¿Qué tan no tóxico es el grabado no tóxico?

The world of printmaking changed in the 1990s with a series of rediscoveries that started with electrolytic etching, followed by the applications of mordents. These methodologies have relegated the use of nitric acid from the printmaking workshop, together with other potentially toxic substances, that include colophony resin, asphalt and petroleum-derived solvents. the dream of the modern printmaker is a technique that is safe and free of any toxic substances; however, as always, in any place, there are risks for our health, and having avoided toxic substances from the etching, it could be argued that electrolysis also produces dangerous gases. Then, the question arises: How safe is electrolytic etching? In this context, the main fear is the hydrogen gas liberated during electrolytic etching when table salt is used as a universal electrolyte. This gas is highly flammable. Nevertheless, its associated risk depends on its concentration in an enclosed environment, such as a workshop. For this reason, the aim of this paper was quantification of the amount of hydrogen generated during 15 minutes period of electrolysis, using aluminum plates of 5x8 cm, this metal was selected for the experiments because is the most reactive from the other metals used in printmaking. The average amount of hydrogen produced in 12 experiments was 120ml. Under the experimental conditions evaluated, to get a hazardous concentration of hydrogen in a hermetically sealed enclosure, of 4x4x4 meters, it would be necessary to etch out one kilogram of aluminum, equivalent to 84 etchings in plates of 240x150x1,6mm, whose average weight decreased 12g after the process. Fortunately, the accumulation of hydrogen in a standard workshop can be easily avoided with an open window or better with two open opposing windows. In conclusion the electrolytic etching using table salt is a safe method to etching aluminum and any other metal, such as copper, iron, zinc, and steel.El mundo del grabado cambió en los años noventa con una serie de redescubrimientos, que comenzaron con el grabado electrolítico, seguido por las aplicaciones de los mordentes salinos. Esas metodologías han relegado el uso del ácido nítrico del taller de grabado, junto con otra sustancia potencialmente tóxica, que incluye resina de colofonia, asfalto y muchos solventes del petróleo. El sueño del grabador moderno es una técnica segura y libre de cualquier sustancia tóxica. Sin embargo, siempre, en cualquier lugar hay riesgos para nuestra salud y habiendo evitado las sustancias tóxicas en el grabado, se podría argumentar que la electrólisis también produce gases peligrosos. Entonces, surge la pregunta: ¿Qué tan seguro es el grabado electrolítico? En este contexto, el principal temor es el hidrógeno liberado durante el grabado electrolítico cuando se utiliza sal de mesa como un electrolito universal. Este gas es altamente inflamable, sin embargo, su riesgo asociado depende de su concentración en un entorno cerrado, tal como un taller. Por este motivo, el objetivo de este trabajo fue la cuantificación de la cantidad de hidrógeno generado durante 15 minutos de electrólisis, utilizando placas de aluminio de 5x8 cm, este metal fue seleccionado para los experimentos porque es el más reactivo de entre los otros metales utilizados en grabado. La cantidad media de hidrógeno producida en 12 experimentos fue de 120 ml. Bajo las condiciones experimentales evaluadas, para obtener una concentración peligrosa de hidrógeno en un recinto herméticamente cerrado, de 4x4x4 metros, sería necesario consumir un kilogramo de aluminio, equivalente a 84 grabados en láminas de 240x150x1,6mm, cuyo peso promedio disminuyera 12g después del proceso. Afortunadamente, la acumulación de hidrógeno en todo caso se puede evitar fácilmente con una ventana abierta o, mejor aún con dos ventanas en lados opuestos del taller. En conclusión, el grabado electrolítico usando sal de mesa es un método seguro para grabar aluminio y cualquier otro metal, como cobre, hierro, zinc y acero

Photonic Crystal Characterization of the Cuticles of Chrysina chrysargyrea and Chrysina optima Jewel Scarab Beetles

A unified description involving structural morphology and composition, dispersion of optical constants, modeled and measured reflection spectra and photonic crystal characterization is devised. Light reflection spectra by the cuticles of scarab beetles (Chrysina chrysargyrea and Chrysina optima), measured in the wavelength range 300–1000 nm, show spectrally structured broad bands. Scanning electron microscopy analysis shows that the pitches of the twisted structures responsible for the left-handed circularly polarized reflected light change monotonically with depth through the cuticles, making it possible to obtain the explicit depth-dependence for each cuticle arrangement considered. This variation is a key aspect, and it will be introduced in the context of Berreman’s formalism, which allows us to evaluate reflection spectra whose main features coincide in those displayed in measurements. Through the dispersion relation obtained from the Helmholtz’s equation satisfied by the circular components of the propagating fields, the presence of a photonic band gap is established for each case considered. These band gaps depend on depth through the cuticle, and their spectral positions change with depth. This explains the presence of broad bands in the reflection spectra, and their spectral features correlate with details in the variation of the pitch with depth. The twisted structures consist of chitin nanofibrils whose optical anisotropy is not large enough so as to be approached from modeling the measured reflection spectra. The presence of a high birefringence substance embedded in the chitin matrix is required. In this sense, the presence of uric acid crystallites through the cuticle is strongly suggested by frustrated attenuated total reflection and Raman spectroscopy analysis. The complete optical modeling is performed incorporating the wavelength-dependent optical constants of chitin and uric acid

Pristine but metal-rich Río Sucio (Dirty River) is dominated by Gallionella and other iron-sulfur oxidizing microbes

Whether the extreme conditions of acidity and heavy metal pollution of streams and rivers originating in pyritic formations are caused primarily by mining activities or by natural activities of metal-oxidizing microbes living within the geological formations is a subject of considerable controversy. Most microbiological studies of such waters have so far focused on acid mine drainage sites, which are heavily human-impacted environments, so it has been problematic to eliminate the human factor in the question of the origin of the key metal compounds. We have studied the physico-chemistry and microbiology of the Río Sucio in the Braulio Carrillo National Park of Costa Rica, 22 km from its volcanic rock origin. Neither the remote origin, nor the length of the river to the sampling site, have experienced human activity and are thus pristine. The river water had a characteristic brownish-yellow color due to high iron-dominated minerals, was slightly acidic, and rich in chemolithoautotrophic iron- and sulfur-oxidizing bacteria, dominated by Gallionella spp. Río Sucio is thus a natural acid-rock drainage system whose metal-containing components are derived primarily from microbial activities.Universidad de Costa Rica/[809-B4-282]/UCR/Costa RicaEuropean Commission-Science and Technology Development for in situ detection and characterization of subsurface life on the Iberian Pyritic Belt/[ERC250350-IPBSL]/ERC IPBSL/Unión EuropeaUSA National Science Foundation/[0959894]//Estados UnidosConsejo Superior de Investigaciones Científicas//CSIC/EspañaEuropean Union FP7 programme /[607346]/EU/UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigaciones en Productos Naturales (CIPRONA)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de QuímicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Biología Celular y Molecular (CIBCM