Colour assays: An inside look into Alentejo traditional limewash paintings and coloured lime mortars

A series of colour assays were conducted taking into account old bibliographic recommendations and oral testimony regarding traditional lime painting technology from the Alentejo (South Portugal) region. The main objectives were: (a) the colorimetric analysis of paintings made with different limewash preparation methods; (b) the comparison between natural processed red and yellows ochre pigments (“home made” and from industrial origin) and synthetic iron oxides in different concentrations and lime proportions; (c) the evaluation of the colorimetric CIELAB coordinates during the lime carbonation process in coloured mortars and limewashes. The results shows that the evolution of L*, a*, and b* during the carbonation process is independent of pigment concentration and paint thickness but dependent of pigment composition and finishing technique (lime painting or coloured mortar). They also emphasize the importance of surface appearance attributes and its influence on the colorimetric parameters. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 61–71, 2011     

Effect of particle size on pigments colour

The historical pigments, contrary to modern ones, are not constituted by particles having all the same size and this influences the colour of the paint layers. The hiding power and colouring power of a pigment depends, in fact, on its particle size. The aim of this study was to evaluate the influence of particle size on optical characterization of paintings in terms of reflection of light and related colour specification. Starting from the qualitative observation, we have attempted to quantify the pigments colour variations induced by grinding and then attributable to granularity. Powdered pigments of principal colours have been selected in specific particle size range by mechanical sieving. The measurements were performed both on pigment pellets and on paintings realized with binder casein. All samples were characterized by an optical and colorimetric point of view through spectrophotometric analysis and for the surface morphological observation through scanning electron microscopy. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 236–243, 2017     

Chromaticity changes of inorganic pigments in Chinese traditional paintings due to the illumination of frequently‐used light sources in museum

Optical radiation can cause permanent damage to the color of Chinese traditional paintings, which have extremely high responsivity in the museum illumination. In order to obtain quantitative influence laws of artificial illumination on inorganic pigments in Chinese traditional paintings and provide basis for choosing light sources, a long periodic illumination experiment was carried out to examine how prolonged exposure of three light sources (tungsten halogen, metal halide and white light emitting diodes), frequently‐used in museums, affect the chromaticity of five inorganic pigments [azurite (blue), cinnabar (red), orpiment (yellow), ancient graphite (black), clam shell powder (white)], commonly used in Chinese traditional paintings. Through the experiment, we found that the illumination causes a color change to inorganic pigments, and the degree of which is related to the photochemical stability of pigments and the high energy shortwave radiation in the light source spectrum. We also obtain the color change laws of the five pigments and the quantitative relationships of color damage for different painting types. These results can provide data basis for related research on Chinese traditional painting illumination and choice basis for light sources in museum lighting designs.     

Digitally reconstructing Van Gogh's Field with Irises near Arles part 3: Determining the original colors

In earlier articles, we determined the spatial distributions and concentrations of all pigments used by Van Gogh in his painting Field with Irises near Arles. The colors of some pigments are expected to have changed over time, especially those of chrome yellow, cochineal, and eosin lake. For all pigments in this painting, we made physical paint reconstructions by following historical sources on raw materials and production processes, and we determined their optical properties. We combined this with pigment concentration maps to reconstruct the original colors of the painting digitally. When substituting the reconstruction paints into the calculations, we found that technical‐scientific data was not sufficient to resolve several issues. In those cases, discussions within the broad interdisciplinary team allowed us to make informed decisions. These issues refer to the representation of the sky area, and the original contributions of the red lake pigments to local colors. The digitally reconstructed colors of the painting show that due to discoloring of red lake pigments, the irises in the field have changed from a warm purple to purplish blue, and many pink spots in the field have turned to white. The range of yellows in the field has decreased and partly turned to dark brown. The digital reconstruction gives a better understanding of the color scheme used by Van Gogh when compared to remarks the artist made in letters when describing this painting. Also, the original color composition is seen to be aligned with color theories on which Van Gogh based his work.     

