Deterioration Patterns: Difference between revisions

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== Introduction  ==
== Introduction  ==


Well documented and well analyzed deterioration patterns are of great importance for the assessment of new damage. This collection provides an overview of deterioration patterns, that have been observed in the different material groups.
Well documented and well analyzed deterioration patterns are of great importance for the assessment of new damage. This article provides an overview of deterioration patterns, that have been observed in the different material groups.
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* [[Building Materials]]
* [[Building Materials]]
* [[Wall Painting]]
* [[Deterioration Patterns Wallpaintings|Wall Paintings]]


== Glossary of Salt Efflorescences  ==
== Glossary of Salt Efflorescences  ==


Efflorescences are whitish, powdery or whisker-like crystals on the surface of porous materials. In most cases efflorescences are poorly cohesive and commonly they are made of soluble salt crystals.


On wall paintings, mortar, plaster, ceramic and natural stone, efflorescences repeatedly display certain typical forms. These are briefly characterized, as follows:  
Efflorescences are whitish, powdery or whisker-like crystals on the surface of porous materials. In most cases efflorescences are poorly cohesive and in general they are constituted by soluble salt crystals. On wall paintings, mortar, plaster, ceramic and natural stone, efflorescences repeatedly display certain typical forms. These are briefly characterized as follows:  
[[file:Arnold-Swi 04.jpg|thumb|right|200px|Whiskers are long, thin, sometimes curved crystals, here NaCl whiskers (from <bib id="Arnold.etal:1991"/>)]]


'''Whisker''': a few microns thick to centimeters long, columnar, often curved crystals. Under specific conditions, crystals, which do not typically exhibit needle-building habits, grow like fine, hair-shaped individuals, the so-called whiskers. Whiskers have been observed in a variety of substances, metals, salts and other compounds. Their diameters are between 0.01 and 100 micron, while their length can reach up to a few centimeters. They grow preferentially in the longitudinal direction, while the growth on the lateral crystal plane is either suppressed or, to some extent, still in progress. Some whiskers accommodate a single, or a few, screw dislocations along their axis, causing a spiral growth at the tip, whereupon the material along the lateral plane has to be transported to the tip. There are also whiskers without screw dislocations, where the preferred growth takes place at the top- caused by a different mechanism. Finally, there are whiskers that do not grow at the top, but at their base, pushing the growing crystal upwards.  
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'''Whiskers''': a few microns thick to centimeters long, columnar, often curved crystals. Under specific conditions, crystals, which do not typically exhibit needle-building habits, grow as fine, hair-like shapes, the so-called whiskers. Whiskers have been observed developing from a variety of substances, e.g., metals, salts, etc. Their diameters range between 0.01 and 100 microns, while their length can reach up to a few centimeters. They grow preferentially in the longitudinal direction, while the growth on the lateral crystal plane is either suppressed or, to some extent, still in progress. Some whiskers accommodate a single, or a few, screw dislocations along their axis, causing a spiral growth at the tip, so that material along the lateral plane has to be transported to the tip. Some whiskers do not have screw dislocations, where the preferred growth takes place at the top- caused by a different mechanism. Finally, there are whiskers that do not grow at the top, but at their base, pushing the growing crystal upwards.  
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[[file:Arnold-Swi 04.jpg|thumb|left|400px|Whiskers are long, thin, sometimes curved crystals, here NaCl whiskers (from <bib id="Arnold.etal:1991"/>)]]
 
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<br> '''Feathery - Fluffy efflorescence''':  very loose, fluffy or cotton-like efflorescence, usually consisting of bent whiskers.
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[[file:KNO3-SalzflaumKoenigslutter.jpg|thumb|right|200px|Efflorescence made of KNO<sub>3</sub>, the crystals are whiskers]]
[[file:KNO3-SalzflaumKoenigslutter.jpg|thumb|left|400px|Efflorescence made of KNO<sub>3</sub>, the crystals are whiskers]]
<br> '''Plumose crystals- Fluffy efflorescence''':  very loose, fluffy or cotton-like efflorescence, usually consisting of bent whiskers.


