimoine culturel - Procédure pour l'évaluation analytique et le choix
des méthodes de nettoyage des matériaux inorganiques poreux dans les bâtiments
d'intérêt patrimonial
Ta slovenski standard je istoveten z: EN 17488:2021
ICS:
97.195 Umetniški in obrtniški izdelki. Items of art and handicrafts.
Kulturne dobrine in kulturna Cultural property and
dediščina heritage
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 17488
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2021
EUROPÄISCHE NORM
ICS 97.195
English Version
Conservation of cultural heritage - Procedure for the
analytical evaluation to select cleaning methods for porous
inorganic materials used in cultural heritage
Conservation du patrimoine culturel - Procédure pour Erhaltung des kulturellen Erbes - Methodologie für die
l'évaluation analytique et le choix des méthodes de analytische Prüfung zur Auswahl von
nettoyage des matériaux inorganiques poreux dans les Reinigungsverfahren von porösen anorganischen
bâtiments d'intérêt patrimonial Objekten des kulturellen Erbes
This European Standard was approved by CEN on 23 May 2021.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 17488:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Abbrevations. 9
5 General procedure (Part A) . 9
5.1 Overview . 9
5.2 Identification of substrate and characterization of unwanted materials. 10
5.3 Selection of suitable cleaning methods to be tested . 11
5.4 Localization, delimitation and numbering of the cleaning trial areas . 11
5.5 Design of the evaluation procedure and definition of a referenced cleaned area . 12
6 On site surface investigations . 15
6.1 Optical observation . 15
6.1.1 Portable digital microscope . 15
6.1.2 Raking light . 15
6.1.3 Portable digital stereo microscope . 15
6.1.4 Fluorescence induced by UV radiation . 15
6.2 Chemical/physical analysis . 16
6.2.1 Measurement of colour . 16
6.2.2 Elemental analysis by portable XRF . 16
6.2.3 Molecular analysis by portable FTIR . 16
6.2.4 Surface ion analysis . 16
6.3 Water absorption assessment . 17
6.3.1 General . 17
6.3.2 Determination of water absorption by pipe method (in situ) . 17
6.3.3 Determination of water absorption by contact sponge method (in situ) . 17
6.3.4 Water drop test (in situ) . 17
7 Laboratory analysis on samples taken from trial areas . 18
7.1 General . 18
7.2 Sampling . 18
7.3 Chemical/physical analysis . 19
7.3.1 Examinations of fragments surfaces by TLOM, RLOM, SEM/ESEM and EDS
microanalysis . 19
7.3.2 Examinations of thin and polished and cross section by TLOM, RLOM, SEM/ESEM and
EDS microanalysis . 20
7.3.3 Vibrational spectroscopy (FTIR, micro-FTIR and Raman) . 20
7.4 Surface morphology analysis . 20
7.4.1 Measurement of roughness (see ISO 25178) . 20
7.5 Wet chemical analysis (on aqueous extract) in the case of chemical cleaning . 21
7.5.1 Extraction procedure . 21
7.5.2 Analysis on aqueous extract . 23
8 Overall evaluation of results obtained . 23
9 Analytical procedure for testing methods under development on specimens of
analogous material (Part B). 24
9.1 General procedure . 24
9.2 Preparation of test specimens . 26
9.2.1 Number and dimensions of test specimens . 26
9.2.2 Pre-conditioning of test specimens . 27
9.3 Evaluation process of the cleaning method(s) under test . 27
9.4 Test analysis on specimens before and after the application of cleaning methods . 27
9.4.1 General . 27
9.4.2 Determination of water absorption by capillarity . 27
9.4.3 Colour measurement of surfaces . 28
9.4.4 Observation of the surfaces by the stereo microscope . 28
9.4.5 Determination of mass variation . 28
9.4.6 Thin and polished cross sections analysis by TLOM, RLOM, SEM/ESEM-EDS . 28
9.4.7 Thin and polished cross sections analysis by TLOM, RLOM, SEM/ESEM-EDS on
fragments of surfaces . 29
9.4.8 Cleaning application . 29
9.5 Analysis of aqueous extract for chemical cleaning . 30
9.6 Test report . 30
9.6.1 General information . 30
9.6.2 Results of measurements on specimens . 30
Annex A (normative) Examples of trial applications . 33
Annex B (informative) Test carried out, findings, inference . 38
Annex C (informative) Specifications to be reported for different cleaning methods (see
EN 17138:2018) . 48
Bibliography . 52

European foreword
This document (EN 17488:2021) 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 December 2021, and conflicting national standards shall
be withdrawn at the latest by December 2021.
