Deterioration Patterns Wallpaintings: Difference between revisions

From Saltwiki
Jump to navigation Jump to search
Line 18: Line 18:
[[file:Blumenkohlkruste Nehren NWW Detail.jpg|thumb|300px|left|Framboidal efflorescence, grave chamber Nehren]]
[[file:Blumenkohlkruste Nehren NWW Detail.jpg|thumb|300px|left|Framboidal efflorescence, grave chamber Nehren]]
[[file:Blumenkohlkruste Nehren NWW.jpg|thumb|300px|right|Framboial efflorescence, grave chamber Nehren]]
[[file:Blumenkohlkruste Nehren NWW.jpg|thumb|300px|right|Framboial efflorescence, grave chamber Nehren]]
The formation of firmly adhering framboidal efflorescence is characteristic for some conditions. The composition may consist of calcium carbonate or gypsum,calcium sulfate dihydrate. Depending on the contaminants present, the efflorescence nay appear whitish, yellowish, reddish or brownish. Biogenic precipitate can be stored within the crust deposits.
The formation of firmly adhering framboidal efflorescence is characteristic for some conditions. The composition may consist of calcium carbonate or gypsum,calcium sulfate dihydrate. Depending on the contaminants present, the efflorescence may appear whitish, yellowish, reddish or brownish. Biogenic precipitate can be stored within the crust deposits.
<br clear=all>
<br clear=all>



Revision as of 17:29, 7 January 2013

Author: Nicole Riedl

English Translation by Hans-Jürgen Schwarz andSandra Leithäuser

back to Decay Pattern


Examples of damage by salt progression[edit]

Calcareous concretions (sinter crusts)[edit]

Calcareous concretion, Roman wall-painting, grave chamber, Nehren
Calcareous concretion, Roman wall-painting, grave chamber Nehren

Precipitation of calcium carbonate on the surface of wall paintings begins by a fine white veil and may continue to form a white, dense calcareous concretion. It is characterized by a high stability and strong bond with the painting. The vapor permeability of the wall painting is reduced and the layered crust deposits affects the aesthetic appearance considerably.

Framboidal efflorescence (cauliflower crust)[edit]

Framboidal efflorescence, grave chamber Nehren
Framboial efflorescence, grave chamber Nehren

The formation of firmly adhering framboidal efflorescence is characteristic for some conditions. The composition may consist of calcium carbonate or gypsum,calcium sulfate dihydrate. Depending on the contaminants present, the efflorescence may appear whitish, yellowish, reddish or brownish. Biogenic precipitate can be stored within the crust deposits.

Hygroscopic salts[edit]

Gypsum crust and hygroscopic salts, grave chamber Nehren
Gypsum crust and hygroscopic salts, grave chamber Nehren

The photograph shows darkened areas along fissures in the paint layer and topcoat of the plaster that also has crust deposits on it. The reason for this is the presence of hygroscopic salts that tend to bind moisture originating from the plaster or from the ambient air. The moisture film will reflect light more giving the surface its darker appearance.

Powdery salt deposits[edit]

Powdery salt efflorescence, sodium sulfate, grave chamber Nehren
Powdery salt efflorescence, sodium sulfate, grave chamber Nehren

White, loosely adhering salt efflorescence on the plaster and the paint surface. It is characterized by small crystalline, soft, powdery efflorescence which may be formed by several different salts. The example shows sodium sulfate deposits on a repair plaster made with trass cement.

Scaling due to salt crystallization[edit]

Scaling, grave chamber Nehren
Scaling, grave chamber Nehren

The crystallizing salts can detach the painting layer or even the topcoat of the plaster. This occurs as a result of the phase transition from salt solution to salt crystals that entails an expansion so that depending on where the salts crystallize a thinner or a thicker layer may be detached.