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[[file:IdensenThenardit_ausbluehung_aussen.jpg|thumb|right|200px|Salt crystals on a masonry joint; the individual crystals are whiskers]]
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'''Acicular crystals-bristly efflorescence''': loose columnar whiskers, more or less perpendicular to the surface, 0.1 to several millimeters long, often only visible in raking light.
'''Acicular crystals-bristly efflorescence''': loose columnar whiskers, more or less perpendicular to the surface, 0.1 to several millimeters long, often only visible in raking light.
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[[file:IdensenThenardit_ausbluehung_aussen.jpg|thumb|left|right|400px|Salt crystals on a masonry joint; the individual crystals are whiskers]]


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[[file:Eilsumpudrigeausbluehungen.jpg|thumb|200px|Powdery efflorescences of sodium sulfate]]
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'''Powdery efflorescence''': white, mealy, loose to dense or fluffy coat. Powdery efflorescences depend on the salt type. Some salts, especially the less soluble ones, such as gypsum, can bloom from the beginning in this very fine crystalline form. When sodium sulfate is present, this form of efflorescence can be a dehydration product of the once water-containing salt.  
'''Powdery efflorescence''': white, mealy, loose to dense or fluffy coating. Powdery efflorescence will develop differently depending on the type of salt crystallizing. Some salts, especially the less soluble ones such as gypsum, can bloom in this very fine form as soon as they crystallize. However, in the case of sodium sulfate this form of efflorescence results from the dehydration of the originally hydrated salt.  
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[[file:Eilsumpudrigeausbluehungen.jpg|thumb|left|400px|Powdery efflorescences of sodium sulfate]]


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[[file:Salzpusteln.jpg|thumb|200px|Salt-induced pustules on a wall painting]]
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'''Salt pustules''': separate, loose to compact salt crystals, to about 1 mm diameter.  
'''Salt pustules''': separate, loose to compact salt crystals, to about 1 mm diameter.  
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[[file:Salzpusteln.jpg|thumb|left|400px|Salt-induced pustules on a wall painting]]


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[[file:Treppe_bei_St.Andreas_Hildesheim_Salzkruste.jpg|thumb|200px|Salt crust caused by de-icing salt]]
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'''Salt crust''' : crusts can be formed by soluble salts when they are highly concentrated developing salt aggregates with planar cohesion and very variable thicknesses (a few microns to mm)
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[[file:Treppe_bei_St.Andreas_Hildesheim_Salzkruste.jpg|thumb|left|400px|Salt crust caused by de-icing salt]]


'''Salt crust''' : Crust composed of soluble salts, which develop in the presence of high salt levels,  salt aggregates with planar cohesion and of very different thickness (a few microns to mm)
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[[file:Strahlsund Kochsalz-Kruste.jpg|thumb|200px| Halit crust on an exterior wall in Stahlsund]]
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'''White loose crust''' (sugary crust): It consists of units that are visible to the naked eye or low magnification as glass-clear crystals. Sugary crusts usually form in a moisture film. However, they can crystallize from a salt efflorescence that takes up water from the surrounding air, then goes into solution and crystallizes again in a dry climate.
'''White loose crust''' (sugary crust): consists of individuals that are visible to the naked eye or low magnification as glass-clear crystals. Sugary crusts usually form in a moisture film. However, they can crystallize from a salt efflorescence that takes up water from the surrounding air, undergoing dissolution and followed by recrystallizing as the environment dries.
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[[file:Strahlsund Kochsalz-Kruste.jpg|thumb|left|400px| Halite crust on an exterior wall in Strahlsund]]


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[[file:REM Seidenglanzkruste-mittel.jpg|thumb|200px|SEM photo of a satin like crust]]
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'''Satin Crust''': Flat, shiny crust of salt. Thick, shiny crusts of gypsum are formed only by repeated recrystallization and over longer periods of time.  
'''Satin crust''': flat, shiny crust of salt. Thick, shiny crusts of gypsum are formed only by repeated recrystallization cycles over longer periods of time.  
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[[file:REM Seidenglanzkruste-mittel.jpg|thumb|left|400px|SEM photo of a satin like crust]]


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'''Framboidal or botroidal crusts''': crust of white, spherical aggregates- its surface resembles that of a raspberry or blackberry or even a cauliflower. Botroidal crusts occur preferentially along small defects (e.g., cracks) on an otherwise relatively dense plaster surface. They also can form as separate units on dense stones.
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[[file:Gips Blumenkohlkruste 2.jpg|thumb|left|400px|Framboidal efflorescences]]


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[[file:Gips Blumenkohlkruste 2.jpg|thumb|200px|Cauliflower - like efflorescences]]
'''Cauliflower crusts''': Crust of white, spherical aggregates- its surface resembles that of a cauliflower. Cauliflower crusts occur preferentially along small defects (e. g.. cracks) on an otherwise relatively dense plaster surface.
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'''Fibrous crust:''' Crust made of whiskers, densely packed, perpendicular to the substrate. They arise usually on moist substrates.  
'''Fibrous crust:''' crust composed of densely packed whiskers, perpendicular to the substrate. They usually develop on moist substrates.  