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.
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, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United
Kingdom.
Introduction
Cleaning is the removal of unwanted material from an object surface or near-surface.
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 an object.
The actions required for cleaning involve a degree of risk for the object and therefore demand extreme
caution. The chosen methods for cleaning should not be harmful to the object, the operator, the
surroundings /environment, or users of the site.
Cleaning operation needs to take into account the compatibility definition (EN 15898) as the “extent to
which one material can be used with another material without putting significance or stability at risk”.
Extending the definition of compatibility to the cleaning action a “compatibility analysis” should therefore
ascertain how cleaning actions (in terms of effectiveness and harmfulness) would impact on the
significance and stability of the heritage object.
A successful cleaning strategy needs to adher to the strategy for the whole conservation-project in
accordance with the conservation-process and the condition report (EN 16853, EN 16085 and EN 16095)
and requires careful consideration of a number of aspects which include but are not limited to:
— the significance of the object;
— the aim of the cleaning;
— a clear definition of the nature of the materials to be removed and the rationale;
— context and sensitivity of the object to be evaluated (for example presence of polychrome and gilt
surfaces);
— condition of the substrate, which may result in greater risk of harm during testing;
— form of the substrate (flat or carved surface).
These factors may exclude the use of one or more cleaning methods, which would be unsuitable.
This document takes into account the extreme variability of both the constituent materials and the
conditions of the object, prescribing a procedure of analytical tests and comparing the extent of possible
damage, which may result from each cleaning method tested.
“Harmfulness” indicates the level of risk of the variety of unwanted changes, which may appear not only
in short-term but also in long-term after cleaning.
This may include the deterioration of the substrate, the change of porosity or surface roughness, the
release of residual substances and formation of stains, which are not compatible with the material and or
which could interfere with future conservation intervention.
The potential harmfulness of a cleaning method may be greater when it is applied to a deteriorated
material.
Evaluation of effectiveness and potential harmfulness of cleaning methods need to be carried out on site
by establishing a “trial area” as a preliminary step before any extensive work is started.
The process of cleaning requires careful evaluation throughout the work. This is initiated at the primary
evaluation through the execution of trials and continues with the monitoring and optimization during the
selected process. Trials aim to identify the method(s) of cleaning which produce an acceptable result at
minimum risk to the object. Even an extensive sampling procedure may fail to identify all the conditions
which exist on a cultural object therefore ongoing evaluation of the cleaning and the effects on the
substrate are vital. If necessary, cleaning needs to be halted to re-appraise the methods used or to
undertake further testing where areas of increased sensitivity or uncertainty are uncovered. This
document identifies the means by which cleaning methods may be selected and evaluated as part of
conservation interventions.
Unwanted interactions may arise from different substrate and cleaning method combinations. Some
features of a given substrate may cause it to be particularly damaged depending on the method and
circumstances of its use. These specific combinations will increase likelihood of damage. In some
circumstances the synergistic effects can be easily predicted, e.g. a salt-laden wall masonry may be
seriously affected by a water-based method, even if we know that generally this cleaning method is gentle
and of low aggressiveness. The assessment of the synergistic effects should take into consideration that
damage may emerge after some considerable elapsed time.
The initial assessment for a building or similar immovable object will take place on site with non-invasive
systems. If necessary, it may be followed by appropriate micro-invasive or invasive laboratory analysis
(Figure 1, Table 1).
As there are many different cleaning methods and the results can vary greatly it is necessary to carefully
evaluate any proposed technique/system before trial and subsequent application. Reference to standard
EN 17138 is required to undertake this.
Cleaning methods considered in EN 17138 were divided into four categories: Water cleaning, mechanical
cleaning, physical cleaning and chemical cleaning. Each method requires different considerations in order
to select the most appropriate investigations.
Assessment of harmfulness for chemical cleaning methods needs additional investigation with respect to
the possible interactions between the chemicals and the products to be removed, notably the formation
of by-products which could be harmful for the substrate. As a consequence, the procedure for chemical
cleaning will follow a different pathway (Figures 2 and 6, Table 1).
The document is composed of two parts:
a) General procedure (Part A) to be applied when the evaluation of the effects of cleaning of a cultural
heritage object surface is needed.
b) Analytical procedure (Part B) for testing cleaning methods under development on specimens of
analogous material similarly decayed.
Cleaning methods and materials, which are under development should not be evaluated on cultural
heritage objects surface but they should be tested according to the analytical procedure described in
part B.
