From paradox to principles: where next for scientific advice to governments?

Scientific advice to governments has never been in greater demand; nor has it been more contested. From climate change to cyber-security, poverty to pandemics, food technologies to fracking, the questions being asked of scientists, engineers and other experts by policymakers, the media and the wider public continue to multiply and increase in complexity. At the same time, the authority and legitimacy of experts are under increasing scrutiny. This thematic article collection (‘special issue’) brings together perspectives on the theory, practice and politics of scientific advice that build on the conclusions of the landmark conference in Auckland in August 2014, which led to the creation of the International Network for Government Science Advice (INGSA). We hope that new papers will continue to be added to this collection over the next year and beyond, making it a living, fully open access repository for new scholarship and policy thinking—and an important contribution to the emerging science and art of scientific advice

Modelization of the optical and colorimetric properties of lustred ceramics

International audienceThe lustre decoration is one of the most famous decorations of glazed ceramics in the Mediterranean basin. Unfortunately, the recipes and fabrication techniques used during medieval times have been lost and that is why these objects have been widely studied. But until now, little was known on their optical properties. In this work it is shown that, despite the common belief, the chemical composition of the decoration (copper and/or silver nanoparticles) is not the only relevant parameter in order to explain the optical properties of lustres. By the use of optical characterization and the elaboration of a model - based on the Maxwell Garnett theory and the Abeles matrices theory for interferences -, simulated reflection spectra have been obtained in good agreement with the measured reflection spectra, confirming that the concentration of metal, the size of the metallic nanoparticles as well as the optical index of the glaze play a key-role in order to explain the coloured metallic shine exhibited by the lustres

Optical properties of lustred ceramics: complete modelling of the actual structure

International audienceLustres are a kind of ceramics from the Mediterranean basin dating from Middle Age and Renaissance times that display astonishing colorimetric properties: their colour changes with respect to the direction under which they are observed. These properties are related with the structure containing nanoparticles of noble metal produced by the potters. In fact, various effects play a role in the aspect of these ceramics: plasmon absorption, interferences and diffusion. Interferences occur in the specular direction, as is commonly seen, but also in diffuse directions. In this paper, a model able to simulate these interferential effects in the diffuse directions is developed in order to understand the optical properties of the lustres. The model integrates all the phenomena mentioned above and leads to good results in reproducing the colour effects observed. The results obtained here give some clues in order to understand the reasons that may have pushed the potters to improve and control the difficult process they were using at that time to produce those ceramics

A study of UV fluorescent emission of painting material

We presented the methodology and some of the results of the acquisition of reflectance and fluorescence spectra of about 220 specimens of egg tempera or linseed oil pictorial layers, binding mediums and varnishes. The samples were prepared by conservators of the Opificio delle Pietre Dure of Florence, Italy

Lusters of Renaissance pottery: experimental and calculated optical properties using inhomogeneous theories

Luster decoration of medieval and renaissance potteries constitutes one of the most important and sophisticated decoration techniques of the Mediterranean basin. Lusters consist in a thin layer of silver and copper nanocrystals immersed in a dielectric matrix. Different physical phenomena are responsible for the very brilliant and complex colored effect produced by the lusters. On one hand, according to the thickness of the thin layer, interferential effects occur giving rise to a classical iridescent effect. On the other hand, the nanostructure of the metallic compound leads to extra absorption, generally observed in the visible or near infrared, due to an external resonance associated with the excitation of a surface plasmon in the metallic particles. The position of this resonance, and so the color of the film, depends from many parameters, mainly: (1) the relative volume fraction p of the metal inclusions. (2) The mean size of the metal particle. (3) The shape of the particles and (4) the dielectric functions of the constituents. These two phenomena are not independent as the second one greatly affects the dielectric function of the film and, thus, its optical thickness. In this paper, the physical and optical properties of various lusters from Deruta and Gubbio (Italy) of the XVI century are presented. The structure and the composition of the different films have been determined by scanning electron microscope (SEM), ion beam analyses (PIXE and RBS) and low incidence X-ray diffraction. The optical properties have been determined by two different techniques: (a) hemispherical spectroscopic measurements under near-normal incidence; (b) gonioscopic measurements for a given angle of incidence and wavelength. The first one allows the determination of the effective index of refraction of the inhomogeneous layer, and the second one the determination of the bidirectional reflectance distribution function (BRDF) of the material

Copper red glazes: a coating with two families of particles

Abstract In order to explain the origin of the deep red color of copper glazes on ceramics, a ceramist has elaborated, by firing under reducing atmosphere, a significant number of tiles. The analysis of the structure and composition of a representative sample by TEM and EELS, followed by an optical characterization and an optical modeling using the radiative transfer approach (four-flux model) have enabled a comprehensive explanation of the origin of the color in these glazes. The presence of two families of copper nanoparticles in the vitreous matrix. The first, purely absorbing, of diameter 10-50 nm, essentially creates color by a substractive process. The second, due to its larger diameter, 100 nm or more, mainly acts on color by scattering of the visible light. Both act competitively in the layer. A color chart of all the hues which can be reached by this technique has eventually been theoretically calculated. 1

Temperature resolved reproduction of medieval lustre

Luster is a golden metallic-like decoration produced on glazed ceramics since early Islamic times (Iraq, 9th AD). Luster is obtained by the reaction of a luster paint and the glaze surface over which it is applied. A temperature-resolved XRD experiment was designed to study the high temperature reactions in the luster paint while the luster layer is formed. The luster paint composition has been made based on the original luster paints found during the excavation of the 13th AD workshop site at Paterna (Valencia). The sulfo-reducing atmosphere created during the decomposition of cinnabar promotes the reduction of Cu2+ containing compounds to Cu+ and the presence of Hg vapours delays the precipitation of metal silver. Moreover, evidence of the formation of a melt in which the copper and silver-containing compounds dissolve has also been obtained. The thickness of the luster paint applied results in the formation of luster layers of different hues and colours. The use of a mixture of copper and silver paint results in the formation of dark-brown luster layer similar to the ones produced in early Islamic times in Iraq and showed also the characteristic blue iridescence