Calcium Oxalate on Limestone Surface of Heritage Buildings

Ion, Rodica Mariana; Teodorescu, Sofia; Ştirbescu, Raluca Maria; Bucurică, Ioan Alin; Dulamă, Ioana Daniela; Ion, Mihaela Lucia

doi:10.4028/www.scientific.net/kem.750.129

Cited by 4 publications

(4 citation statements)

References 14 publications

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“…Calcium oxalate is itself colorless but when organic compounds, mainly derived from the metabolic activity of lichens, fungi and bacteria (from oxalic acid which reacts with calcite to form a thin calcium oxalate lm) and other mineral grains (such as quartz, feldspar) are present, the patina may acquire a yellowish-brown hue (Ion et al 2017). Thus, the color on this balustrade could possibly originate from calcium oxalate mixed with other mineral grains such as soil dust.…”

Section: Balustrade From Batalha Monastery Royal Cloistermentioning

confidence: 99%

Orange Layered Patinas on Limestone Surface in the Batalha Monastery (Portugal): Characterization and Decay Patterns

Ding¹,

Redol²,

Angelini³

et al. 2021

Preprint

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Samples of orange patinas found on a limestone balustrade and an ornament of the Batalha Monastery have been investigated by X-ray micro-diffractometry (µ-XRD) and Low-Vacuum Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry (LV-SEM + EDS). Aim of the study was to determine the composition of the layered patinas, assess whether they were been intentionally applied or naturally formed, and study their degradation patterns. Preliminary results revealed that the orange patinas on the balustrade and the ornament showed different compositions and appearance, suggesting distinct formation pathways. Orange layers on the ornament which suffers salt decay and delamination nowadays, mainly consisted of gypsum with hematite as a minor component, implying the possibility of an intentional application of a mixture of ochre and lime as tint plaster. Orange patinas on the balustrade show the presence of Ca-oxalates, abundant weddellite and minor whewellite, with minor hematite suggesting the yellowish/orange color to be due to Ca-oxalate patinas imbedding soil dust airborne particles. Such patina was possibly formed naturally either by the chemical attack due to atmospheric air pollutants from traffic exhausts emissions or by bacterial activity. No delamination was observed, abrasion is the major decay phenomenon on the balustrade sample. A comparison was made between this patina and the so called “scialbatura”, a surface yellowish coating often found by conservators on limestone and marble in ancient monuments in the Mediterranean region.

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Section: Balustrade From Batalha Monastery Royal Cloistermentioning

confidence: 99%

Orange Layered Patinas on Limestone Surface in the Batalha Monastery (Portugal): Characterization and Decay Patterns

Ding¹,

Redol²,

Angelini³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…Calcium oxalate is itself colorless, but when organic compounds, mainly derived from the metabolic activity of lichens, fungi, and bacteria (from oxalic acid which reacts with calcite to form a thin calcium oxalate film) and other mineral grains (such as quartz and feldspar) are present, the patina may acquire a yellowish-brown hue (Ion et al 2017). Thus, the color on this window tracery could possibly originate from calcium oxalate mixed with other mineral grains such as soil dust.…”

Section: Window Tracery From Batalha Monastery Royal Cloistermentioning

confidence: 99%

Surface orange patinas on the limestone of the Batalha Monastery (Portugal): characterization and decay patterns

Ding

Redol

Angelini

et al. 2021

Environ Sci Pollut Res

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Samples of orange patinas found on a limestone window tracery and an ornament of the Batalha Monastery have been investigated by X-ray micro-diffractometry (μ-XRD) and low-vacuum scanning electron microscopy coupled with energy dispersive spectrometry (LV-SEM + EDS). The aim of the study was to determine the composition of the layered patinas, assess whether they have been intentionally applied or naturally formed, and study their degradation patterns. Preliminary results revealed that the orange patinas on the window tracery and the ornament showed different compositions and appearance, suggesting distinct formation pathways. Orange patinas on the ornament, which are now showing decay and delamination patterns, mainly consisted of gypsum with hematite as a minor component, implying the possibility of an intentional application of a mixture of ochre and lime as tint plaster. Orange patinas on the window tracery show, instead, the presence of Ca-oxalates, abundant weddellite, and minor whewellite, with minor hematite suggesting the yellowish/orange color as being due to Ca-oxalate patinas imbedding soil dust airborne particles. Such patina was possibly formed naturally either by the chemical attack due to atmospheric air pollutants from traffic exhausts emissions or by bacterial activity. No delamination was observed on the window tracery sample with granular decohesion as the major decay phenomenon. A comparison was made between this patina and the so-called scialbatura, a surface yellowish coating often found by conservators on limestone and marble in ancient monuments in the Mediterranean region.

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“…In order to preponderate these drawbacks, we designed a modified TEOS based consolidant nanocomposite; calcium oxalate (CaOx) has been integrated into silica matrix, in order to achieve chemical affinity with the carbonaceous nature of limestones. It is well-known that calcium oxalate has played a crucial, protective role in monuments, since quantity of it has been detected in the patina, present on historical surfaces that have been maintained in fairly good conditions [5,6].…”

Section: Introductionmentioning

confidence: 99%

TEOS-PDMS-Calcium Oxalate Hydrophobic Nanocomposite for Protection and Stone Consolidation

Maravelaki-Kalaitzaki

Kapetanaki

Stefanakis

2021

Heritage

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A treatment for both protection and consolidation, was synthesized in a simplified procedure through the sol gel process. Synthesized nano-calcium oxalate (CaOx) was incorporated into tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS), providing a hybrid hydrophobic consolidant nanocomposite. Oxalic acid was selected due to its ability to catalyse the hydrolysis of TEOS, as a drying control agent, but also because of its contribution at the formation of the calcium oxalate in reaction with calcium hydroxide. CaOx, incorporated into the silica matrix of the final copolymer, exhibits interfacial compatibility with the stone substrate and simultaneously strengthens the treated surface, since CaOx appears to be more stable than calcium carbonate. The hydrolysis of TEOS, as well as the formation of CaOx was evaluated through thermogravimetric analysis (TG/DTA). The nanocomposite consists of particles with approximately 7–700 nm in size range, as shown in TEM images. The consolidation, in combination with the hydrophobicity of surface resulted in an increase of the resistance to decay. Mechanical properties were enhanced as evaluated by ultrasonic pulse velocity on treated and untreated surfaces. Furthermore, water contact angle, as well as water absorption by capillarity test, showed improved water repellency of treated stones. Finally, this treatment doesn’t alter the aesthetic surface parameters, a fact that is essential in cultural heritage conservation, while the consolidant remains intact under UV and moisture exposure.

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Calcium Oxalate on Limestone Surface of Heritage Buildings

Cited by 4 publications

References 14 publications

Orange Layered Patinas on Limestone Surface in the Batalha Monastery (Portugal): Characterization and Decay Patterns

Orange Layered Patinas on Limestone Surface in the Batalha Monastery (Portugal): Characterization and Decay Patterns

Surface orange patinas on the limestone of the Batalha Monastery (Portugal): characterization and decay patterns

TEOS-PDMS-Calcium Oxalate Hydrophobic Nanocomposite for Protection and Stone Consolidation

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