Influence of vehicle on historical pigments colour

The colour of a paint layer is determined by the pigments mixed with a vehicle and painted on a support. According to their chemical nature, the vehicles are substances that, after drying or hardening, produce an uniform and homogeneous layer. With the aim of quantifying the influence of the medium on the specification of the painting colour, we realized samples of paintings. We considered pigments and dyes of the artist's hues using the vehicles typical of ancient times: oils (especially linseed and poppy oils), casein and egg yolk, mixed according to old recipes. Measurements were performed by reflectance spectrophotometry observing the Spectral Reflectance Factor (%SRF) trend and calculating colour changes. The colorimetric study was carried out in the CIELAB colour space related to the CIE 1964 standard observer and with the D65 illuminant. The results were evaluated also on the basis of the distribution of pigment particles on paint layers observed by scanning electron microscopy.     

新型多彩涂料的研制

研制成一种兼具壁纸、涂料功能的新型装饰性多彩涂料，适用于内墙涂装。该涂料不同于一般多彩涂料，可省去部分分散设备和保护胶分散相，是由底涂漆、中涂漆和面漆组成。介绍了该底涂漆、中涂漆和面漆的制备。讨论了涂料用树脂、助成膜剂和珠光颜料对涂料的影响。     

Cool and photocatalytic yellow ceramic pigments; from lead-tin to Cr doped scheelite pigments

The historical lead based pigments (XVII-XVIII century), the modern Ni,Sb-rutile (1939) and Pr-zircon (1961) yellow pigments as well as the novel yellow pigments based on Cr-scheelite and Mo-yttrium cerate pigments were synthesized and compared as semiconductors of high NIR reflectance (cool pigments) and with photocatalytic activity. All powders are wide band gap semiconductors (E_g=2.1–3.1?eV) with high NIR reflectance, ranging from 80% for Cr-Scheelite to 86% of Naples yellow, except Ni,Sb-rutile pigment that shows 55%. The low color performance of lead based pigments in alkyd paint and lead-free glazes along with its toxicity, discard these pigments as cool eco-friendly pigments. The Pr-zircon, Cr-scheelite and Mo-yttrium cerate pigments exhibit high NIR reflectance (R_NIR =?80–83%) and yellow coloration (b*?=?57.6–45.3) but only Pr-zircon and Cr-scheelite show color stability in alkyd paint and lead free glaze applications. Regarding to results of Orange II photodegradation test, lead based and Ni,Sb-rutile pigments inhibits the photolysis of the UV irradiation, acting as protecting agents from irradiation. The Mo-cerate shows a slight photocatalytic activity (t_1/2 =?301?min) and both Cr-scheelite and Pr-zircon pigments show a moderate activity (t_1/2 =?198 and 184?min respectively). Looking at a possible industrial application, the leaching test shows that the fluorides released by Pr-zircon (16.8?mg/g) as well as the Cr(VI) of Cr-scheelite (6?mg/g) should be treated and controlled. The Cr-scheelite solid solution Ca(Cr_xW_1-x)O₄ is stable to x?=?0.2 but its pigmenting capacity saturates at x?=?0.1.     

Reaction of thiobarbituric acid with saturated aldehydes

The reaction of thiobarbituric acid (TBA) with saturated aldehydes, i.e., 1-butanal, 1-hexanal and 1-heptanal, produced a 455-nm yellow and a 532-nm red pigment. Formation of the pigments depended on the reaction conditions. The yellow pigment was unstable in the presence of excess amounts of the saturated aldehydes. The red pigment was formed only when the reaction was performed at a TBA/aldehyde ratio of 1∶1 in aqueous acetic acid. Formation of the yellow and red pigments required molecular oxygen. The colorless adducts, intermediates for the yellow and the red pigments, were isolated from the reaction mixtures. Aldol condensation and dehydration of 2 mol of the saturated aldehydes initially gave the α,β-unsaturated aldehydes, which in turn reacted with TBA to form the colorless adducts, pyranopyrimidine derivatives. The adducts were then converted into the yellow and red pigments under aerobic conditions.     