1 Scope
This document gives the test methodology for evaluation of both harmfulness and effectiveness of a
cleaning method as applied to porous inorganic materials. Mural paintings and polychromy are excluded.
Evaluation includes the use of on-site analyses and/or laboratory studies.
The evaluation of the potential harm has a higher priority than the effectiveness in order to prevent
overcleaning. It is important that cleaning is always at the minimum level deemed effective and that it
respects the original surface and finishes. Overcleaning is a term used to indicate that irreversible damage
has been done by the unnecessary removal of materials, which are part of the value of the object.
This document applies to:
a) Part A: all methods of cleaning, which have characteristics of parameterization and reproducibility
(see EN 17138).
b) Part B: all new methods that are under development.
This document applies to evaluate the optimum methods for cleaning and the optimization of the
parameters of the selected cleaning process.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 15801, Conservation of cultural property - Test methods - Determination of water absorption by
capillarity
EN 15886, Conservation of cultural property - Test methods - Colour measurement of surfaces
EN 16095, Conservation of cultural property - Condition recording for movable cultural heritage
EN 16096, Conservation of cultural property - Condition survey and report of built cultural heritage
EN 16302, Conservation of cultural heritage - Test methods - Measurement of water absorption by pipe
method
EN 16455, Conservation of cultural heritage - Extraction and determination of soluble salts in natural stone
and related materials used in and from cultural heritage
EN 16515:2015, Conservation of Cultural Heritage - Guidelines to characterize natural stone used in
cultural heritage
EN 17138:2018, Conservation of Cultural Heritage - Methods and materials for cleaning porous inorganic
materials
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 https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
cleaning effectiveness
ability to remove unwanted material
3.2
harmfulness
any undesired change in the substrate to be cleaned, except the removal of the unwanted material
3.3
invasive analysis
requires the removal of powder or of a fragment from the surface or from the bulk of the object
3.4
micro-invasive analysis
no visible damage on the surface
Note 1 to entry: A small amount of material is collected (1 mg or less).
3.5
non-invasive analysis
contact between object surface and apparatus used for measurements is avoided; no material is removed
from the object
3.6
sample
portion of material, ideally representative, removed from the cultural property for scientific investigation
[SOURCE: EN 16085:2012, 3.2]
3.7
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);
— reference materials, for instance, specifically prepared comparative materials;
— available materials from the object.
Note 2 to entry: The number and dimension of the specimens can be different depending on difficulties
encountered in sampling the required amount of material.
[SOURCE: EN 15886:2010, 3.11]
3.8
trial area
location where the cleaning method under evaluation is tested
3.9
unwanted material
substances to be removed indicated by the conservation plan
4 Abbrevations
The following list of analytical techniques is considered:
4.1 UVF: Fluorescence induced by Ultraviolet Radiation
4.2 pXRF: Portable X Ray Fluorescence
4.3 TLOM: Transmitted Light Optical Microscopy
4.4 RLOM: Reflected Light Optical Microscopy
4.5 UVOM: Ultraviolet Optical Microscopy
4.6 ESEM/SEM: Environmental Scanning Electron Microscopy/Scanning Electron Microscopy
4.7 WDS: Wavelength Dispersive Spectroscopy
4.8 EDS: Energy Dispersive Spectroscopy
4.9 FTIR: Fourier Transform Infrared Spectroscopy
4.10 Raman: Raman Spectroscopy
4.11 IC: Ion Chromatography
4.12 pH-m: pH measurement
4.13 WDT: Water Drop Test
5 General procedure (Part A)
5.1 Overview
Before starting to evaluate cleaning methods, a condition survey and a condition report are needed in
accordance with standards EN 16095 and EN 16096.
The initial assessment for a building or similar immovable object should take place on site with non-
invasive systems. Successively, if necessary, it may be followed by appropriate micro-invasive or invasive
laboratory analysis (Figure 1, Table 1).
To facilitate the analytical evaluation of cleaning methods in each individual case the following systematic
procedure is proposed. It consists of a number of consecutive stages as described in the flow chart of
Figure 1. Due to the wide variability of each individual case, the whole sequence proposed shall be case
specific and is up to the responsibility of the professional in charge.
Evaluation procedures depend also on time available and resources (budget and staff). In all cases, the
outcome should be the best possible one for the object.
