One of the most striking but unexplained phenomena in the natural degradation of glass is the tra... more One of the most striking but unexplained phenomena in the natural degradation of glass is the transformation of an almost colorless, transparent and homogeneous glass into a colored, opaque and heterogeneous degradation layer. In many cases, the degradation layer consists of numerous lamellae with a thickness between 0.1 and 10 μm. However, both internal structure and formation process of laminated degradation layers remain unclear. In this paper, a model is proposed where we assume that transformed (degraded) glass consists of a random packing of nano-sized silica particles while the lamellae are the result of different packing densities. The model is able to connect the texture of numerous lamellae observed by several types of microscopic techniques with the structure at molecular level determined by means of chemical analysis. In addition, the model is able to explain numerous properties such as the parameters responsible for the contrast between lamellae. This contrast can be caused by differences in color, density, elemental composition, or surface roughness.
Chrome yellow refers to a group of synthetic inorganic pigments that became popular as an artist'... more Chrome yellow refers to a group of synthetic inorganic pigments that became popular as an artist's material from the second quarter of the 19th century. The color of the pigment, in which the chromate ion acts as a chromophore, is related to its chemical composition (PbCr1-xSxO4, with 0≤x≤0.8) and crystalline structure (monoclinic/orthorhombic). Their shades range from the yellow-orange to the paler yellow tones with increasing sulfate amount. These pigments show remarkable signs of degradation after limited time periods. Pure PbCrO4 (crocoite in its natural form) has a deep yellow color and is relatively stable, while the co-precipitate with lead sulfate (PbCr1-xSxO4) has a paler shade and seems to degrade faster. This degradation is assumed to be related to the reduction of Cr(VI) to Cr(III). We show that on increasing the sulfur(S)-content in chrome yellow, the band gap increases. Typically, when increasing the band gap, one might assume that a decrease in photo activity is the result. However, the photo activity relative to the Cr content, and thus Cr reduction, of sulfur-rich PbCr1-xSxO4 is found to be much higher compared to the sulfur-poor or non-doped lead chromates. This discrepancy can be explained by the evolution of the crystal and electronic structure as function of the sulfur content: first-principles density functional theory calculations show that both the absorption coefficient and reflection coefficients of the lead chromates change as a result of the sulfate doping in such a way that the generation of electron-hole pairs under illumination relative to the total Cr content increases. These changes in the material properties explain why paler shade yellow colors of this pigment are more prone to discoloration. The electronic structure calculations also demonstrate that lead chromate and its co-precipitates are p-type semiconductors, which explains the observed reduction reaction. As understanding this phenomenon is valuable in the field of cultural heritage, this study is the first joint action of photo-electrochemical measurements and first-principles calculations to approve the higher tendency of sulfur-rich lead chromates to darken.
It is commonly known that the conservation state of works of arts exhibited inside museums is str... more It is commonly known that the conservation state of works of arts exhibited inside museums is strongly influenced by the indoor environmental quality (IEQ). Heritage institutions traditionally record and evaluate their IEQ by monitoring temperature, relative humidity, and -more rarely-light. However, smart use of technology enables monitoring other parameters that give a more complete insight in environmental ‘air aggressiveness’. One of this parameters is particulate matter (PM) and especially its concentration, size distribution and chemical composition. In this work, we present a selection of data sets which were obtained in a measuring campaign performed in the War Heritage Institute in Brussels, Belgium. A continuous monitoring of PM concentration with a light scattering based particle counter was performed. In addition the daily mass concentration and size distribution of airborne PM was monitored by means of Harvard impactors. The chemical composition of sampled PM was inferred from the results of XRF and IC analysis. The insights from these datasets are combined with the results of traditional environmental monitoring (temperature, relative humidity and light intensity), and assessed against the recommended guidelines for conservation environments. By using an integrated approach based on the calculation of an IEQ-index, we present a straightforward methodology to evaluate and visualize the IEQ including also continuous PM monitoring. It is clear from the results of this study how including PM in IEQ analysis allows to identify potential risks for museum collections that remain invisible when only traditional parameters are considered.
Historical mixed-media objects consist of a wide range of materials that can be organic and inorg... more Historical mixed-media objects consist of a wide range of materials that can be organic and inorganic in nature. They are often fragile due to the nature of the materials used, and their advanced state of degradation. Well-considered preservation conditions are needed to slow down their degradation. Since each material has its specific requirements, it is challenging to give preventive conservation recommendations. To support the decision making, a risk-based approach is developed. The proposed methodology (1) offers an objective basis to define compromises in preservation conditions, and (2) allows the comparison of different scenarios in order to select the most appropriate one. The methodology is first explained theoretically. Subsequently, its two application aspects are illustrated on the basis of a case study regarding the preventive conservation of a medieval Enclosed Garden.
