Heterogeneous distribution of metal nanocrystals in glazes of historical pottery

It has been recently shown that lustre decoration of medieval and renaissance pottery consists of silver and copper nanocrystals, dispersed within the glassy matrix of the ceramic glaze. Lustre surfaces show peculiar optical effects such as metallic reflection and iridescence. In many cases, lustre appears overlapped to colored drawings. Here we report the findings of a study on glazes, pigments and lustre of several shards belonging to Deruta and Gubbio pottery of XVI century. The components of glazes and pigments have been identified. Lustre is confirmed to be characterised by silver and copper metal nanocrystals inhomogeneously dispersed in the glassy matrix of the glaze. In the case of lustre overlapped to colored decorations, we found two contradictory cases. The first consists of a lustre surface successfully applied over a blue smalt geometrical drawing. The second consists of a lustre surface, unsuccessfully applied over a yellow lead-antimonate pigment. The yellow pigment hinders the formation of lustre and removes crystals of tin dioxide, normally present in the glaze as opacifier.     

Evaluation of a bioluminescence method, contact angle measurements and topography for testing the cleanability of plastic surfaces under laboratory conditions

Detection of adenosine triphosphate (ATP) by bioluminescence is used, for instance, in the food industry and in hospitals to assess the hygiene status of surfaces. The aim of this laboratory study was to investigate the feasibility of the ATP method for estimating the cleanability of resilient floor coverings from biological soil. The surfaces were worn using a Soiling and Wearing Drum Tester, and soiled and cleaned with an Erichsen Washability and Scrubbing Resistance Tester. In the laboratory test carried out with the bioluminescence method, most of the new and worn floor coverings that were biologically soiled were cleaned efficiently. According to this study, the semiquantitative ATP screening method can be used for hygiene monitoring of flooring materials. No correlation was found between cleanability and contact angles or surface topography measured using a profilometer. However, by revealing local irregularities and damage on surfaces, scanning electron micrographs appeared useful in explaining differences in cleanability.     

Light scattering by complex ice-analogue crystals

Angle-dependent light-scattering measurements on single ice analogues crystals are described. Phase functions and degree of linear polarization are measured for electrodynamically levitated crystals. A procedure for randomizing particle orientation during levitation is demonstrated. The dependence of scattering on the shape, complexity and surface roughness of the crystals is examined. The phase functions from complex crystals with smooth surfaces show little dependence on shape. There is close agreement between the measured functions and the analytic phase function for ice clouds. However, rosettes with rough surfaces have qualitatively different phase functions, with raised side and back scattering. The asymmetry parameter is typically about 0.8±0.04 and 0.63±0.05 for smooth and rough crystals, respectively. The 22° halo peak is present for smooth rosettes and aggregates but absent for rough rosettes. Two-dimensional scattering patterns from several crystals in fixed orientations are also shown. The results suggest that it may be possible to use such patterns to discriminate not only between crystals of different shape but also to obtain some information on surface properties.     

Design principles for broad-spectrum protein-crystal nucleants with nanoscale pits

Growing high-quality crystals is a bottleneck in the determination of protein structures by x-ray diffraction. Experiments find that materials with a disordered pitted surface seed the growth of protein crystals. Here we report computer simulations of rapid crystal nucleation in nanoscale pits. Nucleation is rapid, as the crystal forms in pits that have filled with liquid via capillary condensation. Surprisingly, we find that pits whose surfaces are rough are better than pits with crystalline surfaces; the roughness prevents the growing crystal from trying to conform to the pit surface and becoming strained.     

