Overglaze Enamels Research Articles

Influence of viscosity and composition of alkali borosilicate lead-free frit on its reaction with hematite, and the color control of red overglaze enamels

Influence of viscosity and composition of alkali borosilicate lead-free frit on its reaction with hematite, and the color control of red overglaze enamels

High‐fired early English porcelains of the ‘A’‐marked group, east London (c. 1744): A Raman spectroscopy and electron microscopy compositional study

AbstractTwo rare, slip‐cast and highly translucent very early English manufactured porcelains, known as the ‘A’‐marked group, have been nondestructively analysed to determine their bulk composition, the mineralogy of their body, glaze and overglaze decorative enamels using Raman spectroscopy and electron microscopy. The bulk composition of the body and the glaze have been found to have a Ca‐Al‐Si composition and therefore demonstrate congruency with the specification of the Edward Heylyn and Thomas Frye patent of 1744. The patent specification required the porcelain paste to be prepared using unaker clay from the Carolinas and a lime‐alkali glass in varying proportions from 1:1 to 4:1, which when fired at temperatures now shown to range upwards of 1280°C vitrifies to form a refractory porcelain containing β‐wollastonite, the calcic plagioclase feldspar anorthite, diopside and mullite. The glaze used was similarly formulated but required lower levels of aluminous clay and a higher proportion of the glass flux to enable vitrification to occur at a lower melting temperature and therefore acting as an optical pyrometer. Crystallites of wollastonite, diopside and cassiterite were recorded in the glaze. Compositions of the blue, black, brown, gold, green, red and purple decorations applied as overglaze enamels have been determined. It is concluded that this porcelain group is attributed to Bow manufacture in East London c. 1744–1745.

Hematite crystal growth in high-temperature lead-free multicomponent alkali borosilicate glass frit for red overglaze enamels

To elucidate the crystal growth process of hematite in high-temperature lead-free multicomponent alkali borosilicate glass, which is essentially important to control the color of red overglaze enamels, frit and hematite mixture is heat-treated and subjected to microscopic observations. Hematite particles slightly grew due to sintering at low temperature. Once the glass matrix formed near the softening point of frit, hematite dissolved into glass fluid. Hematite crystal growth concomitantly ensued with decrease in the number of hematite particles via Ostwald ripening as the temperature increased. The grown particles exhibited an anisotropic morphology with straight outlines reflecting crystal planes, the morphology of which is completely different from those grown by sintering and particles prior to heating. These results suggest that comprehensive understanding of frit and hematite from the perspectives of glass science and chemistry as well as powder technology are important to truly control the color of red overglaze enamels.

Chemical reaction between lead-free multicomponent alkali borosilicate glass frit and hematite during heat treatment

A mixture of a lead-free multicomponent alkali borosilicate glass frit containing zinc ions and hematite was heat-treated under various conditions to elucidate the reaction between the two components, which is essentially important for controlling the color of red overglaze enamels. Above the glass transition temperature, the interaction between the frit fluid and hematite was evident, as the viscosity of the frit decreased. Moreover, hematite dissolved, the iron ions diffused into the glass matrix and they precipitated on residual hematite, resulting in enhanced crystal growth through Ostwald ripening. Concurrently, the iron and zinc ions reacted to form zinc ferrite. During cooling, the supersaturated iron ions were consumed for precipitation of hematite and zinc ferrite. Because frit and hematite dramatically react during heat treatment, conventional modification of hematite alone is insufficient. Development of the frit exhibiting low reactivity toward hematite through precise control of physical properties is a future challenging issue.

Drastic enhancement of mechanical strength and thermostability of bright yellowish-red hematite/alumina composites having a unique disk-like structure via silica coating

Surface coating is a key technique used to enhance various properties of functional inorganic materials. We adopted a silica-coating treatment for preparing bright yellowish-red pigments using hematite/alumina composites, which have a unique porous disk-like structure. This treatment enhanced color, mechanical strength, and thermostability. The porous disk-like structure comprising Al-substituted hematite particles and alumina nanoparticles, which is fragile to mechanical impact and/or high-temperature heating, was a key factor to obtain high chroma bright-red color in the present system. Silica-coated samples having various Si molar ratios [x=Si/(Fe + Al + Si)] were prepared, and mechanical-strength and thermostability tests were conducted. The mesopores generated by an assembly of hematite particles and alumina nanoparticles were gradually filled with amorphous silica, thus achieving significant enhancement in mechanical strength and thermostability in color. The composite pigment can be used as a colorant for red overglaze enamels for porcelain, and shows significant potential for various other industrial coloring applications.