Naar aanleiding van de installatie van een verwarmingssysteem in de Sint-Martinuskerk van Aalst i... more Naar aanleiding van de installatie van een verwarmingssysteem in de Sint-Martinuskerk van Aalst is een uitgebreide meetcampagne opgestart om de impact van deze installatie op het kerkinterieur te evalueren. Hiervoor zijn verschillende omgevingsparameters gemonitored, en is ook het gedrag van hout opgevolgd. De verwarmingsinstallatie zorgt voor een gemengde verwarming, d.w.z., een constante achtergrondverwarming (10°C) met tijdelijke temperatuursverhoging tijdens erediensten en evenementen om het comfortniveau te verhogen (tot ± 15°C). De verwarming zorgt voor een vrij gelijkmatige warmteverdeling in de kerk, en ook hoogtegradiënten zijn beperkt. Dankzij de verwarming worden periodes van hoge vochtigheid vermeden, waardoor de kans op schimmelgroei sterk vermindert. Tijdens koude, droge periodes buiten moet echter extra aandacht besteed worden aan de regeling om extreem droge condities in de kerk te vermijden. Negatieve effecten van de verwarming zijn de extremere fluctuaties in relatieve vochtigheid, voornamelijk in de frequentie van enkele dagen tot weken. Deze fluctuaties zorgen voor een groot aantal cycli waarin het hout een sterk krimp- en zwelgedrag vertoont. Dit leidt tot spanningen in het hout, en meer algemeen in elk hygroscopisch materiaal, met daardoor een verhoogd schadepotentieel.
We present a decision-support system that guides heritage guardians in selecting mitigation actio... more We present a decision-support system that guides heritage guardians in selecting mitigation actions to improve the indoor air quality and thus the preservation conditions of indoor collections in heritage buildings. This contribution shows that it is feasible to build a decision support system dedicated to preventive conservation when the following barriers are overcome: 1) simultaneous measurement of a wide range of environmental parameters in order to detect a larger number of undesired situations; 2) development of an algorithm to perform reproducible indoor air quality assessments; and 3) transformation of the air quality assessment into a graph that can be read intuitively without causing a wide variation of interpretations among stakeholders. An important aspect of the decision support system is that it reduces several sources of uncertainty that hamper reliable indoor air quality assessments. The possibilities of such a system are illustrated with a measurement campaign in a church where a heating system has been installed and used for the first time.
Heritage-related guidelines and standards recommend stable climatic conditions, since these contr... more Heritage-related guidelines and standards recommend stable climatic conditions, since these contribute to the extension of heritage collections life. As a result, numerous museums and other heritage institutions implement (expensive) mitigation measures to achieve stable conditions. Nevertheless, temperature and relative humidity fluctuations are often still observed. This contribution demonstrates that the analysis of temperature and humidity peaks and drops helps to identify hazards which cause fluctuations in different frequency ranges. This hazard identification provides information on the type of mitigation actions that are required in the near future and in which order they need to be implemented. The approach is illustrated with a case study. A 22 month monitoring campaign was performed in a chapel in the center of Antwerp (Belgium) where the climatic conditions are controlled with a heating, ventilation and air conditioning (HVAC) system. Low-, mid- and high-frequency fluctuations were separated and discussed for their hazards.
Climate change will affect the preservation conditions of our cultural heritage. Therefore, well-... more Climate change will affect the preservation conditions of our cultural heritage. Therefore, well-considered mitigation actions should be implemented to safeguard our heritage for future generations. Environmental monitoring is essential to follow up the change in preservation conditions and to evaluate the effectiveness of performed mitigation actions. To support heritage guardians in the processing and evaluation of monitored data, an indoor air quality (IAQ) index for heritage applications is introduced. The index is calculated for each measured point in time and is visualized in a user-friendly and intuitive way. The current paper describes the backbone of the IAQ-calculating algorithm. The algorithm is subsequently applied on a case study in which a mitigation action is implemented in a church.
IOP Conference Series Materials Science and Engineering, 2018
The exposure of cultural heritage to the environment has a significant impact on its degradation ... more The exposure of cultural heritage to the environment has a significant impact on its degradation process and degradation rate. Consequently, managing the indoor air quality is vital to minimize further damage to historical artefacts and works of art. Despite its potential impact, the traditional assessment of the indoor air quality still represents a challenge for most collection guardians. This approach typically relays on the comparison of measured environmental parameters and corresponding acceptable values. However, determining the acceptable values and relative importance of the different environmental parameters turns out to be quite complex since it depends on the material types present in the collection and their preservation state. Furthermore, the significant amount of data generated during the measurements hampers the application of traditional methods of analysis. Considering all these, we propose the use of data mining as an alternative method for the indoor air quality assessment in cultural heritage studies. Data mining can provide knowledge from vast volumes of heterogeneous data, through high-speed processing, detection, and analysis. Here we present its application to identify dynamics and patterns affecting the indoor air quality in a realistic case. Using data from a measuring campaign held at a late Gothic church in Belgium, we show that inappropriate periods can be identified without using standards. In addition, different types of periods can be identified by studying the relation between multiple parameters. For that we use the k-means clustering method, interpreting the results with both visual and statistical tools.
