Paint Research Articles

Easy-to-Make Polymer Hydrogels by UV-Curing for the Cleaning of Acrylic Emulsion Paint Films.

The cleaning of acrylic emulsion paint surfaces poses a great challenge in the conservation field, due to their high water sensitivity. In this article, we present easy-to-make polymer hydrogels, made by UV-photopolymerization, that show excellent cleaning properties. The formulation of hydrogels obtained by UV-curing and their performance as dry cleaners for acrylic paints was investigated. First, different hydrogel formulations based on functional acrylic monomers were used to formulate a series of UV cross-linked hydrogels by fast UV photopolymerization. Their effectiveness on surface dirt removal was investigated by SEM microscopy and colorimetry. The hydrogels showed excellent cleaning properties and controlled water release, and they still performed satisfactorily after several cleaning uses. The obtained UV-hydrogels were compared to the well-known agar gels, showing benefits in terms of reducing excess water. This article shows that easy-to-make UV-cured hydrogels are an efficient tool for the cleaning of surface dirt from water-sensitive paintings, overcoming the limits of traditional cleaning methods.

Evaluation of solvent-based and UV-curing inkjet inks on the adhesion and printing quality of different aircraft surfaces coating

This work presents a study of digital inkjet printing technology for aerospace industry using different coatings on aluminum surfaces. The objective of this work is to understand the effect of some process parameters on digital inkjet printing technology in the aircraft industry for printing complex images, logos and other visual effects directly on the fuselage of aircraft with high quality, in order to replace conventional and manual aircraft painting processes. The consequent effects of the different coated surfaces on the properties of the printed images (e.g., adhesion, UV resistance, visual appearance and optical properties) were evaluated in order to understand how the coated surfaces affect these properties. For that purpose, solvent-based and UV-curing inkjet inks for industrial printing applications were used in the colors cyan, magenta, yellow and black on coated aerospace surfaces. The results show that the inkjet technology requires a white background substrate to match the conventional colors and there is an adhesion issue on conventional top coating used as a base for direct inkjet printing. The results reported here provide good evidence that the traditional aerospace surface used should be adjusted to improve the final print quality and paint film adhesion. The viscosity of UV-A inkjet ink is 2.1 times higher than UV-B ink and 2.4 times higher than solvent-based inkjet ink. The use of a new primer/top coating with clear coat is the optimal condition for maximizing the printed image properties, adhesion, UV degradation, low color variation (∆E*ab < 15) and improve the gloss effect (≥90GU). Although there are some challenges regarding this technology and these results create an effective strategy for the development of digital inkjet printing on aerospace surfaces with excellent final print quality.

The use of ground glass in red glazes: structural 3D imaging and mechanical behaviour using optical coherence tomography and nanoindentation

In this study we investigate the impact of the addition of colourless glass particles to red glazes, as seen in many 15th-17th-century easel paintings. With the use of reconstructions, we examined the influence of the paint preparation process on the morphological and mechanical properties of the paint film. Three sets of reconstructions were made, a control without ground glass, reconstructions with coarse or fine ground glass mixed in, and reconstructions where fine ground glass was ground jointly with the pigment oil mixture. The latter gave the desired consistency and colour based on visual inspection. The dried reconstructions were non-invasively imaged using optical coherence tomography (OCT). A data-analysis pipeline was developed for both the segmentation of the OCT images and the measurement of the size and spatial distributions of the glass particles within the glaze layer. Moreover, we used a nanoindentation protocol to measure the viscoelastic properties of the dried red glaze film. The OCT results show an expected decrease in median particle size with longer grinding-time, for which the additional grinding with pigment/oil resulted in a more narrow size distribution and a homogenous spatial distribution of the glass particles. The nanoindentation results indicate that the addition of glass particles increases the elastic and viscous moduli of the red glaze layers. The homogeneous size distribution, obtained by grinding the oil, pigment, and glass together, induces higher elastic and viscous moduli. Our imaging and analyses approach, combining OCT and nanoindentation, provides a non-invasive and quantitative investigation of glass particles in (semi-) transparent paint layers, and their effect on the mechanical properties of the glaze. The results of this study contribute to a better understanding of the artists’ addition of ground glass in paint layers.

Preparation of autoxidative water-reducible alkyd resins from waste polyethylene terephthalate.

