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<!-- The English version of this text was edited by Sandra Leithäuser-->
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Author: [[user:Hschwarz|Hans-Jürgen Schwarz]]
Author: [[user:Hschwarz|Hans-Jürgen Schwarz]]
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English version by [[user:SLeithaeuser|Sandra Leithäuser]]
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back to [[Measures]] <br>  
back to [[Measures]] <br>  
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== Abstract  ==
== Abstract  ==
Damaging salts can be transformed into less damaging compounds using chemical salt conversion. One method converts soluble salts into poorly soluble or insoluble compounds, resulting in the salts being less damaging. Another method transforms insoluble salts into more soluble ones in order to remove them more easily.
Damaging soluble salts can be transformed into less damaging ones by their conversion into insoluble salts. Two methods can be used. The first one converts soluble salts into poorly soluble or insoluble compounds, thus diminishing the number and degree of crystallization cycles. The second one transforms the less soluble salts into far more soluble ones in order to remove them more easily.


== [[Removal of salts by salt conversion]]  ==
== [[Removal of salts by salt conversion]]  ==


Conservation practice uses various methods for the removal of soluble salts and salt crusts. Often acids such as hydrochloric acid or acetic acid were used to remove calcium carbonate crusts, but this can lead to subsequent damages if procedures are not followed diligently.<bib id="Hammer:1996" />  The use of hexafluorosilicic acid has been documented, too. The forentine method <bib id=Matteini:1991/> of "gypsum transformation" also includes the dissolution of the gypsum crust with ammonium carbonate. Ion exchangers have been in use for many years to remove crusts.<bib id="Pursche:2001" />
Conservation practice uses various methods for the removal of soluble salts and salt crusts. In the past, acids such as hydrochloric or acetic acid were often used to remove calcium carbonate crusts. However, this can lead to subsequent damages if the correct procedure is not followed diligently.<bib id="Hammer:1996" />  The use of hexafluorosilicic acid has also been documented. The Florentine method <bib id="Matteini:1991"/> of "gypsum transformation" is based on the dissolution of the gypsum crust with ammonium carbonate. Ion exchangers have also been in use for many years to remove crusts.<bib id="Pursche:2001" />


== [[Immobilization of salts]]  ==
== [[Immobilization of salts]]  ==


Immobilization is the conversion of readily soluble salts into poorly soluble or insoluble salts and thus relatively harmless compounds. This appears to be simple and obvious but problems arise in the practical application. Masonry not only incorporates defined salts, such as calcium nitrate or magnesium sulfate, but also relatively complex mixtures, which may be partly crystalline, partly present as a salt solution. The most common compounds are carbonates, nitrates, chlorides and sulphates, the most common cations are sodium, potassium, magnesium and calcium. It should be noted, that nitrate compounds can not be converted into insoluble salts, as there are no poorly soluble or insoluble nitrate compounds. This leaves chlorides, sulfates and some limited options for carbonates as the only possibilities for immobilization treatment.  
Immobilization is the conversion of readily soluble salts into poorly soluble or insoluble salts that are therefore less deteriorating compounds. This appears to be simple but the problem is that not all ions form highly insoluble compounds, for example, there are no poorly soluble or insoluble nitrate compounds. Furthermore, masonry usually contains a mixture of ions, not only specific salts, such as calcium nitrate or magnesium sulfate. Thus, even when some salts crystallize out, a solution containing these and other ions will also be present. The most common anions are carbonates, nitrates, chlorides and sulfates, the most common cations are sodium, potassium, magnesium and calcium. This leaves chlorides, sulfates and some limited options for carbonates as the only possibilities for an immobilization treatment.  


Today, barium solutions are employed most frequently, but formerly lead hexafluorosilicate was often used.
Currently, barium solutions, such as barium hydroxide, are the most frequently employed to immobilize sulfates. In the past, lead hexafluorosilicate was used to immobilize chlorides as well as carbonates, however the fluorosilicate will react with any calcium carbonate in the substrate by turning it into calcium fluoride, and can attack silicate minerals as during the reaction hydroflouric acid is released.  