Pigments extracted from the wood‐staining fungi Chlorociboria aeruginosa,Scytalidium cuboideum,and S. ganodermophthorum show potential for use as textile dyes

A growing interest in the use of naturally produced pigments for textile dyeing has led to increased efforts towards the identification of such pigments that are less toxic, more sustainable, and more stable over time than currently used synthetic compounds. This work utilised various concentrations of green, red, and yellow pigments extracted with dichloromethane from the wood‐staining fungi Chlorociboria aeruginosa, Scytalidium cuboideum, and S. ganodermophthorum, respectively, for the effective dyeing of bleached cotton, spun polyamide (nylon 6.6), spun polyester (Dacron 54), spun polyacrylic, and worsted wool. All three pigments utilised in this study show significant potential for use as textile dyes. Colour changes suggested that drip application methods were superior to submersion using dichloromethane. Colour changes as compared with the untreated fabrics were most significant on polyester, which is likely due to increased levels of polymer swelling in polyester exposed to dichloromethane.     

Material and diagnostic characterization of 17th century mural paintings by spectra‐colorimetry and SEM‐EDS: An insight look at José de Escovar Workshop at the CONVENT of Na Sra da Saudação (Southern Portugal)

The early 17th century mural paintings set from the low‐choir of the extinct Dominican Convent of Nossa Senhora da Saudação in the town of Montemor‐o‐novo were analyzed by a setup comprising visible spectra‐colorimetry and scanning electron microscopy coupled with energy dispersive X‐ray spectrometry (SEM‐EDS) complemented with optical microscopy (OM), micro X‐ray diffraction, micro FTIR, and micro Raman spectroscopy. The main goals were material and diagnostic characterization of the paint layers and pictorial techniques used by Jose de Escovar workshop, one of the most active and controversial easel and mural painters of Evora Archiepiscopate between 1585 and 1622. The results show a differentiate use of red, blue, and green pigments in an alkaline environment. Stable mercury sulfide (HgS) was identified in almost all red areas in the latest scenes while, in the first ones, red ochre (Fe₂O₃) is the predominant pigment. Faded smalt (a co‐potassium silicate glass) is present pure in the sky background or mixed with red ochre in the garments at the beginning of the low‐choir but less at the end. Five kinds of copper‐based materials, with different degrees of color alteration, were found, namely malachite and azurite, copper chlorides, copper sulfates (e.g., posjnakite), and pseudomalachite. Another curious feature is the uneven use of a limewash made with slaked calcitic lime in the carnations. Lack of material, internal organization strategies, or technical differences within the team are probably the most likely causes. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 288–306, 2014; Published Online 5 February 2013 in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/col.21792     

Lightfastness assessment of Levantine rock art by means of microfading spectrometry

The documentation of archeological sites requires the adoption of non‐destructive techniques to safeguard the unique legacy coming from prehistoric periods. This article tackles the assessment of lightfastness properties on a rock art site to determine the behavior of motif's color deterioration over time in Remígia Cave, Castellón (Spain), which is considered part of a UNESCO World Heritage Site. The measurements were performed using a microfade testing device to analyze the spectral characteristics and the aging properties of the colorant system and various substrates on site. Two scenarios have been identified depending on whether the lightness (L*) parameter of the rocky substrate changes or not in relation with the painted motifs. If the substrate remains stable without any change, red motifs containing iron oxide pigments will become more visible. If the substrate becomes lighter, the pigments will experience similar changes. Therefore, the contrast between paintings and support will be considerably enhanced.     

高含水油田管道内壁涂料的研制

以环氧树脂、防腐颜填料等原材料研制了具有高效防腐性的底漆;以氟树脂、二硫化钼、聚四氟乙烯、石墨等原材料研制了不仅具有防腐蚀特性,同时具有疏水等特性的低表面能面漆.由所研制的底漆和面漆组成的复合涂层在注水原油在管道输送过程中,对管道底材起到很好的保护作用,延长了管道的使用寿命,同时面漆涂层的表面能比较低,具有一定的疏水性,能够减小管道中液体流动的阻力,从而达到减阻增效的作用.     