In this paper, the waste polyethylene terephthalate (PET) was glycolysed by trimethylolpropane with zinc acetate as catalyst. The effects of different content glycolysis product of waste PET on the appearance, viscosity, particle size and molecular weight of autoxidative water-reducible alkyd resins and the corresponding film adhesion, flexibility, impact resistance, gloss, hardness and chemical resistance were studied. Meanwhile, experimental results were compared with commercial water-reducible alkyd and water-reducible alkyd without the glycolysis product of waste PET. The results show that the maximum concentration of PET in autoxidative water-reducible alkyd resins can reach 8.5 wt%, and the molecular weight, particle size and viscosity of water-reducible alkyd resin do not change much with the increase of PET concentration. The introduction of PET resulted in the viscosity of water-reducible alkyd resins being greater than that of water-reducible alkyd resin without PET; this is mainly because PET contains harder terephthalic acid monomer units. However, the particle size of water-reducible alkyd resins with waste PET is significantly lower than that of the water-reducible alkyd resin without PET; this is due to PET-free water-reducible alkyd resin containing more pentaerythritol with greater steric hindrance. In addition, the hardness of the water-reducible alkyd resin paint film (PET content is 8.5%) reaches 1H, which is higher than the hardness (HB) of the water-reducible alkyd resin paint film without PET and the commercial alkyd resin paint film, while the physical properties and chemical resistance of the former are comparable to those of the latter two kinds of paint films. Therefore, the use of waste PET in water-borne coatings systems not only reduces the cost of coatings, but also opens up a new market for recycled PET, which may contribute a promising method for management of waste PET.

A High-Temperature Digital Image Correlation Method and its Application on Strain Measurement of Film Cooling Holes

In this paper, a digital image correlation (DIC) method is developed and applied on film cooling holes in the submillimeter scale in high temperature. Compared with the traditional DIC method, the speckle patterning method and the optical system are improved. In detail, a kind of high temperature-resistant black paint is selected as the basecoat, and the white ZrO2 particles are evenly distributed on the specimen using high-pressure splashing method. Besides, to eliminate the radiation effect of the high-temperature specimen, the blue light source is used to illuminate the specimen, and the optical bandpass filter is placed in front of the camera to allow the blue light passing. In order to verify the DIC method, the strain measurement on a specimen with single skew hole is performed. The relative error in high temperature of the maximum strain between the measurement results and the numerical simulation results given by the finite element method (FEM) is 12%. The strain concentration factor of the single skew hole is measured as 1.83. Finally, the developed method is applied to the strain measurement of the structure with multiple film cooling holes in 870°C. The X-shape strain distribution can be observed at the hole with maximum stress, which suggests that the strain field of multiple holes has coupling effect. In addition, the strain concentration factor of multiple film cooling holes increases to 2.34.

Research of Turbine Oil Varnish in Generator Unit

In recent years, due to the fact that thermal power generating units have been deeply involved in the peak shaving work of the power grid, the frequent start and stop operations of the units and rapid load-carrying operations have made the operating conditions of the units very bad. In large-scale thermal power generation units, shutdown accidents caused by varnish failures are becoming more common. Take the serious varnish failure of Unit 3 in a domestic power plant as a case for analysis. The steam turbine oil after the varnish is formed is fully analyzed and tested and the metal ion content test is carried out. The changes in the physical indicators of the steam turbine oil during the formation of the varnish are studied to determine the influence of the steam turbine oil on the physical indicators of the steam turbine oil during the formation of the steam turbine oil. The operation and maintenance personnel can detect the varnish in advance through the daily sampling and analysis of the steam turbine oil, and timely take treatment measures to remove the varnish components in the oil to ensure the safe and stable operation of the unit. This article summarizes the reason for the formation of varnish and the detection method of varnish. It is of great significance to effectively discover and control the production of varnish during the operation of the generator set, to study the formation mechanism of varnish and to find an effective method to remove varnish. This article also introduces the commonly used paint film treatment methods for the convenience of electric power technicians.