IOP Conference Series Materials Science and Engineering, 2018
Environmental parameters such as temperature, relative humidity, visible light, UV radiation and ... more Environmental parameters such as temperature, relative humidity, visible light, UV radiation and pollution influence the deterioration rate of heritage items. To judge on the environmental appropriateness for heritage conservation, it is therefore important to monitor the environment. Often, an incomplete set of environmental parameters is measured, or sporadic or time-averaged measurements are performed. As a result, a wide range of undesirable situations and hazards remain unnoticed. This might lead to an underestimation of environmental dangers (i.e., inaccurate judgement) or to inappropriate mitigation measures (i.e., inaccurate decision making). We present an innovative and user-friendly monitoring device that simultaneously and continuously measures (1) environmental parameters and (2) material behavior. An extended combination of off-the-shelf sensors for temperature, relative humidity, air speed, CO2, NO2, O3 and particulate matter are connected to a multipurpose datalogger. In-house developed sensors for the shrinkage and expansion behavior of wood, as well as sensors for metal corrosion rates are connected to the same datalogger. Such extended monitoring shows the identification of a wider range of undesirable situations, and it facilitates the search for correlations between such situations and the sources that cause them, i.e., the hazards.
English ArtGarden Abstract
The ArtGarden research project test and develop an efficient ("best p... more English ArtGarden Abstract
The ArtGarden research project test and develop an efficient ("best practices") matrix (tool - protocol) for monitoring, imaging and documenting (art-technical), fragile historic mixed-media objects. This will be used to facilitate decision making during conservation and preservation practice.
The focus of the project is the guiding and evaluation of conservation treatment and the transportation, display in a museum environment and long-term storage of complex degraded historic multi-media artefacts. Up until now, guidelines have concentrated on one material characteristic. The complex nature of a large number of historic mixed-media artefacts in museum collections is more challenging and less developed. The ArtGarden project is combining documentation, conservation and preservation protocols (Terminology defined by ICOM-CC, New Delhi, 2008) to create an innovative tool to support collection care, maintenance, display and valorization of complex historic collection artefacts. The casus in ArtGarden is the conservation and preservation of the unique collection of seven Enclosed Gardens from the Mechelen City Museums. The 16th-century Enclosed Gardens of the Hospital Sisters of Mechelen, listed as masterpieces by the Flemish ‘Topstukken’ decree, are very rare in Belgian and even world heritage. Most Enclosed Gardens have been lost, mainly due to a lack of interest. This recently changed: these ‘popular retables’ are now considered as testimonies of a 16th-century (women’s) spirituality that by their unique pictorial vernacular give an idea of life in convent communities. They testify to a cultural identity closely connected to mystical traditions. They are a gateway to a lost world, an essential part of culture in the Southern Netherlands.
The Enclosed Gardens or ‘Horti Conclusi’ are extremely fragile heritage objects made of a large variety of materials such as silk, parchment, glass, metals, insignias, paint layers and bones (relics). Many of these materials, either alone or in combination with other materials, are vulnerable to natural ageing through breaking, corroding, fading, etc.
Atmospheric total suspended particulate (TSP)was passively sampled bymeans of deployed horizontal... more Atmospheric total suspended particulate (TSP)was passively sampled bymeans of deployed horizontal and vertical filters in various rooms of four Belgian cultural heritage buildings, installed with various heating/ventilation systems. Soiling/blackening and deposition of inorganic, water-soluble aerosol components were considered. The extent of soiling was determined by means of two independent methods: (1) in terms of the covering rate of the samplers by optical reflection microscopy and (2) the reduction in lightness of the samplers using the CIE L*a*b* color space by spectrophotometry. A fairly good correlation was found between both methods. The inorganic composition of the deposited water-soluble TSP was quantified by means of ion chromatography. Compared to controlled environments, uncontrolled environments showed increased water-soluble aerosol content of the total deposited mass. Higher chloride deposition was observed on horizontal surfaces, compared to vertical surfaces.
Several artists' pigments are semiconductors. Some of these materials appear stable over time, wh... more Several artists' pigments are semiconductors. Some of these materials appear stable over time, whereas others already show remarkable signs of degradation after limited time periods. The (in)stability of these pigments can be understood using a thermodynamic approach. For several pigment-related materials, the thermodynamic oxidation and reduction potential (f ox and f red ) were determined and evaluated considering the absolute energy positions of the valence and conduction band edges and the water redox potentials. The positions of f ox and f red can be used in a fast screening of the stability of semiconductor pigments towards photoinduced corrosion in an aqueous/humid environment. This theoretical approach corresponds well with experimental data on pigment permanence and degradation phenomena found in literature.
Chemical transformations in paintings often induce discolorations, disturbing the appearance of t... more Chemical transformations in paintings often induce discolorations, disturbing the appearance of the image. For an appropriate conservation of such valuable and irreplaceable heritage objects, it is important to have a good know-how on the degradation processes of the (historical) materials: which pigments have been discolored, what are the responsible processes, and which (environmental) conditions have the highest impact on the pigment degradation and should be mitigated. Pigment degradation is already widely studied, either by analyzing historical samples or by accelerated weathering experiments on dummies. However, in historic samples several processes may have taken place, increasing the complexity of the current state, while aging experiments are time-consuming due to the often extended aging period. An alternative method is proposed for a fast monitoring of degradation processes of semiconductor pigments, using an electrochemical setup mimicking the real environment and allowi...