Figure 1 — Flow chart of the procedure for cleaning evaluation
5.2 Identification of substrate and characterization of unwanted materials
The chemical, mineralogical and the micro-structural characteristics of the material constituting the
object shall be known or preliminarily identified (EN 16515) as well as the extent, nature and thickness
of the unwanted materials to be removed.
The layer of unwanted materials and the altered surface of substrate shall be distinguished from each
other at the investigation stage, so that the required degree of cleaning can be determined (see
EN 17138:2018, 5.2).
The preliminary investigations using non-invasive systems should be carried out on a defined trial area
selected as representative of the main surface material composition and cleaning problem.
The main non-invasive systems to be considered are:
a) portable microscope for optical observations;
b) portable XRF equipment for the identification of chemical elements;
c) portable fluorescence induced by UV radiation equipment for the identification of fluorescent
compounds;
d) portable FTIR spectrometer especially in the presence of organic materials.
For laboratory investigations the procedure reported in EN 16515 (examination of specimens under
stereo-microscope, petrographic examination, mineralogical analysis by X-ray diffraction XRD,
examination by SEM/ESEM, chemical analysis) shall be performed.
The identification of organic components, not considered in EN 16515, shall be performed by FTIR
spectroscopy and when necessary by GC-MS (gas chromatography and mass spectrometry).
5.3 Selection of suitable cleaning methods to be tested
As some cleaning methods are inappropriate where painted finishes are present, their presence or
absence shall be established before any evaluation is started.
After the identification of the substrate and of the composition of unwanted materials a selection of
suitable cleaning methods, according to the results obtained, is carried out on the “trial area”.
For the application of this document the following cleaning method categories are considered (see
EN 17138):
a) water cleaning (restricted to the following: nebulous spray or intermittent mist spray, water spray
at low pressure, steam cleaning, aqueous poultices or packs with absorbent material);
b) mechanical cleaning (restricted to the following: micro blasting, wet jet micro blasting, cryogenic
cleaning);
c) chemical cleaning (application of organic solvents, application of acidic or alkaline solutions,
application of chelating agents, application of surfactants, gel cleaning, application of ion exchange
resins);
d) physical cleaning (laser cleaning);
e) those cleaning methods not adjustable by changing physical known parameters (such as cleaning
with a lancet or a brush) are excluded by the present standard.
5.4 Localization, delimitation and numbering of the cleaning trial areas
Trial areas should be selected in order to be representative of the whole (constituting materials, surfaces
and materials to be removed); if possible, trial areas should be unobtrusive. The trial areas should be the
minimum size possible, taking into account the selected cleaning method, the significance of the object
and the evaluation procedure, while still being representative.
The trial area(s) selection process should also take into account:
— the decay patterns, the type of substrate and the nature of unwanted material;
— the object size;
— the number of trial test required;
— the location where the impact of cleaning trials has the least detriment to the significance of the
object, in case the trial should over-clean or otherwise damage an area;
— further optimization of the parameters of the selected cleaning process.
The description of trial areas selection and procedure is reported in Annex A, which is normative.
5.5 Design of the evaluation procedure and definition of a referenced cleaned area
The evaluation procedure is based on the investigations which are described in Clauses 6 and 7, which
shall be carried out before and after cleaning respectively. The tests are also used to establish the level of
cleaning that needs to be achieved and the actual level that can be achieved.
A flow chart of observations and analyses is reported in Figure 2 and Table 1.
The whole sequence reported is the ideal pathway for evaluation of potential harmfulness and
effectiveness of cleaning methods tested in the trial areas. The adaptation of the procedure depends on
specific features of the case (or object) under evaluation and is the responsibility of the professional in
charge. Any variation shall be specified in the test report.
Investigation and interpretation of results shall be performed by professional(s) (e.g. conservation or
material scientists, conservators/restorers) with appropriate competencies.
For most projects this will require a multidisciplinary approach.
The evaluation should be carried out before and soon after the cleaning operation. Monitoring over time
is also possible, taking into account that decay, particulate deposition and several other phenomena can
complicate the interpretation of results strictly referable to cleaning.
For some special cleaning methods an evaluation is also possible in real time during cleaning, such as the
case for Laser Cleaning.
The trial area showing the most suitable result according to all the partners, taking into account the
results of the evaluation (in situ and/or in the laboratory) should be preserved.
This area should be used as the visual reference of the expected cleaning result during all the cleaning
campaign.