Modulating Conductivity in Paintable Films from Solvent-Exfoliated Inks of 2D MoS2 and Bi2te3

Research on two-dimensional (2D) layered materials such as graphene,(1) transition metal dichalcogenides (TMDs), carbide and carbonitride relatives called MXenes,(2) has progressed beyond discovery to a wide range of uses. (3,4) In all applications where electronic transport is important, 2D materials, their assemblies, deposition, homo- and hetero-interfaces, layered networks, and composite with polymers, strongly influence the nature of conductivity and consequently the type of electrode or device. Photonics and optoelectronic investigations (5,6) are also sensitive to engineering of 2D materials and their composites, while energy storage and thermoelectric applications using 2D materials must take into account ion accessibility and thermal conductivity, respectively, in addition to electrical conductivity.Exfoliation of parent bulk crystals to give 2D and few-layer MoS2 (7,8) and Bi2Te3 dispersions in solvents may also be promising functional inks. Whether thixotropic or dilatant, inks from particle dispersions are the basis of many printing and coating technologies.(9,10) Incorporating new functionality using 2D materials with standard processing has potential for interesting applications.Here, we developed inks using high concentrations of exfoliated MoS2 and Bi2Te3 2D layer suspensions that can be painted as uniform films on substrates (11,12). Conductivity is controlled at material-level by high quality exfoliated 2D sheets, and in the case of Bi2Te3 we examined the influence of a PEG400 binder additive to the ink. We discuss the nature of in-plane electronic conductivity in painted films from both of these 2D material inks, and summarize measurements that show how conductivity is altered by the painting direction and aspect ratio of coated films. References (1) A. K. Geim, Science, 324, 1530 (2009).(2) B. Anasori, M. R. Lukatskaya, and Y. Gogotsi, Nat. Rev. Mater., 2, 16098(2017).(3) V. Nicolosi, M. Chhowalla, M. G. Kanatzidis, M. S. Strano, and J. N. Coleman, Science, 340, 1226419 (2013).(4) C. O’Dwyer, L. Walsh, F. Gity, S. Bhattacharjee, and P. K. Hurley, Electrochem. Soc. Interface, 27, 53 (2018).(5) L. Britnell et al., Science, 340, 1311 (2013).(6) F. Xia, H. Wang, D. Xiao, M. Dubey, and A. Ramasubramaniam, Nat. Photon., 8,899 (2014).(7) E. Carroll, D. Buckley, D. Mc Nulty, and C. O’Dwyer, ECS J. Solid State Sci. Technol. 9 093015 (2020).(8) V. Sánchez, E. Benavente, V. Lavayen, C. O’Dwyer, C. M. S. Torres, G. González, and M. A. S. Ana, Appl. Surf. Sci. 252, 7941 (2006).(9) E. B. Secor, B. Y. Ahn, T. Z. Gao, J. A. Lewis, and M. C. Hersam, Adv. Mater., 27,6683 (2015).(10) D. McManus et al., Nat. Nanotechnol., 12, 343 (2017).(11) E. Carroll, D. Buckley, V. Mogili, D. McNulty, M. S. Moreno, C. Glynn, G. Collins, J. D. Holmes, K. M. Razeeb, C. O’Dwyer, Chem. Mater. 29, 7390-7400 (2017).(12) E. Carroll, D. P. Buckley, G. Collins, J. D. Holmes, K. M. Razeeb, and C. O'Dwyer, ECS Trans. 64, 1 (2015).

Effect of Ag, Au, TiO2 metallic/metal oxide nanoparticles in double-slope solar stills via thermodynamic and environmental analysis

In recent years the use of nanoparticles in solar desalination is an emerging approach for improving the performance of systems. Utilizing nanoparticles in black paint of solar stills employed by some researchers but the number of studies in this context is limited. In all previous studies researchers usually utilized a single type of nanoparticle. In the present study silver (Ag), gold (Au), and titanium dioxide (TiO2) with 0.1 wt% of concentration were utilized in three double-slope solar stills. Performance of the systems from energetic, exergetic, economic, exergoeconomc, enviroeconomic, CO2 reduction, and energy matrices are examined. Findings revealed that the thermal efficiency of Ag-based solar still is calculated by about 33.68% which shows an improvement around 7.6%, 20.7%, 38.2% compared to Au, TiO2, and conventional system while overall exergy efficiency of Ag-based system with 2.34% is higher by about 7.3%, 32%, 70.5% in comparison with aforementioned systems respectively. The exergoeconomic results based on energy and exergy from highest to lowest were obtained by Ag, TiO2, conventional, and Au-based solar stills. Moreover, the economic assessment showed that the lowest and highest cost of distilled water with 0.0065 $/l.m−2 and 0.0289 $/l.m−2 were produced by Ag-based and Au-based solar stills. The rate of CO2 mitigation for the systems with Ag, Au, TiO2, and conventional was calculated by about 10.82, 10.02, 8.87, 7.7 t/y respectively. The energy payback time (EPBT) for all systems was less than 3 years. It can be concluded that using silver nanoparticle regarding the amount of improvement and the cost, is the most effective particle while the gold nanoparticle due to its high cost is not appropriate for use in solar stills.