Solventborne paint systems on carbon steel and hot-dip galvanized steel for a wide range of atmospheric exposures

The paper analyzes the performance of solventborne paint systems applied on carbon steel and hot-dip galvanized steel in a wide range of atmospheric exposures. The study has involved paint systems exposure for 3.5 years in eight natural atmospheres. The atmospheric conditions cover from temperate rural climates to tropical severe marine and Antarctic coastal regions. The paint systems included several alkyds formulated with a variety of pigments (anticorrosive and barrier), epoxies, chlorinated rubber, and zinc-rich (ethyl silicate and epoxy). It has been concluded that in rural and urban atmospheres alkyd systems afford equivalent anticorrosive protection of steel to the epoxy/polyurethane system. The toxic red lead pigment may be replaced in long linseed-oil alkyd primer paints by non-toxic pigments, such as a mixture of micaceous iron oxides (MIO) and black iron oxides or zinc phosphate, without affecting the anticorrosive properties of the paint system. In aggressive atmospheres (industrial, marine), paint systems including zinc-rich primers or applied on galvanized steel must be used, especially in surface regions with coating faults (scribes).     

Digitally reconstructing Van Gogh's Field with Irises near Arles. Part 2: Pigment concentration maps

Colors in many paintings of great art historical value have changed over time, due to the combined effects of natural ageing, accumulated surface grime, and materials added during later conservation treatments. The physical restoration of the colors in such paintings is not possible. This article describes one part of work done to digitally restore the colors of Van Gogh's painting Field with Irises near Arles, dating from May 1888. We have used multispectral reflectance data to estimate absorption K and backscattering S parameters of Kubelka‐Munk 2‐constant theory. This was done for all 13 pigments known to have been used by Van Gogh in this painting, and based on this the concentration maps for each of these pigments were calculated. We validated the calculated concentration maps in several ways. For some pigments, we were able to predict spots on the painting where the pigment is expected to occur in unmixed form based on visual examination. For several other pigments, the concentration maps could be shown to agree with XRF data. Finally, for some other pigments the concentration maps were supported by additional evidence from microscopic examinations, remarks in Van Gogh's letters and from early color reproductions. For the 1.7 million pixels for which multispectral data is available, the average color difference between the calculated and measured spectral reflectance curves is CIEDE2000 = 1.05. This further confirms that the Kubelka‐Munk calculations are well suited to describe the variety of spectral reflectance on the painting.     

Acid rain effects on the exterior durability of architectural coatings on wood

Acid rain is an important consequence of pollutants generated by modern industrial societies and is known to cause damage to ecological systems, construction materials and cultural artifacts. The assessment of the damage caused to paint films has included laboratory, exposure chamber, and exterior weathering experiments. This study uses visual assessment of paints applied directly to southern yellow pine and exposed at 30° south to either natural acid rain or deionized water spray sites in North Carolina and Ohio to determine damage by acid rain. An acrylic latex paint with a pigment volume concentration (PVC) of 52 and a volume solids (VS) of 35% was formulated with calcium carbonate or sodium potassium alumino-silicate extenders. This high PVC paint formulation is one known to stress the binding capacity of the latex and thus produce early grain cracking failures over bare wood. Major effects observed include severe yellowing and increased mildewing of the carbonate containing paints exposed to acid rain. While acid rain can damage exterior paints, much of the damage can be minimized by careful selection of the polymers and pigments used in the formulation.     