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== Habit  ==
== Habit  ==


*The crystal habit describes the proportions and existing shape of crystals.  
*The crystal habit describes the proportions and shape of crystals.  


<br> The habit of minerals changes subject to the conditions of their formation.  
<br> The habit of salts will change depending on the conditions during their formation.  


Due to the crystal structure and the typical mineral and surface combinations, minerals change in their physical appearance. Variously, changes can also be caused by unilateral growth. We describe these mineral forms as follows:  
Due to the crystal structure and the typical mineral and surface combinations, salts change in their physical appearance. On occasions, changes can also be caused by unilateral growth. We describe these mineral forms as follows:  


*'''isometric''' forms, if the development into all three spatial directions is approximately the same size e.g. for all cubic crystals  
*'''isometric''' forms, if the development into all three spatial directions is approximately of the same size e.g.. all cubic crystals.
*'''one-dimensional elongated''' forms: columnar, acicular, hair-like (whisker), fibrous, such as tourmaline, rutile, asbestos  
*'''one-dimensional elongated''' forms: columnar, acicular, hair-like (whisker), fibrous, such as tourmaline, rutile, asbestos.
*'''two-dimensional elongated''' forms: tabular, lamellar, foliated, scaly, micaceous, e. g. Barite and mica
*'''two-dimensional elongated''' forms: tabular, lamellar, foliated, scaly, micaceous, e.g.. barite and mica.
*'''dendritic''' forms occur in the case of an incomplete crystal growth, developing plant-like shapes   
*'''dendritic''' forms occur in the case of an incomplete crystal growth, developing plant-like shapes.  


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== Formation of salt crystals, according to Arnold  ==
== Formation of salt crystals, according to Arnold  ==


According to <bib id="Arnold:1992" />the crystal morphology (habit), subject to the moisture conditions, can be subdivided into five groups (see diagram):
According to <bib id="Arnold:1992" /> the crystal morphology (habit) can be subdivided into five groups depending on the moisture condition present (see figure):


a) Multidirectional growth, large crystals with equilibrium shapes are formed on a wet surface, leaving the growing crystals immersed in the solution. The solution covers the whole surface or parts of it as a dense film.
a) Multidirectional growth, large crystals with equilibrium shapes are formed on a wet surface as long as the growing crystals are immersed in the solution. The solution covers the whole surface or parts of it as a dense film.


b) A granular crust of isometric crystals forms on a wet substrate, while the crystals are immersed in the solution film and are growing into multiple directions.  
b) A granular crust of isometric crystals forms on a wet substrate, while the crystals are immersed in the solution film and are growing into multiple directions.  


c) A fibrous crust forms on a medium moist substrate that is completely covered by the solution film. The columnar crystals grow from their base, and are still in contact with the nutrient solution, as they are uplifted.  
c) A fibrous crust forms on a medium moist substrate that is completely covered by the solution film. The columnar crystals grow from their base that is still in contact with the nutrient solution so that the dry crystals are moved upward.  


d) Columnar, thick whisker-like crystals grow on the humid surface and out of small pools of the solution.
d) Columnar, thick whisker-like crystals grow on the humid surface and out of small pools of the solution.


e) Very thin whiskers grow out of "solution dots" on the now nearly dry surface. The result is a fluffy salt efflorescence.
e) Very thin whiskers grow out of "solution drops" on the now nearly dry surface. The result is a fluffy salt efflorescence.