Figure 2 — Flow chart of observations and analysis related to cleaning methods
Table 1 — Observations and analysis in relation to the different cleaning categories
Water Mechanical Chemical
a
cleaning /physical
cleaning
cleaning
6 On site surface investigations
6.1 Optical observation
6.1.1 Portable digital microscope X X X
6.1.2 Raking light X X X
6.1.3 Portable digital stereo microscope X X X
6.1.4 Fluorescence induced by UV radiation X X X
6.2 Chemical/physical analysis
6.2.1 Measurement of colour X X X
6.2.2 Elemental analysis by portable XRF X X X
6.2.3 Molecular analysis by portable FTIR X X X
6.2.4 Surface ion analysis X X X
6.3 Water absorption assessment X X X
6.3.2 Determination of water absorption by X X X
pipe method
6.3.3 Determination of water absorption by X X X
contact sponge method
6.3.4 Water drop test X X X
7 Laboratory analysis on samples
7.3.1 TLOM, RLOM and SEM/ESEM-EDS on X X X
fragments
7.3.2 TLOM, RLOM and SEM/ESEM-EDS on thin X X X
cross section
7.3.3 Vibrational spectroscopy (FTIR, micro- X X X
FTIR and Raman)
7.4 Surface morphology analysis (roughness) X X X
7.5 Wet chemical analysis (on aqueous
extract)
7.5.2.2 Specific conductivity measurement X X
7.5.2.3 pH measurement X X
7.5.2.4 Ion content measurement X X
a
Chemical cleaning is considered separately from the other methods due to the potential for
deleterious reactions between chemicals and the unwanted materials to be removed.
Some significant examples of potential drawbacks or side effects are listed below:
i) water cleaning can affect variations in distribution and concentrations of soluble salts (if present);
ii) mechanical cleaning can affect the roughness of the surface with possible change in colour,
appearance and the water absorption behaviour;
iii) physical cleaning can cause discolouration of the surface;
iv) chemical cleaning can affect variations of pH, conductivity and concentrations of soluble salts.
Chemical cleaning methods, which provoke the formation of harmful by-products (e.g. soluble salts
residues, acidic substances etc.), shall generally be avoided.
In particular some of the chemicals mentioned in EN 17138 shall be carefully monitored during in situ
trial tests. We refer to:
a) strong alkaline and acid compounds, which were used in the past but are not commonly currently
used for cultural heritage objects. Substances in the pH range between 5,5 and 8,0 are commonly
used. A notable exception to this regard is the use of ammonium carbonate or bicarbonate (at pH
between 8 and 10), which have been successfully used for many years particularly on limestones and
marbles affected by gypsum formation crusts and on surfaces affected by proteinaceous residues,
oily and greasy materials;
b) chelating agents used at the right pH (between 6 and 10) can be very selective, very effective and
generally not harmful. In the case of painted surfaces pH shall not be above 8, which is the critical
threshold limit for the dissolution of some of the most common pigments;
+
c) strong acid cationic resins release H which can affect calcareous-based materials;
−
d) strong basic anionic resins release OH , which can affect pigments sensitive to an alkaline
environment.
As a consequence of the previous considerations for chemical cleaning it is of importance to monitor any
change of pH and by-product formation as a result of the selected cleaning process.
In addition to the common tests for each of the cleaning methods (water, mechanical and physical
cleaning) an aqueous extract should be obtained and the following measurements shall be carried out on
it:
i) pH;
ii) specific conductivity;
iii) qualitative and quantitative analyses of soluble salts.
6 On site surface investigations
6.1 Optical observation
6.1.1 Portable digital microscope
With the help of a portable digital microscope, it is possible to observe the surface (stone, mortars,
painting layers, finishes) and the decay products. This pre-test could help to optimize sampling. It also
assists in assessment of the results of the cleaning tests and how the different systems affect the surface
morphology, in the preliminary studies and during the development of the restoration works. It is
possible to use several magnifications and specific lights (visible, ultraviolet) to characterize different
surfaces and identify also residues and overpaints.
Acquisition of digital images shall be obtained in order to document the surface condition and also close
observation of residues.
6.1.2 Raking light
Light directed under a very small incidence angle (usually between 5 ° and 20 °) to the object surface
emphasizes its surface morphology and its relief variations. This observation provides information on
the initial condition of the surface (roughness, surface defects etc.) before cleaning tests and any changes
after the cleaning. The observations on target areas shall be photographed under any appropriate
magnification and lighting angle.
6.1.3 Portable digital stereo microscope
The stereo microscope surface observations before and after treatment shall be carried out on the
selected surface area of the object.