The Science of the total environment, Jan 15, 2015
Atmospheric total suspended particulate (TSP) was passively sampled by means of deployed horizont... more Atmospheric total suspended particulate (TSP) was passively sampled by means of deployed horizontal and vertical filters in various rooms of four Belgian cultural heritage buildings, installed with various heating/ventilation systems. Soiling/blackening and deposition of inorganic, water-soluble aerosol components were considered. The extent of soiling was determined by means of two independent methods: (1) in terms of the covering rate of the samplers by optical reflection microscopy and (2) the reduction in lightness of the samplers using the CIE L*a*b* color space by spectrophotometry. A fairly good correlation was found between both methods. The inorganic composition of the deposited water-soluble TSP was quantified by means of ion chromatography. Compared to controlled environments, uncontrolled environments showed increased water-soluble aerosol content of the total deposited mass. Higher chloride deposition was observed on horizontal surfaces, compared to vertical surfaces.
It is well known that airborne particulate matter (APM) has an impact on our cultural heritage. A... more It is well known that airborne particulate matter (APM) has an impact on our cultural heritage. A limited number of articles have been published on the sequential application of elemental and molecular techniques to estimate the degradation potential of APM in environments of cultural heritage importance, and most of these were concerned with indoor environments. The Alhambra monument (Granada, Spain) represents one of the grandest and finest examples of Islamic art and architecture from the Middle Ages. As part of an air quality investigation, two sets of APM were collected at the Hall of the Ambassadors and characterised to determine its potential degradation profile. These were analysed by means of micro-Raman spectroscopy (MRS) and electron probe microanalysis with X-ray detection (EPXMA). The Raman data indicated the presence of various mixed salts of acidic and/or hygroscopic nature, such as sodium and ammonium nitrates and sulfates, especially in the finer fraction. Automated EPXMA estimated this fraction to be as high as 50%. Apart from the potential chemical attack, the soiling due to carbonaceous matter deposition is a real concern. Soot was identified by MRS and EPXMA in all size fractions, reaching values of up to 55%, and was often intertwined with soluble inorganic salts. Ongoing degradation of the pigments is implicated by the presence of brightly coloured particles. MRS and molar abundance ternary diagrams elicited the chemical structure of individual APM so that the degradation potential could be established.
Environmental Science and Pollution Research, 2013
In the 1970s, a large ambulatory of the National Tile Museum, Lisbon, was closed with glass panes... more In the 1970s, a large ambulatory of the National Tile Museum, Lisbon, was closed with glass panes on both ground and first floor. Although this design was meant to protect the museum collection from ambient air pollutants, small openings between the glass panes remain, creating a semi-enclosed corridor. The effects of the glass panes on the indoor air quality were evaluated in a comparative study by monitoring the airborne particle concentration and the extent of particle deposition at the enclosed corridor as well as inside the museum building. Comparison of the indoor/outdoor ratio of airborne particle concentration demonstrated a high natural ventilation rate in the enclosed corridor as well as inside the museum building. PM 10 deposition velocities on vertical surfaces were estimated in the order of 3 × 10 −4 m s −1 for both indoor locations. Also, the deposition rates of dark-coloured and black particles in specific were very similar at both indoor locations, causing visual degradation. The effectiveness of the glass panes in protecting the museum collection is discussed.
One of the most striking but unexplained phenomena in the natural degradation of glass is the tra... more One of the most striking but unexplained phenomena in the natural degradation of glass is the transformation of an almost colorless, transparent and homogeneous glass into a colored, opaque and heterogeneous degradation layer. In many cases, the degradation layer consists of numerous lamellae with a thickness between 0.1 and 10 μm. However, both internal structure and formation process of laminated degradation layers remain unclear. In this paper, a model is proposed where we assume that transformed (degraded) glass consists of a random packing of nano-sized silica particles while the lamellae are the result of different packing densities. The model is able to connect the texture of numerous lamellae observed by several types of microscopic techniques with the structure at molecular level determined by means of chemical analysis. In addition, the model is able to explain numerous properties such as the parameters responsible for the contrast between lamellae. This contrast can be caused by differences in color, density, elemental composition, or surface roughness.
Chrome yellow refers to a group of synthetic inorganic pigments that became popular as an artist'... more Chrome yellow refers to a group of synthetic inorganic pigments that became popular as an artist's material from the second quarter of the 19th century. The color of the pigment, in which the chromate ion acts as a chromophore, is related to its chemical composition (PbCr1-xSxO4, with 0≤x≤0.8) and crystalline structure (monoclinic/orthorhombic). Their shades range from the yellow-orange to the paler yellow tones with increasing sulfate amount. These pigments show remarkable signs of degradation after limited time periods. Pure PbCrO4 (crocoite in its natural form) has a deep yellow color and is relatively stable, while the co-precipitate with lead sulfate (PbCr1-xSxO4) has a paler shade and seems to degrade faster. This degradation is assumed to be related to the reduction of Cr(VI) to Cr(III). We show that on increasing the sulfur(S)-content in chrome yellow, the band gap increases. Typically, when increasing the band gap, one might assume that a decrease in photo activity is the result. However, the photo activity relative to the Cr content, and thus Cr reduction, of sulfur-rich PbCr1-xSxO4 is found to be much higher compared to the sulfur-poor or non-doped lead chromates. This discrepancy can be explained by the evolution of the crystal and electronic structure as function of the sulfur content: first-principles density functional theory calculations show that both the absorption coefficient and reflection coefficients of the lead chromates change as a result of the sulfate doping in such a way that the generation of electron-hole pairs under illumination relative to the total Cr content increases. These changes in the material properties explain why paler shade yellow colors of this pigment are more prone to discoloration. The electronic structure calculations also demonstrate that lead chromate and its co-precipitates are p-type semiconductors, which explains the observed reduction reaction. As understanding this phenomenon is valuable in the field of cultural heritage, this study is the first joint action of photo-electrochemical measurements and first-principles calculations to approve the higher tendency of sulfur-rich lead chromates to darken.