Salts can form their characteristic crystals under undisturbed crystallization conditions and sufficient supply of a nutrient salt solution. These crystals are called idiomorphic. Hypidiomorphic crystals only partially develop their own character, and xenomorphic crystallization means, that the crystal form is not related to the intrinsic shape.  
Salts can form their characteristic crystals under undisturbed crystallization conditions and when a sufficient supply of the salt solution is available. These crystals are called idiomorphic. Hypidiomorphic crystals are those that are only partially idiomorphic, while xenomorphic crystals refers to those whose shape does not resemble the intriinsic one.  
[[Image:Salzkristallisation Feuchteregime.jpg|thumb|center|600px|Relationship between crystal morphology and moisture regime (after <bib id="Arnold:1992"/>) ]]
[[Image:Salzkristallisation Feuchteregime.jpg|thumb|center|600px|Relationship between crystal morphology and moisture regime (after <bib id="Arnold:1992"/>) ]]


== Literature ==
== Literature ==
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[[Category:Schwarz,Hans-Jürgen]][[Category:R-CBlaeuer]] [[Category:saltdamage]][[Category:editing]][[Category:Decay_Pattern:Others]][[Category:Decay_Pattern:Ceramics]][[Category:Decay_Pattern:Glas]][[Category:Decay_Pattern:Pottery]][[Category:Decay_Pattern:Metal]][[Category:Decay_Pattern:Plaster]][[Category:Decay_Pattern:Natural_Stone]][[Category:Alveolarweathering]][[Category:Decay_Pattern:Organic_Materials]][[Category:Decay_Pattern:Wall_Paintings]]
[[Category:Schwarz,Hans-Jürgen]][[Category:R-CBlaeuer]] [[Category:saltdamage]][[Category:approved]][[Category:Decay_Pattern:Others]][[Category:Decay_Pattern:Ceramics]][[Category:Decay_Pattern:Glas]][[Category:Decay_Pattern:Pottery]][[Category:Decay_Pattern:Metal]][[Category:Decay_Pattern:Plaster]][[Category:Decay_Pattern:Natural_Stone]][[Category:Alveolarweathering]][[Category:Decay_Pattern:Organic_Materials]][[Category:Decay_Pattern:Wall_Paintings]]

Latest revision as of 10:15, 19 March 2023


Author: Hans-Jürgen Schwarz
English version by Sandra Leithäuser
back to SaltWiki:Portal

Introduction[edit]

Well documented and well analyzed deterioration patterns are of great importance for the assessment of new damage. This article provides an overview of deterioration patterns, that have been observed in the different material groups.

Material based collections of decay patterns are available for:

Glossary of Salt Efflorescences[edit]

Efflorescences are whitish, powdery or whisker-like crystals on the surface of porous materials. In most cases efflorescences are poorly cohesive and in general they are constituted by soluble salt crystals. On wall paintings, mortar, plaster, ceramic and natural stone, efflorescences repeatedly display certain typical forms. These are briefly characterized as follows:


Whiskers: a few microns thick to centimeters long, columnar, often curved crystals. Under specific conditions, crystals, which do not typically exhibit needle-building habits, grow as fine, hair-like shapes, the so-called whiskers. Whiskers have been observed developing from a variety of substances, e.g., metals, salts, etc. Their diameters range between 0.01 and 100 microns, while their length can reach up to a few centimeters. They grow preferentially in the longitudinal direction, while the growth on the lateral crystal plane is either suppressed or, to some extent, still in progress. Some whiskers accommodate a single, or a few, screw dislocations along their axis, causing a spiral growth at the tip, so that material along the lateral plane has to be transported to the tip. Some whiskers do not have screw dislocations, where the preferred growth takes place at the top- caused by a different mechanism. Finally, there are whiskers that do not grow at the top, but at their base, pushing the growing crystal upwards.

Whiskers are long, thin, sometimes curved crystals, here NaCl whiskers (from [Arnold.etal:1991]Title: Monitoring Wall Paintings Affected by soluble Salts
Author: Arnold, Andreas; Zehnder, Konrad
Link to Google Scholar
)



Feathery - Fluffy efflorescence: very loose, fluffy or cotton-like efflorescence, usually consisting of bent whiskers.

Efflorescence made of KNO3, the crystals are whiskers



Acicular crystals-bristly efflorescence: loose columnar whiskers, more or less perpendicular to the surface, 0.1 to several millimeters long, often only visible in raking light.

Salt crystals on a masonry joint; the individual crystals are whiskers



Powdery efflorescence: white, mealy, loose to dense or fluffy coating. Powdery efflorescence will develop differently depending on the type of salt crystallizing. Some salts, especially the less soluble ones such as gypsum, can bloom in this very fine form as soon as they crystallize. However, in the case of sodium sulfate this form of efflorescence results from the dehydration of the originally hydrated salt.