The observation points of the surfaces shall be the same before and after treatment. For each observation
point, at least a micro-photograph, shall be acquired including the scale for each magnification. A final
report shall contain qualitative assessments on any visible changes in the surface morphology
accompanied by photos of comparison of individual points of view.
Any type of morphological variation is indicative of a potential damage caused to the surface by the
cleaning method.
6.1.4 Fluorescence induced by UV radiation
This photographic technique is a non-invasive and portable method of analysis of objects of art. It is
usually used for identification of varnishes, protective treatments, binders and repainting, so it can be
very useful in assessing the efficacy of successive cleaning phases.
Ultraviolet fluorescence can be acquired by using the proper source(s) (UV emission around 365 nm) and
a camera equipped with filter able to cut reflected ultraviolet from the surface and environment. In
general, the fluorescence signal is not very intense and therefore the light in the environment should be
almost absent. For each area, at least one photograph before and after cleaning shall be acquired with the
same configuration.
6.2 Chemical/physical analysis
6.2.1 Measurement of colour
The colorimetric measurements are performed according to EN 15886. The surface to be measured
should, as far as practicable, be smooth and flat so as to exclude external light. Where no smooth, flat
areas are available, this shall be noted in the report.
The number and location of measurement points and their diameter shall be adapted to the object as to
obtain statistically representative values. Five measurements at arbitrary locations would be considered
the minimum, however more may be needed.
The measuring points shall be the same before and after treatment. If, following the cleaning, there are
areas with noticeable colour variations, which were not initially measured, they should be quantified and
identified in the photographic documentation.
A few examples of the use of this technique are listed as follows:
— changes in the lightness can be used for assessing the effectiveness of removal of black crusts or
carbonaceous black deposits from substrates light in colour;
— changes in hue could be an indicator of the presence of unwanted chemical reactions. These changes
can result from the reaction of cleaning product with the material to be removed or from the
mobilization of iron soluble compounds causing yellow or brown staining.
6.2.2 Elemental analysis by portable XRF
Portable X-ray fluorescence is an elemental technique able to detect elements on the surface or sub-
surfaces (depending on the matrices) and therefore can be used to trace elements that are characteristic
of material to be removed. This can be done by measuring the same area before and after the cleaning
test. Limitations of the technique shall be taken into account in the evaluation of the results: i) the error
in the detection of lighter elements and ii) the possible peaks overlap (i.e. sulphur in presence of lead or
titanium in presence of barium).
6.2.3 Molecular analysis by portable FTIR
Vibrational spectroscopic patterns can be recorded on a chosen area, before and after cleaning
operations. FTIR is especially indicated to detect the removal of organic layers, although it is of use in
other cases. In case of using a portable FTIR instrument, spectra will be recorded in reflectance mode.
Where the instrument is used on the scaffolding, it is crucial to ensure good stability and to avoid
vibrations to the instruments, which need to be focused precisely.
6.2.4 Surface ion analysis
Plasticized strips test with specific zones of reaction may be used, to detect ions derived from soluble
salts. Normally these are immersed in a solution to identify if a specific ion is present, and the strip
changes colour at varying grades according to the quantity of ions. In the latter case they can be used on
site by placing a wetted reagent strip directly against an efflorescence. Obviously, the result in this case
is qualitative not quantitative and relates only to the outer surface in contact with the strip. Each type of
strip test is sensitive to only one type of ion.
The sensitivity of the strip tests varies according to the type of ion; there is a marked variation in range
between one ion and another (e.g. sulphates 200 ppm to 1 600 ppm (mg/l); nitrates 10 ppm to 500 ppm).
Colorimetric kits (based on colorimetric comparison of a standard coloured scale) can also be used on
site, for their simplicity but require a sample collection. These are based on reactions that lead to the
formation of coloured compounds formed between each ion and its specific reagent. All the reagents and
equipment necessary for analysis are inside the kit together with the instructions for their use. In this
case the intensity of the colour indicates the amount of ions present in the solution and provides a colour
card against which to measure the sample.
6.3 Water absorption assessment
6.3.1 General
It could be important to evaluate the absorption property of the substrate by an appropriate method, as
water absorption, suitable to investigate whether a material surface is porous and absorbent, wettable
but impervious, or hydrophobic. Such properties depend on the substrate nature and condition, and also
on ancient treatments or deposits.
Three alternative methods for water absorption measurements are available (6.3.2, 6.3.3, 6.3.4).
The trial surface should be dry and it should not be exposed to direct solar light or rain. It is recommended
to record temperature (T) and relative humidity (RH) close to the test surface.
...