Papers by Daniel Vázquez-Nion
Compost Science & Utilization, 2015
Measurement, 2014
ABSTRACT In this study, a digital CMOS camera was calibrated for use as a non-contact colorimeter... more ABSTRACT In this study, a digital CMOS camera was calibrated for use as a non-contact colorimeter for measuring the color of granite artworks. The low chroma values of the granite, which yield similar stimulation of the three color channels of the camera, proved to be the most challenging aspect of the task. The appropriate parameters for converting the device-dependent RGB color space into a device-independent color space were established. For this purpose, the color of a large number of Munsell samples (corresponding to the previously defined color gamut of granite) was measured with a digital camera and with a spectrophotometer (reference instrument). The color data were then compared using the CIELAB color formulae. The best correlations between measurements were obtained when the camera works to 10-bits and the spectrophotometric measures in SCI mode. Finally, the calibrated instrument was used successfully to measure the color of six commercial varieties of Spanish granite.
International Biodeterioration & Biodegradation, 2014
In Galicia (northwest Spain), the mild humid climate causes the walls of many buildings to be per... more In Galicia (northwest Spain), the mild humid climate causes the walls of many buildings to be permanently damp, which leads to the appearance of phototrophic colonization ("greening") on the walls. Prolonged, deeply penetrating damp can be halted by the application of plastic-based products. Ventilated facades are separated from the structural wall, which enables the protective products to be applied to the back of the facade. This is an important advantage since it allows the use of coloured paints, which would be unacceptable for use on the exterior face of a building, and other plastic-based compounds that are degraded by solar radiation. The main aim of this laboratory-based study was to evaluate the usefulness of several plastic-based products (viz. white plastic paint, Sikaflex Ò , Tegosivin Ò , and Tegovakon Ò ) for inhibiting biological colonization on the exterior faces of buildings when applied to the back of the stone cladding. The results of the study demonstrated an unexpected effect: the application of plasticbased products to the back of specimens simulating ventilated granite facades does not inhibit biological colonization, but increases the tertiary bioreceptivity of granitic rocks.
International Biodeterioration & Biodegradation, 2013
Pigment content provides valuable information about the growth and physiological status of organi... more Pigment content provides valuable information about the growth and physiological status of organisms. This study investigated the relationship between pigment content (chlorophyll a, total carotenoids and phycobiliproteins) and reflectance color measurements, expressed by means of the CIELAB color coordinates. The experimental design was carried out with a biofilm-forming cyanobacterium of the genus Nostoc grown under different environmental conditions (nitrate and phosphate concentrations and light intensity). Analysis of the results revealed a close correlation between pigment content and CIELAB color coordinates and enabled formulation of predictive equations for estimating chlorophyll a and total carotenoid content. The interest in monitoring biofilm development on cultural heritage monuments has arisen within the field of preventive conservation and explains the importance of developing a simple non-destructive method of microorganism assessment based on color measurements, which can be performed rapidly on site and is cost-effective.
Biofouling, 2012
This paper addresses the detection and monitoring of the development of epilithic phototrophic bi... more This paper addresses the detection and monitoring of the development of epilithic phototrophic biofilms on the granite fac¸ade of an institutional building in Santiago de Compostela (NW Spain), and reports a case study of preventive conservation. The results provide a basis for establishing criteria for the early detection of phototrophic colonization (greening) and for monitoring its development on granite buildings by the use of color changes recorded with a portable spectrophotometer and represented in the CIELAB color space. The results show that parameter b* (associated with changes of yellowness-blueness) provides the earliest indication of colonization and varies most over time, so that it is most important in determining the total color change. The limit of perception of the greening on a granite surface was also established in a psycho-physical experiment, as Db*: þ0.59 CIELAB units that correspond, in the present study, to 6.3 mg of biomass dry weight cm 72 and (8.43 + 0.24) 6 10 73 mg of extracted chlorophyll a cm 72 .
Environmental Microbiology, 2014
This study addresses the primary and secondary bioreceptivity of schist used as a support for pre... more This study addresses the primary and secondary bioreceptivity of schist used as a support for prehistoric rock art in the Côa Valley Archaeological Park (north-east Portugal) and provides some parameters that can be related to the risk of biologically induced schist weathering. Samples of freshly quarried and naturally weathered schist were characterized in terms of their intrinsic properties and maintained in controlled environmental conditions after inoculation with biofilm-forming cyanobacteria. The physical properties of the studied schist, as well as its abrasion pH, all varied according to the weathering degree of the samples and so did its susceptibility to colonization by biofilm-forming cyanobacteria. Complete separation between weathered and unweathered schist samples in terms of laboratory-induced photosynthetic biomass was obtained by measuring total colour change in the CIE (International Commission on Illumination) L*a*b* colour space. Weathered schist was more bioreceptive than unweathered schist, associated with increased open porosity, water saturation, capillary water and capillarity coefficient and decreased abrasion pH. In the future, it might be possible to determine the susceptibility of schist surfaces to biological colonization through evaluation of colour differences associated with the different weathering degrees presented by those surfaces prior to colonization.
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Papers by Daniel Vázquez-Nion