Powdery efflorescences of sodium sulfate



Salt pustules: separate, loose to compact salt crystals, to about 1 mm diameter.

Salt-induced pustules on a wall painting



Salt crust : crusts can be formed by soluble salts when they are highly concentrated developing salt aggregates with planar cohesion and very variable thicknesses (a few microns to mm)

Salt crust caused by de-icing salt



White loose crust (sugary crust): consists of individuals that are visible to the naked eye or low magnification as glass-clear crystals. Sugary crusts usually form in a moisture film. However, they can crystallize from a salt efflorescence that takes up water from the surrounding air, undergoing dissolution and followed by recrystallizing as the environment dries.

Halite crust on an exterior wall in Strahlsund



Satin crust: flat, shiny crust of salt. Thick, shiny crusts of gypsum are formed only by repeated recrystallization cycles over longer periods of time.

SEM photo of a satin like crust



Framboidal or botroidal crusts: crust of white, spherical aggregates- its surface resembles that of a raspberry or blackberry or even a cauliflower. Botroidal crusts occur preferentially along small defects (e.g., cracks) on an otherwise relatively dense plaster surface. They also can form as separate units on dense stones.

Framboidal efflorescences



Fibrous crust: crust composed of densely packed whiskers, perpendicular to the substrate. They usually develop on moist substrates.


Habit[edit]

  • The crystal habit describes the proportions and shape of crystals.


The habit of salts will change depending on the conditions during their formation.

Due to the crystal structure and the typical mineral and surface combinations, salts change in their physical appearance. On occasions, changes can also be caused by unilateral growth. We describe these mineral forms as follows:

  • isometric forms, if the development into all three spatial directions is approximately of the same size e.g.. all cubic crystals.
  • one-dimensional elongated forms: columnar, acicular, hair-like (whisker), fibrous, such as tourmaline, rutile, asbestos.
  • two-dimensional elongated forms: tabular, lamellar, foliated, scaly, micaceous, e.g.. barite and mica.
  • dendritic forms occur in the case of an incomplete crystal growth, developing plant-like shapes.


Formation of salt crystals, according to Arnold[edit]

According to [Arnold:1992]Title: Salze: Lästige weiße Ausblühungen oder Hauptschadensursache?
Author: Arnold, Andreas
Link to Google Scholar
the crystal morphology (habit) can be subdivided into five groups depending on the moisture condition present (see figure):

a) Multidirectional growth, large crystals with equilibrium shapes are formed on a wet surface as long as the growing crystals are immersed in the solution. The solution covers the whole surface or parts of it as a dense film.

b) A granular crust of isometric crystals forms on a wet substrate, while the crystals are immersed in the solution film and are growing into multiple directions.

c) A fibrous crust forms on a medium moist substrate that is completely covered by the solution film. The columnar crystals grow from their base that is still in contact with the nutrient solution so that the dry crystals are moved upward.

d) Columnar, thick whisker-like crystals grow on the humid surface and out of small pools of the solution.

e) Very thin whiskers grow out of "solution drops" on the now nearly dry surface. The result is a fluffy salt efflorescence.

Salts can form their characteristic crystals under undisturbed crystallization conditions and when a sufficient supply of the salt solution is available. These crystals are called idiomorphic. Hypidiomorphic crystals are those that are only partially idiomorphic, while xenomorphic crystals refers to those whose shape does not resemble the intriinsic one.

Relationship between crystal morphology and moisture regime (after [Arnold:1992]Title: Salze: Lästige weiße Ausblühungen oder Hauptschadensursache?
Author: Arnold, Andreas
Link to Google Scholar
)

Literature[edit]

[Arnold.etal:1991]Arnold, Andreas; Zehnder, Konrad (1991): Monitoring Wall Paintings Affected by soluble Salts. In: Cather, Sharon (eds.): The Conservation of Wall Paintings: Proceedings of a symposium organized by the Coutrauld Institut of Art and the Getty Conservation Institute, London, July 13-16, The Getty Conservation Institute, 103-136.Link to Google Scholar
[Arnold:1992]Arnold, Andreas (1992): Salze: Lästige weiße Ausblühungen oder Hauptschadensursache?. In: Jahresberichte Steinzerfall - Steinkonservierung, 2 (), 1-9Link to Google Scholar