Effect of Water-Based Emulsion Core Microcapsules on Aging Resistance and Self-Repairing Properties of Water-Based Coatings on Linden

The purpose of this paper was to discuss the best coating technology of water-based coatings containing microcapsules, and the anti-aging and self-repairing properties of water-based coatings containing microcapsules. Urea-formaldehyde encapsulated Nippon water-based emulsion microcapsules were prepared, and water-based coatings containing microcapsules were prepared. The optical and mechanical properties of the coatings under different coating technologies were investigated. Under the best coating technology, the aging resistance and self-repairing performance of the coating film were investigated. Experimental results showed that coating technology had no effect on color aberration of the coating film. The coating technology with two coats of primer, three coats of topcoat, addition of microcapsules into primer, had excellent glossiness, shock resistance of 12.0 kg·cm, adhesion of 0 grade, and fracture elongation of 26.3%. Compared with the coating film without microcapsules, the coating with microcapsules had better aging resistance and self-repairing property, and the self-repairing rate was about 20.0%. Compared with the paint film with Dulux water-based emulsion microcapsules, the paint film with Nippon water-based emulsion microcapsules had a higher self-repairing rate. This study provides a technical basis for self-repairing water-based coatings.

Photoacoustic characteristics of carbon-based infrared absorbers

We present an experimental comparison of photoacoustic responsivities of common highly absorbing carbon-based materials. The comparison was carried out with parameters relevant for photoacoustic power detectors and Fourier-transform infrared (FTIR) spectroscopy: we covered a broad wavelength range from the visible red to far infrared (633 nm to 25 μm) and the regime of low acoustic frequencies (< 1 kHz). The investigated materials include a candle soot-based coating, a black paint coating and two different carbon nanotube coatings. Of these, the low-cost soot absorber produced clearly the highest photoacoustic response over the entire measurement range.

Calcium antimonate: A new discovery in colour palette of Paestum wall paintings

During a restoration and diagnostic campaigns carried out on Paestum funerary slabs belonging to the Lucanian funerary art, calcium antimonate (CaSb2O6) was detected for the first time in the pictorial layers. This artificial pigment, widely employed as opacifier both in ancient glass and glaze covering clay objects, was found in the wall paintings, regardless of the colour, supporting the hypothesis of an intentional addition of calcium antimonate to the pigments and the involvement of ceramic painters.A multi-analytical approach was performed on 32 funerary slabs (6th – 3rd century BCE), currently located at the National Archaeological Museum of Paestum (Italy) using both polarized light microscopy and environmental scanning electron microscopy equipped with energy dispersive X-ray spectrometer, micro X-ray fluorescence, micro Raman spectroscopy, Fourier Transform Infrared spectroscopy and powder X-ray diffraction.The results confirmed the use of a limited number of pigments, usually applied with fresco technique, although in many cases the stratigraphy of the painted layer showed morphology of mezzo fresco technique, but no organic binders were found. The hues of vegetal decorations were obtained using green earth, sometimes Egyptian blue mixed with yellow ochre, carbon and bone blacks, and orpiment. The alteration of green earth and other iron-containing pigments are likely responsible for the discolouration of the original hues. In red paints, hematite and red ochre are frequently associated with ilmenite, a typical volcanic mineral. Egyptian blue was used in blue paints while in black paints it was mixed with carbon and bone black pigments.

Encapsulation by Directed PISA: RAFT‐Based Polymer‐Vesiculated Pigment for Opacity Enhancement in Paint Films

Front Cover: Article number 2100008 by Brian Hawkett and co-workers, a directed polymerization-induced self-assembly process is used to encapsulate titanium dioxide particles in the form of polymer vesiculated pigment to improve their light scattering efficiency in water-based paints. The improvement is attributed to well-distributed light scattering pigment centers in polymer films as depicted in the front cover.

