Patricia Sanmartín

Bioreceptivity of building stones: a review.

In 1995, Guillitte defined bioreceptivity, a new term in ecology, as the ability of a material to be colonized by living organisms. Information about the bioreceptivity of stone is of great importance since it will help us to understand the material properties which influence the development of biological colonization in the built environment, and will also provide useful information as regards selecting stones for the conservation of heritage monuments and construction of new buildings. Studies of the bioreceptivity of stone materials are reviewed here with the aim of providing a clear set of conclusions on the topic. Definitions of bioreceptivity are given, stone bioreceptivity experiments are described, and finally the stone properties related to bioreceptivity are discussed. We suggest that a standardized laboratory protocol for evaluating stone bioreceptivity and definition of a stone bioreceptivity index are required to enable creation of a database on the primary bioreceptivity of stone materials.

Relationship between color and pigment production in two stone biofilm-forming cyanobacteria (Nostoc sp. PCC 9104 and Nostoc sp. PCC 9025)

Previous studies have provided evidence that color measurements enable on site quantification of superficial biofilms, thereby avoiding the need for sampling. In the present study, the efficiency of color measurements to evaluate to what extent pigment production is affected by environmental parameters such as light intensity, combined nitrogen and nutrient availability, was tested with two cyanobacteria, Nostoc sp. strains PCC 9104 and PCC 9025, which form biofilms on stone. Both strains were acclimated, in aerated batch cultures for 2 weeks, to three different culture media: BG-11, BG-110, and BG-110/10 at either high or low light intensity. The content of chlorophyll a, carotenoids, and phycocyanins was measured throughout the experiment, together with variations in the color of the cyanobacteria, which were represented in the CIELAB color space. The results confirmed that the CIELAB color parameters are correlated with pigment content in such a way that variations in the latter are reflected as variations in color.

New Nanomaterials for Protecting and Consolidating Stone

The sol-gel process has been found to be successful in applications for the conservation and restoration of stone. However, a well-known drawback of the materials obtained by this process is their tendency to crack during drying inside the pores of the treated stone. In this article, we present an overview of our current research centred on producing crack-free sol-gel materials for consolidating and protecting building stone. A novel synthesis, in which a surfactant acts as a template to make the pore size of the gel network coarser and more uniform, is shown to provide an effective alternative for preventing the cracking of consolidants. We also highlight an alternative pathway, in which we add an organic component to the silica precursor in the presence of the surfactant. The hybrid organic-inorganic gel prepared in our laboratory provides excellent waterproofing to the stones under study.

Spectrophotometric color measurement for early detection and monitoring of greening on granite buildings

This paper addresses the detection and monitoring of the development of epilithic phototrophic biofilms on the granite façade 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 Δb*: +0.59 CIELAB units that correspond, in the present study, to 6.3 μg of biomass dry weight cm−2 and (8.43 ± 0.24) × 10−3 μg of extracted chlorophyll a cm−2.

Effect of Surface Finish on Roughness, Color, and Gloss of Ornamental Granites

The effects of four of the most common types of surface finish on the appearance of five varieties of ornamental granite, all widely used in building construction and selected for their different colors, were analyzed by means of roughness, color, and gloss measurements. The results demonstrated that different surface finishes produce differences in color, especially in the lightness parameter (L* ), and that the magnitude of these differences depends on the color of the ornamental granite and is greatest in dark colored rocks. However, the variation in the color parameters with the different surface finishes did not depend on roughness, and no general conclusions could be drawn regarding the influence of the roughness on the color of ornamental granite. Gloss values were affected by the color of the ornamental granite, but in a different way for smooth and rough surfaces. Variation in gloss also depended on the mineral composition of the rock. Gloss and roughness were inversely related, but only within t...

Color of cyanobacteria: some methodological aspects

Although the color of cyanobacteria is a very informative characteristic, no standardized protocol has, so far, been established for defining the color in an objective way, and, therefore, direct comparison of experimental results obtained by different research groups is not possible. In the present study, we used colorimetric measurements and conventional statistical tools to determine the effects on the measurement of the color of cyanobacteria, of the concentration of the microorganisms and their moisture content, as well as of the size of the target area and the minimum number of measurements. It was concluded that the color measurement is affected by every factor studied, but that this can be controlled for by making at least 10 consecutive measurements/9.62 cm(2) at different randomly selected points on the surface of filters completely covered by films of cyanobacteria in which the moisture contents are higher than 50%.

Melding the Old with the New: Trends in Methods Used to Identify, Monitor, and Control Microorganisms on Cultural Heritage Materials

Microbial activity has an important impact on the maintenance of cultural heritage materials, owing to the key role of microorganisms in many deterioration processes. In order to minimize such deleterious effects, there is a need to fine-tune methods that detect and characterize microorganisms. Trends in microbiology indicate that this need can be met by incorporating modern techniques. All of the methods considered in this review paper are employed in the identification, surveillance, and control of microorganisms, and they have two points in common: They are currently used in microbial ecology (only literature from 2009 to 2015 is included), and they are often applied in the cultural heritage sector. More than 75 peer-reviewed journal articles addressing three different approaches were considered: molecular, sensory and morphological, and biocontrol methods. The goal of this review is to highlight the usefulness of the traditional as well as the modern methods. The general theme in the literature cited suggests using an integrated approach.

Antimicrobial Properties of Nanomaterials Used to Control Microbial Colonization of Stone Substrata

Nanoparticle-based materials are applied in the conservation of cultural heritage for their consolidating and self-cleaning abilities. Recently, nanoparticles (NPs) have been found to possess inherent antimicrobial activity, which has stimulated their application in the control of microbial colonization of stone and other mineral materials. A literature survey shows diverse testing procedures and limited research on the antimicrobial effectiveness of nanomaterials under real conditions. Most research reports laboratory-scale studies, employing either mono- or dual species (two organisms) assays over short-term incubation of days or weeks. Antimicrobial effectiveness is often assessed using microbiological, microscopy-based methods and surface colorimetry. There is a potential adverse ecotoxicological impact of NPs after release from treated surfaces. This chapter covers the antimicrobial properties of NPs and their limitations and advantages for application on built cultural heritage.