It is commonly known that the conservation state of works of arts exhibited inside museums is str... more It is commonly known that the conservation state of works of arts exhibited inside museums is strongly influenced by the indoor environmental quality (IEQ). Heritage institutions traditionally record and evaluate their IEQ by monitoring temperature, relative humidity, and -more rarely-light. However, smart use of technology enables monitoring other parameters that give a more complete insight in environmental ‘air aggressiveness’. One of this parameters is particulate matter (PM) and especially its concentration, size distribution and chemical composition. In this work, we present a selection of data sets which were obtained in a measuring campaign performed in the War Heritage Institute in Brussels, Belgium. A continuous monitoring of PM concentration with a light scattering based particle counter was performed. In addition the daily mass concentration and size distribution of airborne PM was monitored by means of Harvard impactors. The chemical composition of sampled PM was inferred from the results of XRF and IC analysis. The insights from these datasets are combined with the results of traditional environmental monitoring (temperature, relative humidity and light intensity), and assessed against the recommended guidelines for conservation environments. By using an integrated approach based on the calculation of an IEQ-index, we present a straightforward methodology to evaluate and visualize the IEQ including also continuous PM monitoring. It is clear from the results of this study how including PM in IEQ analysis allows to identify potential risks for museum collections that remain invisible when only traditional parameters are considered.
Historical mixed-media objects consist of a wide range of materials that can be organic and inorg... more Historical mixed-media objects consist of a wide range of materials that can be organic and inorganic in nature. They are often fragile due to the nature of the materials used, and their advanced state of degradation. Well-considered preservation conditions are needed to slow down their degradation. Since each material has its specific requirements, it is challenging to give preventive conservation recommendations. To support the decision making, a risk-based approach is developed. The proposed methodology (1) offers an objective basis to define compromises in preservation conditions, and (2) allows the comparison of different scenarios in order to select the most appropriate one. The methodology is first explained theoretically. Subsequently, its two application aspects are illustrated on the basis of a case study regarding the preventive conservation of a medieval Enclosed Garden.
Naar aanleiding van de installatie van een verwarmingssysteem in de Sint-Martinuskerk van Aalst i... more Naar aanleiding van de installatie van een verwarmingssysteem in de Sint-Martinuskerk van Aalst is een uitgebreide meetcampagne opgestart om de impact van deze installatie op het kerkinterieur te evalueren. Hiervoor zijn verschillende omgevingsparameters gemonitored, en is ook het gedrag van hout opgevolgd. De verwarmingsinstallatie zorgt voor een gemengde verwarming, d.w.z., een constante achtergrondverwarming (10°C) met tijdelijke temperatuursverhoging tijdens erediensten en evenementen om het comfortniveau te verhogen (tot ± 15°C). De verwarming zorgt voor een vrij gelijkmatige warmteverdeling in de kerk, en ook hoogtegradiënten zijn beperkt. Dankzij de verwarming worden periodes van hoge vochtigheid vermeden, waardoor de kans op schimmelgroei sterk vermindert. Tijdens koude, droge periodes buiten moet echter extra aandacht besteed worden aan de regeling om extreem droge condities in de kerk te vermijden. Negatieve effecten van de verwarming zijn de extremere fluctuaties in relatieve vochtigheid, voornamelijk in de frequentie van enkele dagen tot weken. Deze fluctuaties zorgen voor een groot aantal cycli waarin het hout een sterk krimp- en zwelgedrag vertoont. Dit leidt tot spanningen in het hout, en meer algemeen in elk hygroscopisch materiaal, met daardoor een verhoogd schadepotentieel.
We present a decision-support system that guides heritage guardians in selecting mitigation actio... more We present a decision-support system that guides heritage guardians in selecting mitigation actions to improve the indoor air quality and thus the preservation conditions of indoor collections in heritage buildings. This contribution shows that it is feasible to build a decision support system dedicated to preventive conservation when the following barriers are overcome: 1) simultaneous measurement of a wide range of environmental parameters in order to detect a larger number of undesired situations; 2) development of an algorithm to perform reproducible indoor air quality assessments; and 3) transformation of the air quality assessment into a graph that can be read intuitively without causing a wide variation of interpretations among stakeholders. An important aspect of the decision support system is that it reduces several sources of uncertainty that hamper reliable indoor air quality assessments. The possibilities of such a system are illustrated with a measurement campaign in a church where a heating system has been installed and used for the first time.
Heritage-related guidelines and standards recommend stable climatic conditions, since these contr... more Heritage-related guidelines and standards recommend stable climatic conditions, since these contribute to the extension of heritage collections life. As a result, numerous museums and other heritage institutions implement (expensive) mitigation measures to achieve stable conditions. Nevertheless, temperature and relative humidity fluctuations are often still observed. This contribution demonstrates that the analysis of temperature and humidity peaks and drops helps to identify hazards which cause fluctuations in different frequency ranges. This hazard identification provides information on the type of mitigation actions that are required in the near future and in which order they need to be implemented. The approach is illustrated with a case study. A 22 month monitoring campaign was performed in a chapel in the center of Antwerp (Belgium) where the climatic conditions are controlled with a heating, ventilation and air conditioning (HVAC) system. Low-, mid- and high-frequency fluctuations were separated and discussed for their hazards.
