A two-way analytical investigation of ancient gold coins: Elemental and colorimetric description of precious materials.

The investigation of ancient artifacts is often constrained by their scarce availability and high protection and custody protocols. Among these, coinage represents an especially valuable kind-of-samples given their uniqueness and the subjacent information that is hidden behind their composition. Their analysis are often carried out using non-destructive techniques in order to avoid any alteration of the samples. In the field of Cultural Heritage analysis, smartphone-based methodologies have experienced a significant increase during the last few years, given their wide availability and ability to yield fast results. However, their analytical application demands a thorough and careful tuning during the methodology optimization. In this work, 21 historical gold and golden coins spanning a historical period of more than 2000 years have been analytically investigated. To that end, a two-fold approach has been implemented: first, the elemental composition has been analysed using portable X-ray fluorescence; and second, an innovative smartphone-based imaging method has been applied to measure their colour. Results allowed to describe the coins from their elemental profile, identifying some potentially debased ones, as well as some others not containing any gold. When possible, the results have been compared to previously reported cases, but our samples include some previously unreported cases representing new insights. All in all, this article provides new analytical data on unanalysed unique historical samples, in terms of their elemental profile and colorimetric properties, making use of an innovative, non-invasive nor destructive, fast and affordable colorimetric smartphone-based method to characterise historical coins.

A smartphone image-based method for the colorimetric characterization of historical pigments in mural paintings.

In this article, the detailed description of a smartphone-based analytical method to turn a smartphone into a colorimeter is described and applied to mural painting replicas. The method consists of a camera characterization process, to estimate CIELAB values from RGB camera responses, correcting for potential experimental interferences, like the effect of the lighting/capture geometry or software for color modification and enhancement. Next, the estimated CIELAB descriptors were used to build a chemometric Support Vector Classifier to objectively distinguish among the colors of the different pigments. The method was validated in terms of color reproduction and classification performance.•A smartphone-based method is described to capture mural painting color.•A color gamut-specific camera characterization procedure is developed and the performance of the smartphone-based colorimeter is compared with a spectrophotometer.•A classification method based on the estimated CIELAB descriptors is validated in terms of classification performance.

Unveiling origins, composition, and appearance of ancient Islamic gold coins through elemental and smartphone-based colorimetric studies.

In this article, the Islamic gold coins collections of the University of Valencia is studied for the first time for its elemental composition and colorimetric properties. To that end, non-destructive elemental analysis using energy-dispersive X-ray fluorescence is applied to obtain the coins' elemental profile. Additionally, the colour of the coins is assessed using smartphone-based colorimetry as an innovative non-invasive method. Results indicate that the Islamic coins could be attributed to Almoravids, and the gold origin could be the famous Sudanese gold, an ore which was valued all over the world. Also, the text found in the coins was translated and allowed to objectively identify the mint and year. Based on these results, it can be seen that the earliest coins struck in the Iberian Peninsula are characterised by slightly lower gold concentrations than the ones struck in the northern part of Africa, pointing towards a potential recycling of coins which already circulated in the area. In conclusion, this work provides new analytical insights into a peculiar and unique type of samples, allowing to draw some conclusions in terms of their origins and materials, and for the first time allows to characterise the chromatic coordinates of this type of samples.

Factors affecting the benefit of glasses alone in treating childhood amblyopia: an analysis of PEDIG data.