Photocatalytic air purification: Effect of HNO3 accumulation on NOx and VOC removal

The effect of photocatalytically generated surface HNO3 on NOx and VOC removal activity is investigated using three very different photocatalytic films, namely, P25 TiO2, a commercial exterior paint (produced by STO Gmb) and a commercial air-purifying curtain fabric (IKEA). The paint required accelerated weathering and the cloth UV-preconditioning before exhibiting significant activity. When tested using the removal of nitric oxide ISO 22197-1:2016, the NO ISO, all films exhibited decreasing NOx removal activity and decreasing photocatalytic activity for NO removal with increasing irradiation time, so much so that both the STO paint and P25 films showed little NOx removal activity after the 5 h irradiation period. In all cases the loss in activity was attributed to the generation of a surface layer of HNO3, which was found to persist for at least 15 h and up to 7 days on a P25 film but could be readily rinsed away. The CaCO3 in the STO film, and the fibrous nature of the IKEA cloth appeared to largely eliminate the negative effect on NOx removal activity after 7 days. The activities exhibited by these films for the photocatalysed oxidation of acetaldehyde appeared unaffected by the presence of a photocatalytically generated HNO3 film. The relevance of the results to current, commercial photocatalytic products for air purification is discussed briefly.

Indoor and Outdoor Performance Study of Metallic Zinc Particles in Black Paint to Improve Solar Absorption for Solar Still Application

In this study, the effects of metallic zinc (Zn) particles were studied to increase surface temperature on a solar-still absorber, which is a major component of increased production. Various concentrations of Zn particles were mixed in black paint and applied to the absorber plate. SEM and XRD were used to examine and confirm the surface morphology and phase identification of as-received powder. UV-Vis spectroscopy was used to examine light-absorption properties. Finally, extensive indoor testing (using an improvised solar emulator) and outdoor testing were conducted to optimize the concentration. The specimens containing 10 wt% Zn in black paint showed the highest increase in temperature, i.e., 103.53 °C in indoor conditions at 1000 W/m2 irradiation, which is 59.17% higher than a bare aluminum plate and 17.57% higher than an only black-paint-coated aluminum plate. On the other hand, specimens containing 10 wt% Zn reached just 87.53 °C, compared to 80.00 °C for an only black-paint-coated aluminum plate and 60.62 °C for bare aluminum.

광주지역 산업폐수 업종별 TOC 배출 특성에 관한 연구

In this study, 182 industrial wastewater samples obtained from Gwangju were assigned to 16 industries to investigate the characteristics of organic indexes(TOC, NPOC, COD_Mn, and DOC). The average COD_Mn and TOC concentrations by industrial wastewater classification in Gwangju in descending order were as follows : other machinery and equipment manufacturing > painting and other film treatment > textile dyeing, cleaning, and finishing processing. The correlations between TOC and COD_Mn, NPOC, DOC showed high positive correlation coefficients which were more than 0.8. According to the revised Water Environment Conservation Act 2020 in which COD_Mn from wastewater discharge facilities was replaced with TOC, a COD_MN concentration of 130 mg/L in an “Na” region where the volume of wastewater discharge is lower than 2,000 m3/day, corresponds to 75 mg/L TOC, and the concentration ratio of COD_MN to TOC is 1.73. The average ratio of COD_Mn to TOC in five metropolitan cities (Gwang, Ulsan, Daejeon, Incheon, and Busan) was 1.55, and the converted TOC concentration corresponding to 130 mg/L COD_Mn was 84 mg/L. The average measurement ratio of COD_Mn to NPOC was 1.7, which was close to the COD_Mn to TOC ratio of 1.73. These results propose that TOC concentration in wastewater discharge from “Na” regions should be changed to 84 mg/L from the current 75 mg/L or TOC concentrations might be applicable to NPOC concentrations in all wastewater discharge facilities.

Characterization of retroreflective tape optical properties for use with position-sensitive scintillator detectors

Reflective materials such as Teflon and Enhanced Specular Reflector are commonly used to maximize light collection in scintillator-based radiation detection systems. While effective, in most cases, the spatial information carried by the light is diminished or lost entirely. Retroreflectors, in contrast, better preserve the spatial information and have been shown to improve the localization performance of such systems. In this work, the relative retroreflectivity of a selection of commercial retroreflective tapes and their performance impact when coupled to a plastic scintillator are reported. We demonstrate improved localization performance with some tapes compared to Teflon and black paint.