Climate change will affect the preservation conditions of our cultural heritage. Therefore, well-... more Climate change will affect the preservation conditions of our cultural heritage. Therefore, well-considered mitigation actions should be implemented to safeguard our heritage for future generations. Environmental monitoring is essential to follow up the change in preservation conditions and to evaluate the effectiveness of performed mitigation actions. To support heritage guardians in the processing and evaluation of monitored data, an indoor air quality (IAQ) index for heritage applications is introduced. The index is calculated for each measured point in time and is visualized in a user-friendly and intuitive way. The current paper describes the backbone of the IAQ-calculating algorithm. The algorithm is subsequently applied on a case study in which a mitigation action is implemented in a church.
IOP Conference Series Materials Science and Engineering, 2018
The exposure of cultural heritage to the environment has a significant impact on its degradation ... more The exposure of cultural heritage to the environment has a significant impact on its degradation process and degradation rate. Consequently, managing the indoor air quality is vital to minimize further damage to historical artefacts and works of art. Despite its potential impact, the traditional assessment of the indoor air quality still represents a challenge for most collection guardians. This approach typically relays on the comparison of measured environmental parameters and corresponding acceptable values. However, determining the acceptable values and relative importance of the different environmental parameters turns out to be quite complex since it depends on the material types present in the collection and their preservation state. Furthermore, the significant amount of data generated during the measurements hampers the application of traditional methods of analysis. Considering all these, we propose the use of data mining as an alternative method for the indoor air quality assessment in cultural heritage studies. Data mining can provide knowledge from vast volumes of heterogeneous data, through high-speed processing, detection, and analysis. Here we present its application to identify dynamics and patterns affecting the indoor air quality in a realistic case. Using data from a measuring campaign held at a late Gothic church in Belgium, we show that inappropriate periods can be identified without using standards. In addition, different types of periods can be identified by studying the relation between multiple parameters. For that we use the k-means clustering method, interpreting the results with both visual and statistical tools.
IOP Conference Series Materials Science and Engineering, 2018
Environmental parameters such as temperature, relative humidity, visible light, UV radiation and ... more Environmental parameters such as temperature, relative humidity, visible light, UV radiation and pollution influence the deterioration rate of heritage items. To judge on the environmental appropriateness for heritage conservation, it is therefore important to monitor the environment. Often, an incomplete set of environmental parameters is measured, or sporadic or time-averaged measurements are performed. As a result, a wide range of undesirable situations and hazards remain unnoticed. This might lead to an underestimation of environmental dangers (i.e., inaccurate judgement) or to inappropriate mitigation measures (i.e., inaccurate decision making). We present an innovative and user-friendly monitoring device that simultaneously and continuously measures (1) environmental parameters and (2) material behavior. An extended combination of off-the-shelf sensors for temperature, relative humidity, air speed, CO2, NO2, O3 and particulate matter are connected to a multipurpose datalogger. In-house developed sensors for the shrinkage and expansion behavior of wood, as well as sensors for metal corrosion rates are connected to the same datalogger. Such extended monitoring shows the identification of a wider range of undesirable situations, and it facilitates the search for correlations between such situations and the sources that cause them, i.e., the hazards.
English ArtGarden Abstract
The ArtGarden research project test and develop an efficient ("best p... more English ArtGarden Abstract
The ArtGarden research project test and develop an efficient ("best practices") matrix (tool - protocol) for monitoring, imaging and documenting (art-technical), fragile historic mixed-media objects. This will be used to facilitate decision making during conservation and preservation practice.
The focus of the project is the guiding and evaluation of conservation treatment and the transportation, display in a museum environment and long-term storage of complex degraded historic multi-media artefacts. Up until now, guidelines have concentrated on one material characteristic. The complex nature of a large number of historic mixed-media artefacts in museum collections is more challenging and less developed. The ArtGarden project is combining documentation, conservation and preservation protocols (Terminology defined by ICOM-CC, New Delhi, 2008) to create an innovative tool to support collection care, maintenance, display and valorization of complex historic collection artefacts. The casus in ArtGarden is the conservation and preservation of the unique collection of seven Enclosed Gardens from the Mechelen City Museums. The 16th-century Enclosed Gardens of the Hospital Sisters of Mechelen, listed as masterpieces by the Flemish ‘Topstukken’ decree, are very rare in Belgian and even world heritage. Most Enclosed Gardens have been lost, mainly due to a lack of interest. This recently changed: these ‘popular retables’ are now considered as testimonies of a 16th-century (women’s) spirituality that by their unique pictorial vernacular give an idea of life in convent communities. They testify to a cultural identity closely connected to mystical traditions. They are a gateway to a lost world, an essential part of culture in the Southern Netherlands.
The Enclosed Gardens or ‘Horti Conclusi’ are extremely fragile heritage objects made of a large variety of materials such as silk, parchment, glass, metals, insignias, paint layers and bones (relics). Many of these materials, either alone or in combination with other materials, are vulnerable to natural ageing through breaking, corroding, fading, etc.