Utilization of profilometry, SEM, AFM and contact angle measurements in describing surfaces of plastic floor coverings and explaining their cleanability

The tendency to soil and cleanability of ten commercial plastic floor coverings: eight vinyl (PVC) floor coverings, one vinyl composite tile and one plastic composite tile, were examined. Floor coverings were soiled with inorganic, organic and biological soil. The cleanability was measured both by bioluminescence of ATP (adenosine triphosphate) and colorimetrically. The surface topography was studied by AFM, SEM and with a profilometer. From the 2D- and 3D-profilometric measurements several characteristic parameters of the surface profiles were extracted. The tendency to soil and cleanability were compared with the characteristics of the surface. A weak correlation was found between roughness and soilability but no correlation between roughness and cleanability. Roughness had no correlation with contact angle.     

Effect of plasticizer and surface topography on the cleanability of plasticized PVC materials

A quantitative radiochemical measuring procedure was used to investigate soil adhesion on laboratory-made polyvinyl chloride (PVC) surfaces. The materials contained different plasticizers and microstructures. Both the quality and amount of plasticizers and the microstructure affected the cleanability of the PVC samples. The surface topography and structures were examined with a contact angle meter, atomic force microscopy (AFM) and a contact profilometer.     

Characterisation of decorations on Iranian (10th–13th century) lustreware

It has been recently shown that lustre decoration of Medieval and Renaissance pottery consists of silver and copper nanoparticles, dispersed within the glassy matrix of the ceramic glaze. Lustre surfaces show peculiar optical effects, such as metallic reflection and iridescence. Here we report the findings of a study on lustred glazes of several shards belonging to Iranian pottery of the 10th and 13th centuries, decorated on both sides. Two different glazes, depending on the side of the sample, have been identified. Different lustre chromatic effects are characterised by the relative presence of silver- and copper-metal nanoparticles dispersed in the glassy matrix. PACS 61.46.+w     

Anisotropic surface melting in lyotropic cubic crystals

From experiments with ice or metal crystals, in the vicinity of their crystal/liquid/vapor triple points, it is known that melting of crystals starts on their surfaces and is anisotropic. It is shown here by direct observations under an optical microscope that this anisotropic surface melting phenomenon occurs also in lyotropic systems. In the case of C12EO2/water mixture, it takes place in the vicinity of the peritectic Pn3m/L3/L1 triple point. Above the peritectic triple point, where the Pn3m and L1 phases coexist in the bulk, the surface of a Pn3m-in-L1 crystal is composed of (111)-type facets surrounded by rough surfaces. The angular junction suggests that rough surfaces are wet by a L3-like layer while facets stay “dry”. This is analogous to the pre-melting at rough surfaces in solid crystals. Upon cooling below the peritectic triple point, where L3 and L1 phases coexist in the bulk, a thick layer of the L3 phase grows from the pre-melted, rough Pn3m/L1 interface. Simultaneously, facets stay dry and their radius decreases. In this tri-phasic configuration, stable in a narrow temperature range, the L3/L1 and L3/Pn3m interfaces have shapes of constant mean curvature surfaces having common borders: edges of facets.     

Speckle correlation for the analysis of random processes at rough surfaces

The importance of technological processes like corrosion, ablation or deposition causes interest in the quantitative monitoring of changes at rough surfaces. Thus, there is a need for effective methods to measure the statistical parameters characterizing changes in the profile or the material composition of such objects. The speckle field scattered from the surface is used as information carrier and its change is measured by correlation. This is realized by sophisticated data acquisition and digital processing techniques. An important issue is the interpretation of the correlation output in terms of statistical parameters describing the surface change. For many random surfaces a geometrical relation between surface profile and optical phase proves satisfactory. This allows to determine the standard deviation of the profile change. For a verification, speckle decorrelation in model surfaces of known deviation is measured. The paper introduces the speckle correlation concept, outlines some history and current setups and describes methods for data evaluation. The reliability of the quantitative interpretation of the speckle decorrelation is demonstrated. The method is illustrated by studies of metal corrosion and material removal in the cleaning of historical objects by laser ablation.     