BACKGROUND: To evaluate factors associated with better outcomes from optical treatment alone in amblyopic children from 3 up to 7 years. METHODS: Data extracted from two studies with similar protocols, Amblyopic Treatment Studies 5 (n = 152) and 13 (n = 128) from the Pediatric Eye Disease Investigator Group database, were used to determine by regression analysis the factors associated with improvements in visual acuity in the amblyopic eye, inter-ocular visual acuity difference and stereoacuity. Input variables were aetiology of amblyopia (anisometropic, strabismic and combined-mechanism amblyopia), treatment compliance, visual acuity, interocular visual acuity difference, stereoacuity, tropia size at distance and near, age and refractive error at baseline. RESULTS: Despite the range of clinical factors considered, our models explain only a modest proportion of the variance in optical treatment outcomes. The better predictors of the degree of optical treatment success in amblyopic children are visual acuity of the amblyopic eye, interocular visual acuity difference, stereoacuity, treatment compliance and the amblyopic eye spherical-equivalent refractive error. While the aetiology of the amblyopia does not exert a major influence upon treatment outcome, combined-mechanism amblyopes experience the smallest improvement in visual acuity, tropia and stereoacuity and may need longer optical treatment periods. CONCLUSIONS: While results identify the factors influencing optical treatment outcome in amblyopic children, clinicians will be unable to predict accurately the benefits of optical treatment in individual patients. Whether this is because relevant clinical or non-clinical factors (e.g. nature and volume of daily activities undertaken) influences the outcomes from optical treatment has not yet been identified and remains to be discovered.

Spectral Transmission of the Human Corneal Layers.

We have assessed the spectral transmittance of the different layers of the human cornea in the ultraviolet (UV), visible, and near-infrared (IR) spectral ranges. Seventy-four corneal sample donors were included in the study. Firstly, the corneal transmittance was measured using a spectrophotometer. Then, all samples were fixed for histopathological analysis, which allowed us to measure the thickness of each corneal layer. Finally, the absorption coefficients of the corneal layers were computed by a linear model reproducing total transmittance. The results show that corneal transmission was almost in unity at the visible and IR ranges but not at the UV range, in which the layer with higher transmission is Descemet's membrane, whereas the stroma showed the lowest transmittance. Regarding the absorption coefficient, the most absorptive tissue was Bowman's layer, followed by the endothelium. Variations on transmittance due to changes in the stroma, Bowman's layer, or Descemet layer were simulated, and important transmission increases were found due to stroma and Bowman changes. To conclude, we have developed a method to measure the transmittance and thickness for each corneal layer. All corneal layers absorb UV light to a greater or lesser extent. The absorption coefficient is higher for Bowman's layer, while the stroma is the layer with the lowest transmittance due to its thickness. Variations in stroma thickness or changes in the corneal tissue of Bowman's layer or the endothelium layer due to some pathologies or surgeries could affect, to a greater or lesser degree, the total transmission of the cornea. Thus, obtaining accurate absorption coefficients for different layers would help us to predict and compensate these changes.

Technical Report: Repeatability of Contrast Sensitivity Test in Children.

Contrast sensitivity (CS) in children is not routinely measured in the clinical setting, although CS losses have been found in amblyopic and premature children. Thus simple visual acuity measurements do not completely assess their quality of vision. To evaluate contrast sensitivity in children, a reliable and easy test, sampling the entire spatial frequency range, is necessary. PURPOSE: This study aimed to evaluate the repeatability and normal range of the contrast sensitivity function measured using the Topcon CC-100 instrument, in children aged between 4 and 9 years, for use as a diagnostic tool. METHODS: Contrast sensitivity was measured in 25 children, 11 boys and 14 girls, with normal or corrected-to-normal visual acuity, normal binocular function, and stereopsis. Two measurements were performed, 3 months apart, with a Topcon CC-100 device using achromatic sinusoidal gratings of 1.5, 3, 6, 12, and 18 cycles per degree (cpd) with random orientation in a circular window with sharp edges. RESULTS: The normal range in the first visit is wider than in the second. Coefficients of variation are better for the middle-range spatial frequencies (6.6 and 7.8% at 3 and 6 cpd, respectively) and worst at 18 cpd (18.2%), with intermediate values at 1.5 cpd (11.3%) and 12 cpd (13.7%), and better for older than for younger children. No significant sex differences were found (P > .05, Mann-Whitney U test). CONCLUSIONS: Repeatability measured by the coefficient of variation is better for the middle frequency range (3 and 6 cpd) than for low (1.5 cpd) and high frequencies (12 and 18 cpd). The variability of the differences between the first and second measurements suggests that the participants were not able to maintain a stable response criterion. The test seems to be subject to a learning effect, and the standard normality range may not be adequate for children.