Atmospheric total suspended particulate (TSP)was passively sampled bymeans of deployed horizontal... more Atmospheric total suspended particulate (TSP)was passively sampled bymeans of deployed horizontal and vertical filters in various rooms of four Belgian cultural heritage buildings, installed with various heating/ventilation systems. Soiling/blackening and deposition of inorganic, water-soluble aerosol components were considered. The extent of soiling was determined by means of two independent methods: (1) in terms of the covering rate of the samplers by optical reflection microscopy and (2) the reduction in lightness of the samplers using the CIE L*a*b* color space by spectrophotometry. A fairly good correlation was found between both methods. The inorganic composition of the deposited water-soluble TSP was quantified by means of ion chromatography. Compared to controlled environments, uncontrolled environments showed increased water-soluble aerosol content of the total deposited mass. Higher chloride deposition was observed on horizontal surfaces, compared to vertical surfaces.
Several artists' pigments are semiconductors. Some of these materials appear stable over time, wh... more Several artists' pigments are semiconductors. Some of these materials appear stable over time, whereas others already show remarkable signs of degradation after limited time periods. The (in)stability of these pigments can be understood using a thermodynamic approach. For several pigment-related materials, the thermodynamic oxidation and reduction potential (f ox and f red ) were determined and evaluated considering the absolute energy positions of the valence and conduction band edges and the water redox potentials. The positions of f ox and f red can be used in a fast screening of the stability of semiconductor pigments towards photoinduced corrosion in an aqueous/humid environment. This theoretical approach corresponds well with experimental data on pigment permanence and degradation phenomena found in literature.
Chemical transformations in paintings often induce discolorations, disturbing the appearance of t... more Chemical transformations in paintings often induce discolorations, disturbing the appearance of the image. For an appropriate conservation of such valuable and irreplaceable heritage objects, it is important to have a good know-how on the degradation processes of the (historical) materials: which pigments have been discolored, what are the responsible processes, and which (environmental) conditions have the highest impact on the pigment degradation and should be mitigated. Pigment degradation is already widely studied, either by analyzing historical samples or by accelerated weathering experiments on dummies. However, in historic samples several processes may have taken place, increasing the complexity of the current state, while aging experiments are time-consuming due to the often extended aging period. An alternative method is proposed for a fast monitoring of degradation processes of semiconductor pigments, using an electrochemical setup mimicking the real environment and allowi...
The Science of the total environment, Jan 15, 2015
Atmospheric total suspended particulate (TSP) was passively sampled by means of deployed horizont... more Atmospheric total suspended particulate (TSP) was passively sampled by means of deployed horizontal and vertical filters in various rooms of four Belgian cultural heritage buildings, installed with various heating/ventilation systems. Soiling/blackening and deposition of inorganic, water-soluble aerosol components were considered. The extent of soiling was determined by means of two independent methods: (1) in terms of the covering rate of the samplers by optical reflection microscopy and (2) the reduction in lightness of the samplers using the CIE L*a*b* color space by spectrophotometry. A fairly good correlation was found between both methods. The inorganic composition of the deposited water-soluble TSP was quantified by means of ion chromatography. Compared to controlled environments, uncontrolled environments showed increased water-soluble aerosol content of the total deposited mass. Higher chloride deposition was observed on horizontal surfaces, compared to vertical surfaces.
It is well known that airborne particulate matter (APM) has an impact on our cultural heritage. A... more It is well known that airborne particulate matter (APM) has an impact on our cultural heritage. A limited number of articles have been published on the sequential application of elemental and molecular techniques to estimate the degradation potential of APM in environments of cultural heritage importance, and most of these were concerned with indoor environments. The Alhambra monument (Granada, Spain) represents one of the grandest and finest examples of Islamic art and architecture from the Middle Ages. As part of an air quality investigation, two sets of APM were collected at the Hall of the Ambassadors and characterised to determine its potential degradation profile. These were analysed by means of micro-Raman spectroscopy (MRS) and electron probe microanalysis with X-ray detection (EPXMA). The Raman data indicated the presence of various mixed salts of acidic and/or hygroscopic nature, such as sodium and ammonium nitrates and sulfates, especially in the finer fraction. Automated EPXMA estimated this fraction to be as high as 50%. Apart from the potential chemical attack, the soiling due to carbonaceous matter deposition is a real concern. Soot was identified by MRS and EPXMA in all size fractions, reaching values of up to 55%, and was often intertwined with soluble inorganic salts. Ongoing degradation of the pigments is implicated by the presence of brightly coloured particles. MRS and molar abundance ternary diagrams elicited the chemical structure of individual APM so that the degradation potential could be established.
Environmental Science and Pollution Research, 2013
In the 1970s, a large ambulatory of the National Tile Museum, Lisbon, was closed with glass panes... more In the 1970s, a large ambulatory of the National Tile Museum, Lisbon, was closed with glass panes on both ground and first floor. Although this design was meant to protect the museum collection from ambient air pollutants, small openings between the glass panes remain, creating a semi-enclosed corridor. The effects of the glass panes on the indoor air quality were evaluated in a comparative study by monitoring the airborne particle concentration and the extent of particle deposition at the enclosed corridor as well as inside the museum building. Comparison of the indoor/outdoor ratio of airborne particle concentration demonstrated a high natural ventilation rate in the enclosed corridor as well as inside the museum building. PM 10 deposition velocities on vertical surfaces were estimated in the order of 3 × 10 −4 m s −1 for both indoor locations. Also, the deposition rates of dark-coloured and black particles in specific were very similar at both indoor locations, causing visual degradation. The effectiveness of the glass panes in protecting the museum collection is discussed.