Step structure on the fivefold Al-Pd-Mn quasicrystal surface, and on related surfaces

We compare step morphologies on surfaces of Al-rich metallic alloys, both quasicrystalline and crystalline. We present evidence that the large-scale step structure observed on Al-rich quasicrystals after quenching to room temperature reflects equilibrium structure at an elevated temperature. These steps are relatively rough, i.e., have high diffusivity, compared to those on crystalline surfaces. For the fivefold quasicrystal surface, step diffusivity increases as step height decreases, but this trend is not obeyed in a broader comparison between quasicrystals and crystals. On a shorter scale, the steps on Al-rich alloys tend to exhibit local facets (short linear segments), with different facet lengths, a feature which could develop during quenching to room temperature. Facets are shortest and most difficult to identify for the fivefold quasicrystal surface.     

Raman spectrometry,a unique tool to analyze and classify ancient ceramics and glasses

Raman micro/macro spectroscopy allows a non-destructive remote analysis: body and glaze, crystalline and amorphous phases can be identified, including the nanosized pigments coloring the glaze. Last-generation instruments are portable, which allows examination in museums, on archaeological sites, etc. This paper gives an overview of the potential of the Raman-spectrometry technique to analyze ancient ceramics and glasses. Selected glasses as well as glazes of various porcelains, celadons, faiences and potteries, representative of the different production technologies used in the Ancient, European, Mediterranean, Islamic and Asian worlds, were studied. Their identification is based on the study of the Raman fingerprint of crystalline and glassy phases. Raman parameters allow for the classification as a function of composition and/or processing temperature. Special attention is given to the spectra of amorphous and coloring phases (pigments). PACS 81.05.Kf; 81.70.Fy; 81.05.Je; 01.65.+g     

Ratchet effect in faceting

The paper deals with a new phenomenon, named ratchet effect, envisioned theoretically as a likely consequence of metastability of crystal facets and expected to occur upon a temperature cycling. In experiments, Pn3m lyotropic crystals surrounded by the isotropic L1 phase in the mixture C₁₂EO₂/water are used. At equilibrium, the Pn3m/L1 interface contains small (111)-type facets in coexistence with rough surfaces. In agreement with theoretical expectations, it is shown that upon a saw-tooth-shaped temperature cycling, facets are growing until the rough surfaces are completely eliminated. A model of the ratchet effect is proposed.Received: 8 January 2004, Published online: 25 March 2004PACS: 64.70.Md Phase transitions in liquid crystals - 68.35.Md Surface thermodynamics, surface energies - 61.30.-v Liquid crystals     

Synchrotron radiation micro-XRD in the study of glaze technology

The production of glass represented an important technological achievement, and it was the starting point for the invention of a large variety of materials, produced by processes involving melting, partial or total, and precipitation of new crystalline compounds during cooling. In particular, those crystallites built-in the glaze due to partial or total insolubility of some elements originally present in the melt (for instance some colourants and opacifiers), as well as those crystallites formed in the glazes resulting from the interaction of the melt and the ceramic surface are subject of the highest interest in the study of glaze technology. Finally, devitrification and weathering gives rise to precipitation of new crystalline compounds closer to the surfaces and interfaces.     

Reactivity of chromium-based pigments in a porcelain glaze

This paper presents a comprehensive investigation at the microscopic scale of various pigments composed of chromium from the French ‘Manufacture de Sèvres’ to establish the origin of color in glazes. Electron microscopy coupled with X-ray diffraction allows the determination of the microstructure and composition of the crystalline phases after firing. X-ray absorption spectroscopy reveals subtle changes in the medium-range ordering around Cr with high spatial resolution, in the pigment grain or at the pigment/glass interface. Principal results indicate systematic and common changes whatever the pigment types: (i) Cr-enrichment for the final crystals, that controls the coloration of the glaze, (ii) migration of specific elements such as Al or Zn from the pigments to the amorphous part of the glaze, and (iii) crystallization of anorthite in the near proximity of the altered Cr-bearing crystalline pigments.     

