Colour changes by laser irradiation of reddish building limestones
•This is the first time that XPS is used to determine the cause of colour change in coloured stones when cleaned with laser at 1064nm.•We demonstrate that the colour change in red limestones is due to a reduction in the state of oxidation of iron, in this case present as hematite.•XPS could be routi...
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Veröffentlicht in: | Applied surface science 2016-10, Vol.384, p.525-529 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | •This is the first time that XPS is used to determine the cause of colour change in coloured stones when cleaned with laser at 1064nm.•We demonstrate that the colour change in red limestones is due to a reduction in the state of oxidation of iron, in this case present as hematite.•XPS could be routinely used to analyse causes of colour changes during laser cleaning in other types of coloured building stones.
We have used X-ray photoelectron spectroscopy (XPS) as a novel method to investigate the causes of colour changes in a reddish limestone under irradiation by a Q-switched Nd:YAG 1064nm laser. We irradiated clean dry and wet surfaces of Pidramuelle Roja, a building stone frequently used in the Asturian heritage, at fluences ranging from 0.12 to 1.47Jcm−2. We measured the colour coordinates and undertook XPS analysis of the state of oxidation of iron both before and after irradiation. Visible colour changes and potential aesthetic damage occurred on dry surfaces from a fluence of 0.31Jcm−2, with the stone showing a greening effect and very intense darkening. The colour change on dry surfaces was considerably higher than on wet surfaces, which at the highest fluence (1.47Jcm−2) was also above the human visual detection threshold. The use of XPS demonstrated that the change in colour (chroma and hue) is associated with a reduction in the iron oxidation state on dry surfaces during laser irradiation. This points out to a potential routinary use of XPS to analyse causes of colour changes during laser cleaning in other types of coloured building stones. |
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ISSN: | 0169-4332 1873-5584 |
DOI: | 10.1016/j.apsusc.2016.05.031 |