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CONTOUR SCALING - SPALLING
CONTOUR SCALING - SPALLING

Sample

Sculpture of the upper floor of the main Altarpiece of Guarda Cathedral. Guarda. Portugal.

Oolitic white limestone with very refined grain polychromed wtih gold leaf.


Pathology Causes

Salt efflorescences and subflorescences (and fungal growths).

Visual Image

Author: Cetec-patrimoni
Description: In the centre of the sculpture (the chest and the abdomen) the pathology is a contour scaling and spalling that affects the surface of the stone. On the right side of the sculpture (the arm) flaking of gold leaf can be seen.

Image detail / macro

CONTOUR SCALING - SPALLING
Author: Cetec-patrimoni
Magnification: x45
Description: The salts present some pseudo-spherical dark grey particles with some granulate of light ochre as well as  efflorescences of soft aspect. They ussually contain some hyphas and various filaments.

Microscope Image

CONTOUR SCALING - SPALLING
Author: Cetec-patrimoni
Magnification:
Description: Detail of anhdric crystals with amoebic and bacillus shape and a gelatinous aspect on the surface. These crystal habits are caused by the exposure of hygroscopic salts to high humidity.

Associated Pathologies

Dust deposit.

Fungal growth.


Other Tests

X-ray spectrometry by SEM-EDS
XRD

Observations

The origin of the salts may be diverse, but the evidence of a lot of sodium carbonate is significant and reveals that they are released by the alcalis of cement. They could be related to the use of this kind of mortar in the former restorations of the building carried out in the roof and in the ceiling of the apse, whose dripping could have generated them.

Some other secondary mechanisms cannot be ignored such us the biodeterioration (mainly fungus) or the hydrolisis of feldspars and clay in the coat of the gilding preparation.


Bibliography

ICOMOS-ICS (2008). Illustrated glossary on stone deterioration pattern.

http://international.icomos.org/publications/monuments_and_sites/15/pdf/Monuments_and_Sites_15_ISCS_Glossary_Stone.pdf 

 

ORDAZ, J., & ESBERT, R. (1988). Glosario de términos relacionados con el deterioro de las piedras de construcción. Materiales de Construcción, 38 (209): 39-45. doi: 10.3989/mc.1988.v38.i209.847


Author

Manuel Iglesias Campos. manuel.iglesias@cetec-patrimoni.com

Restorer


Institution or Company

Universitat de Barcelona


Published Articles

IGLESIAS, M. et al. (2004). Pathologies of the Altarpiece from the main altar of the Sé da Guarda. Portugal. In Proceedings 6th International Symposium on the Conservation of Monuments in the Mediterranean Basin. Lisboa, 2004. pp. 153-158 (in CD).
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