Phonons in disordered solids. II. Thermodynamic properties

For model disordered crystals we show that Debye theory yields the correct low-temperature specific heat if the measured low-frequency speed of sound is used in the calculation of the T³ term. This contrasts with the anomalous leading T term and other anomalies of amorphous or glassy materials, sugesting that thermodynamic properties might be useful in distinguishing a disordered-crystal phase from the amorphous or glassy phase. Our results make it plausible that below a threshold amount of disorder all thermodynamic properties are basically those of an elastic crystalline phase, while above this threshold value, they belong to a distinct phase, dependent on nonlinearities for its stability.     

Molecular dynamics study of the equilibrium flux of gas molecules to a fractal/rough surface: Effects of gas atom diameter

The frequency of collisions of ideal gas molecules (argon) with a rough surface has been studied. The rough/fractal surface was created using the random deposition technique. By applying various depositions the surface roughness was controlled and, as a measure of irregularity, the fractal dimensions of the surfaces were determined. The surfaces were next immersed in ideal gas and the numbers of collisions with these surfaces were counted. The calculations were carried out using the simplified molecular dynamics simulation technique (only hard core repulsions were assumed). The calculations were performed for various ratios of gas phase atoms diameter to the surface substrate atoms diameter. The results obtained showed that the size of a gas phase atom has crucial influence on the relation between the frequency of collision and the surface fractal dimension     

LIBS used as a diagnostic tool during the laser cleaning of ancient marble from Mediterranean areas

The use of laser ablation for cleaning stone is a tried-and-tested method for preserving outdoor artwork surfaces exposed to environmental stresses. However, it is of interest to spectroscopically characterize the sample surface before and during the laser ablation in order to implement automatic control of the cleaning process. To this aim, we have undertaken systematic LIBS analysis on various clean and dirty surfaces of marble fragments collected from ancient quarries in Mediterranean areas, without the characteristic patina that comes from the protective layers usually deposited on the final artwork. The effectiveness of the cleaning process was then monitored by following the disappearance from the LIBS spectra of the encrustation elements during successive laser shots. The LIBS analysis of the clean surfaces of the samples examined confirmed that main bulk composition is based on calcium and magnesium carbonates, with the addition of strontium and, to a minor extent, of manganese and copper substituents. On the other hand, the encrustations were rich in sodium, aluminum, iron, silicon, titanium, lithium, manganese, and chromium, probably coming from sand/soil deposition and, only to a minor extent, from atmospheric pollution. Although SEM imaging and SEM-EDX analyses performed on the same samples at different resolutions showed remarkable surface inhomogeneities from the crustal region deep into the bulk material, the work demonstrates the possibility of a quantitative, minimally invasive, LIBS stratigraphy. The results from the technique are suitable for monitoring cleaning processes by determining appropriate elemental markers present on the surface at trace level (of the order of 100 ppm). PACS 52.25.Kn; 7.60.Rd; 32.30.Jc; 42.62.Fi     

Preparation Principle of Super-Hydrophobic Surfaces by Phase Separation

The Flory–Huggins theory of polymer solutions combined with an evaporation process was employed to interpret the preparation mechanism of a super-hydrophobic surface by phase separation. The ternary phase diagram of a polymer/solvent/nonsolvent was calculated by using the solubility parameters of the components in the system. It indicated that with the increase of the nonsolvent fraction, the initial volume fraction of the polymer or the evaporation rate of the solvent, the evaporation time for phase separation would shorten and the phase separation rate would speed up. The polymer volume fraction in the dense phase would increase and the precipitating particles tended to collide and aggregate, resulting in a rough, super-hydrophobic surface. Experimental results were in agreement with this principle of phase separation for preparing super-hydrophobic surfaces. Membranes of acrylic resin and fluorinated acrylic resin with rough surfaces were successfully obtained by the phase separation method. Especially, the water contact angle of the fluorine-containing acrylic resin with the rough surface was greater than 150°, which satisfied the requirement of super-hydrophobicity.