An improvement of color electrophoretic paint via ultrafine modified pigment paste

The ultrafine paste used in electrophoretic paint was prepared via ultrasonic method with pigment yellow 83 (P.Y.83), octadecyl dimethyl benzyl ammonium chloride, and deionized water. The average particle size of the ultrafine paste was only 196?nm and zeta potential was 30?mV with ultrasound for 30?min and 2?wt.% cationic dispersant. The conductivity of the paint was improved as the cationic dispersant increased. Centrifugal stability of the paint with ultrafine paste reached the maximum at 2?wt.% cationic dispersant. Compared with the performances of cathodic electrophoretic paint with the ultrafine yellow paste, the anodic film was smooth, uniform, and neat with 0.5?wt.% cationic dispersant in the ultrafine yellow paste. Deposited amount of the anodic film was 27?g/m², which was higher than the cathodic film. The curing property, adhesion, and chemical resistance of the cathodic film were better than the anodic film. Properties of five color cathodic paints (blue, yellow, red, black, and green) were discussed and were compared with the film of electrophoretic paint containing commercial pastes. Except the green film, the blue, yellow, red, and black films were smooth, fine, and uniform, and also provided good L-effect. The deposited amount of these films with excellent adhesive force was about 14–19?g/m². The electrophoretic paints containing modified pigment pastes and commercial pigment pastes present good adhesion and chemical resistance.     

Application of multiflux theory based on scattering by nonspherical particles to the problem of modeling optical characteristics of pigmented paint film: Part II

Scattering characteristics of three model systems analogs to red, green, and white pigments containing nonspherical particles are calculated with the T‐matrix method. These scattering parameters are then used to evaluate colorimetric curves of paint films with the multiflux computational technique. Color difference of each system containing different oblate spheroidal‐shaped pigments is calculated with reference to systems containing spherical pigments of equivalent volume. Results show that color‐difference increases for chromatic pigments as shape of pigments deviates from sphericity. Nonabsorbing particle analogs to titanium dioxide behave like spherical particles, though their shape deviates significantly from sphericity. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 308–316, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10165     

Energy transfer between fluorescent organic pigments

Energy transfer between fluorescent organic pigments (fluorophors) dispersed in a paint vehicle was studied for mixtures of a yellow, a red, and an orange fluorescent pigment, and for mixtures of these with titanium dioxide. Radiative energy transfer occurs among the fluorophors, but not between them and titanium dioxide A shift to longer wavelengths of the emission peak of a fluorophor with increasing paint-film thickness was noted and was ascribed to reabsorption and reemission of fluoresced radiation within the overlapping excitation and emission region typical of these organic fluorophors.     

Characterization of waterborne acrylic based paint films and measurement of their water vapor permeabilities

Recently, production of waterborne coatings has increased significantly as a consequence of strict pollution regulations. Waterborne coatings are sensitive to humidity, thus, their barrier properties with respect to permeation of moisture needs to be determined. Among various coating constituents, binder represents the matrix structure and its amount relative to the amounts of pigments and fillers can significantly affect the structure, hence the barrier property of the coating. In this study, waterborne acrylic based paints applied as protective coating on interior and exterior wall of the buildings are studied. The paint samples formulated with four different binder contents by a commercial paint company are used in the experiments. We first determine unknown ingredients of the paint samples using different characterization tools and then investigate the effect of the binder content on the structure of the paint films. In addition, water vapor permeability of the paint films is measured using a permeation cell. Results show that the barrier property of the waterborne acrylic based paint films against humidity decreases with decreased binder content due to uneven distribution of the pigments, consequently, porous structure formation in the films.     

Color changes in wall paintings under the influence of consolidation with synthetic polymers

The aim of this study is to estimate changes of color of wall paintings under the influence of one of the basic conservation procedures, that is, paint layer consolidation due to degradation of the original binder. Since the 1960s, wall paintings have been consolidated almost routinely with synthetic polymers. As the research on the subject progressed, many flaws of these products were observed. Extensive research was conducted with the aim of determining the actual impact of synthetic binders on paint layer properties. The article discusses the results from only one group of tests associated with color change measurements. Three painting techniques were selected for the study, representing a variety of original techniques common in Poland: lime, lime casein, and animal glue, as well as five commercial synthetic products predominantly employed for painting consolidation by the Polish conservation community. We are focusing on color changes taking place as a result of consolidation and subsequent from the progress of degradation.