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Papers by Willemien Anaf
The ArtGarden research project test and develop an efficient ("best practices") matrix (tool - protocol) for monitoring, imaging and documenting (art-technical), fragile historic mixed-media objects. This will be used to facilitate decision making during conservation and preservation practice.
The focus of the project is the guiding and evaluation of conservation treatment and the transportation, display in a museum environment and long-term storage of complex degraded historic multi-media artefacts. Up until now, guidelines have concentrated on one material characteristic. The complex nature of a large number of historic mixed-media artefacts in museum collections is more challenging and less developed. The ArtGarden project is combining documentation, conservation and preservation protocols (Terminology defined by ICOM-CC, New Delhi, 2008) to create an innovative tool to support collection care, maintenance, display and valorization of complex historic collection artefacts. The casus in ArtGarden is the conservation and preservation of the unique collection of seven Enclosed Gardens from the Mechelen City Museums.
The 16th-century Enclosed Gardens of the Hospital Sisters of Mechelen, listed as masterpieces by the Flemish ‘Topstukken’ decree, are very rare in Belgian and even world heritage. Most Enclosed Gardens have been lost, mainly due to a lack of interest. This recently changed: these ‘popular retables’ are now considered as testimonies of a 16th-century (women’s) spirituality that by their unique pictorial vernacular give an idea of life in convent communities. They testify to a cultural identity closely connected to mystical traditions. They are a gateway to a lost world, an essential part of culture in the Southern Netherlands.
The Enclosed Gardens or ‘Horti Conclusi’ are extremely fragile heritage objects made of a large variety of materials such as silk, parchment, glass, metals, insignias, paint layers and bones (relics). Many of these materials, either alone or in combination with other materials, are vulnerable to natural ageing through breaking, corroding, fading, etc.
filters in various rooms of four Belgian cultural heritage buildings, installed with various heating/ventilation
systems. Soiling/blackening and deposition of inorganic, water-soluble aerosol components were considered. The
extent of soiling was determined by means of two independent methods: (1) in terms of the covering rate of the
samplers by optical reflection microscopy and (2) the reduction in lightness of the samplers using the CIE L*a*b*
color space by spectrophotometry. A fairly good correlation was found between both methods. The inorganic composition
of the deposited water-soluble TSP was quantified by means of ion chromatography. Compared to controlled
environments, uncontrolled environments showed increased water-soluble aerosol content of the total
deposited mass. Higher chloride deposition was observed on horizontal surfaces, compared to vertical surfaces.
The ArtGarden research project test and develop an efficient ("best practices") matrix (tool - protocol) for monitoring, imaging and documenting (art-technical), fragile historic mixed-media objects. This will be used to facilitate decision making during conservation and preservation practice.
The focus of the project is the guiding and evaluation of conservation treatment and the transportation, display in a museum environment and long-term storage of complex degraded historic multi-media artefacts. Up until now, guidelines have concentrated on one material characteristic. The complex nature of a large number of historic mixed-media artefacts in museum collections is more challenging and less developed. The ArtGarden project is combining documentation, conservation and preservation protocols (Terminology defined by ICOM-CC, New Delhi, 2008) to create an innovative tool to support collection care, maintenance, display and valorization of complex historic collection artefacts. The casus in ArtGarden is the conservation and preservation of the unique collection of seven Enclosed Gardens from the Mechelen City Museums.
The 16th-century Enclosed Gardens of the Hospital Sisters of Mechelen, listed as masterpieces by the Flemish ‘Topstukken’ decree, are very rare in Belgian and even world heritage. Most Enclosed Gardens have been lost, mainly due to a lack of interest. This recently changed: these ‘popular retables’ are now considered as testimonies of a 16th-century (women’s) spirituality that by their unique pictorial vernacular give an idea of life in convent communities. They testify to a cultural identity closely connected to mystical traditions. They are a gateway to a lost world, an essential part of culture in the Southern Netherlands.
The Enclosed Gardens or ‘Horti Conclusi’ are extremely fragile heritage objects made of a large variety of materials such as silk, parchment, glass, metals, insignias, paint layers and bones (relics). Many of these materials, either alone or in combination with other materials, are vulnerable to natural ageing through breaking, corroding, fading, etc.
filters in various rooms of four Belgian cultural heritage buildings, installed with various heating/ventilation
systems. Soiling/blackening and deposition of inorganic, water-soluble aerosol components were considered. The
extent of soiling was determined by means of two independent methods: (1) in terms of the covering rate of the
samplers by optical reflection microscopy and (2) the reduction in lightness of the samplers using the CIE L*a*b*
color space by spectrophotometry. A fairly good correlation was found between both methods. The inorganic composition
of the deposited water-soluble TSP was quantified by means of ion chromatography. Compared to controlled
environments, uncontrolled environments showed increased water-soluble aerosol content of the total
deposited mass. Higher chloride deposition was observed on horizontal surfaces, compared to vertical surfaces.