Flexible Daytime Radiative Cooling Enhanced by Enabling Three-Phase Composites with Scattering Interfaces between Silica Microspheres and Hierarchical Porous Coatings.

Daytime radiative cooling has attracted considerable attention recently due to its tremendous potential for passively exploiting the coldness of the universe as clean and renewable energy. Many advanced materials with novel photonic micro/nanostructures have already been developed to enable highly efficient daytime radiative coolers, among which the flexible hierarchical porous coatings (HPCs) are a more distinguished category. However, it is still hard to precisely control the size distribution of the randomized pores within the HPCs, usually resulting in a deficient solar reflection at the near-infrared optical regime under diverse fabrication conditions of the coatings. We report here a three-phase (i.e., air pore-phase, microsphere-phase, and polymer-phase) self-assembled hybrid porous composite coating, which dramatically increases the average solar reflectance and yields remarkable temperature drops of ∼10 and ∼ 30 °C compared to the ambient circumstance and black paint, respectively, according to the rooftop measurements. Mie theory and Monte Carlo simulations reveal the origin of the low reflectivity of as-prepared two-phase porous HPCs, and the optical cooling improvement of the three-phase porous composite coatings is attributed to the newly generated interfaces possessing the high scattering efficiency between the hierarchical pores and silica microspheres hybridized with appropriate mass fractions. As a result, the hybrid porous composite approach enhances the whole performance of the coatings, which provides a promising alternative to the flexible daytime radiative cooler.

Encapsulation by Directed PISA: RAFT-Based Polymer-Vesiculated Pigment for Opacity Enhancement in Paint Films.

A novel method is demonstrated to encapsulate titanium dioxide pigment using directed polymerization-induced self-assembly (PISA) with reversible addition-fragmentation chain-transfer (RAFT) controlled emulsion polymerization. The polymerization is carried out in a batch process in which both styrene (Sty) and the pigment are emulsified using triblock amphiphilic macro-RAFT copolymers as stabilizers. RAFT-controlled chain growth leads to directed lamellar self-assembly, forming polystyrene (PS) shells' encapsulating pigment particles with 100% efficiency. The pigment resides either at centers of single-void vesicles or within the interior of multivoid vesiculated particles. The presence of complex morphologies such as spherical particles, nanofibers, nanoplatelets, and polymer vesicles confirms the PISA pathway. The process is optimized to preferably produce polymer-vesiculated pigment for use as an enhanced opacifier in water-based paint.

A Thermoelectric Energy Harvester Based on Microstructured Quasicrystalline Solar Absorber.

As solar radiation is the most plentiful energy source on earth, thermoelectric energy harvesting emerges as an interesting solution for the Internet of Things (IoTs) in outdoor applications, particularly using semiconductor thermoelectric generators (TEGs) to power IoT devices. However, when a TEG is under solar radiation, the temperature gradient through TEG is minor, meaning that the TEG is useless. A method to keep a significant temperature gradient on a TEG is by using a solar absorber on one side for heating and a heat sink on the other side. In this paper, a compact TEG-based energy harvester that features a solar absorber based on a new class of solid matter, the so-called quasicrystal (QC), is presented. In addition, a water-cooled heat sink to improve the temperature gradient on the TEG is also proposed. The harvester is connected to a power management circuit that can provide an output voltage of 3 V and store up to 1.38 J in a supercapacitor per day. An experimental evaluation was carried out to compare the performance of the proposed QC-based harvester with another similar harvester but with a solar absorber based on conventional black paint. As a result, the QC-based harvester achieved 28.6% more efficient energy generation and achieved full charge of a supercapacitor around two hours earlier. At last, a study on how much the harvested energy can supply power to a sensor node for Smart agriculture during a day while considering a trade-off between the maximum number of measurements and the maximum number of transmission per day is presented.

Zinc sulfide pigments

Abstract Zinc sulfide pigments belong besides titanium dioxide and zinc oxide pigments to the most important inorganic whites. The pigments are mostly used in primers, plastics, fillers, putties, artists’ colors, and emulsion paints. Zinc sulfide pigments are divided into pure zinc sulfide (ZnS) and lithopone (mixtures of ZnS with BaSO4) pigments. They are synthesized using precipitation processes in aqueous medium. Compared with pure zinc sulfide pigments, lithopone pigments have a much larger technical importance.