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== Literature ==
== Literature ==


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<biblist />  


[[Category:Measures]][[Category:Salt Conversion]] [[Category:Hschwarz]] [[Category:R-SLaue]] [[Category:inProgress]]
[[Category:Measures]][[Category:Salt Conversion]] [[Category:Schwarz,Hans-Jürgen]] [[Category:R-SLaue]] [[Category: approved]]

Latest revision as of 10:44, 20 September 2013

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

Abstract

Damaging soluble salts can be transformed into less damaging ones by their conversion into insoluble salts. Two methods can be used. The first one converts soluble salts into poorly soluble or insoluble compounds, thus diminishing the number and degree of crystallization cycles. The second one transforms the less soluble salts into far more soluble ones in order to remove them more easily.

Removal of salts by salt conversion

Conservation practice uses various methods for the removal of soluble salts and salt crusts. In the past, acids such as hydrochloric or acetic acid were often used to remove calcium carbonate crusts. However, this can lead to subsequent damages if the correct procedure is not followed diligently.[Hammer:1996]Title: Salze und Salzbehandlung in der Konservierung von Wandmalerei und Architekturoberfläche.
Author: Hammer, Ivo
Link to Google Scholar
The use of hexafluorosilicic acid has also been documented. The Florentine method [Matteini:1991]Title: In Review: An Assessmant of Florentine Methods of Wall Painting Conservation Based on the Use of Mineral Treatments
Author: Matteini, Mauro
Link to Google Scholar
of "gypsum transformation" is based on the dissolution of the gypsum crust with ammonium carbonate. Ion exchangers have also been in use for many years to remove crusts.[Pursche:2001]Title: Konservierung von Wandmalerei, Reaktive Behandlungsmethoden zur Bestandserhaltung
Link to Google Scholar

Immobilization of salts

Immobilization is the conversion of readily soluble salts into poorly soluble or insoluble salts that are therefore less deteriorating compounds. This appears to be simple but the problem is that not all ions form highly insoluble compounds, for example, there are no poorly soluble or insoluble nitrate compounds. Furthermore, masonry usually contains a mixture of ions, not only specific salts, such as calcium nitrate or magnesium sulfate. Thus, even when some salts crystallize out, a solution containing these and other ions will also be present. The most common anions are carbonates, nitrates, chlorides and sulfates, the most common cations are sodium, potassium, magnesium and calcium. This leaves chlorides, sulfates and some limited options for carbonates as the only possibilities for an immobilization treatment.

Currently, barium solutions, such as barium hydroxide, are the most frequently employed to immobilize sulfates. In the past, lead hexafluorosilicate was used to immobilize chlorides as well as carbonates, however the fluorosilicate will react with any calcium carbonate in the substrate by turning it into calcium fluoride, and can attack silicate minerals as during the reaction hydroflouric acid is released.


Literature

[Hammer:1996]Hammer, Ivo (1996): Salze und Salzbehandlung in der Konservierung von Wandmalerei und Architekturoberfläche.. In: Pursche, Jürgen (eds.): Salzschäden an Wandmalereien, Bayerisches Landesamt für Denkmalpflege, 81-106.Link to Google Scholar
[Matteini:1991]Matteini, Mauro (1991): In Review: An Assessmant of Florentine Methods of Wall Painting Conservation Based on the Use of Mineral Treatments. 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, 1987, The Getty Conservation Institute, 137-148.Link to Google Scholar
[Pursche:2001]Pursche, Jürgen (eds.) (2001): Konservierung von Wandmalerei, Reaktive Behandlungsmethoden zur Bestandserhaltung, Bayerisches Landesamt für Denkmalpflege, MünchenLink to Google Scholar