Multinuclear core/shell hematite/glass particles for peeling-free red overglaze enamels on porcelain

For red overglaze enamel decoration, a type of colored ceramic coating for ceramics, a partial peeling might occur in mass-produced ceramic ware products. In this study, multinuclear core/shell hematite/glass composite particles, comprising a hematite core and a glass shell, where hematite particles are highly dispersed in a glass matrix, were developed to prepare a red coating material that could achieve a bright red-colored overglaze enamel without peeling. A peeling-free, bright yellowish red-colored overglaze enamel could be obtained when using the composite particles as the red paint. The former function (preventing peeling) can be derived from micrometric size of the shell glass particles and the latter function (high chroma and lightness) is caused by highly dispersive hematite particles in the shell glass particles. Our results suggest that the composite particles are suitable for mass-production due to their peeling-free nature, indicating a potential to be widely used as coloring for ceramic coating products.

Bright greenish-yellow pigments based on Sc2−xFexO3 solid solutions with bixbyite structure

An oxide system Sc2−xFexO3 prepared by a conventional solid-state reaction method was found to change its color from the well-known reddish color at x = 2.0 to a yellowish color at x ≈ 0.6 and to a greenish-yellow color at 0.2 ≤ x ≤ 0.4. According to the structural characterization results for this system, the monophasic corundum phase region persists for 1.6 ≤ x ≤ 2.0, whereas the bixbyite-type phase is monophasic for 0 ≤ x ≤ 1.0. The intermediate region of 1.2 ≤ x ≤ 1.4 is a mixed region. Because green is a rare color for iron oxides, powder of the most typical composition, x = 0.4, with (L*, a*, b*) coordinates of (77.3, −0.5, 51.0) was tested as a pigment for a Japanese-style painting and also as an overglaze enamel on porcelain; reasonably good results were obtained.

Non-invasive Raman identification of crystalline and glassy phases in a 1781 Sèvres Royal Factory soft paste porcelain plate

A Raman study of a Sèvres soft paste (frit) porcelain plate allowed the identification of both the crystalline and amorphous phases. Cristobalite and pseudowollastonite gave main Raman signatures in the body where also tridymite, amorphous alkali silicate glass and lead arsenate apatite were detected. Na0.4K0.1Ca0.5Pb4(AsO4)3 lacunar apatite is identified as opacifier in blue and green overglaze enamel. Pb-Sb-reach pyrochlore (Naples Yellow) pigment was found in yellow and green overglaze enamels. The orange hue is obtained by superposing a hematite bearing red paint stroke over the yellow. These results are compared to those previously obtained by detailed OM, SEM, XRD and XRF analyses. Some of the phases identified by XRD (quartz, tridymite) are hardly detected by Raman and vice versa cristobalite was not found by XRD, most probably due to its low amount.

Interaction between lead‐free multicomponent alkali borosilicate glass frits and hematite in red overglaze enamels

AbstractJapanese traditional red overglaze enamel decorations on porcelain known as akae are produced using lead‐containing frits, leading to a problem of lead release. Although many lead‐free frits have been developed, a well‐colored akae has not yet been realized, mainly because of no information on the reaction between lead‐free frits and hematite during the heating process in akae production. To reveal the effect of such interaction between the frits and hematite in akae on the color tone, various akae test pieces were prepared and investigated. On using low‐melting‐point lead‐free alkali borosilicate glass system, which contain zinc oxide, the formation of zinc ferrite proceeds simultaneously with the dissolution and particle growth of hematite in the frit melt. The particle growth rate due to dissolution and precipitation in the frit melt is faster than that due to sintering of particles caused by heat treatment of hematite powder in dry process. The dissolving capacity and promoting effect of particle growth depended on frit compositions. We also showed that the composition of akae glass layer varies because of ions diffusing from the glaze layer. Compositional changes in the akae glass could strongly affect the reactivity between the frits and hematite, resulting in variation in the color tone, the crystal phases formed, and their segregated states.

A polychrome Mukozuke (1624–1644) porcelain offers a new hypothesis on the introduction of European enameling technology in Japan

This study was carried out in an attempt to resolve the issue of the introduction of overglaze enameling in Japan through non-destructive analysis of the overglaze enamels that decorate the only known polychrome mukozuke dish (to be used in the tea ceremony) bearing the early Japanese date mark ‘Kan’ei Nen Sei’ (made in the Kan’ei period) (1624–1644). The investigation focused specifically on the overglaze yellow enamel and the underglaze blue pigment, for they could provide valuable information on the production workshop and geographical area of origin. Owing to the extraordinary importance and extreme rarity of this newly-discovered dish, it was mandatory not to sample it. Therefore, Energy-Dispersive X-Ray Fluorescence (ED-XRF) and Raman spectroscopy were used to obtain, in a non-destructive way, both elemental and molecular information about the coloring agent present in the yellow overglaze enamel. The underglaze-blue pigment at the base mark was also investigated. Besides a detailed literature research, a comparison was made with the chemical composition of fully identified and dated polychrome decorated Chinese and Japanese porcelains, and the results are reported in this work. The obtained analytical evidence has proved to be crucial in identifying the first use of Naples Yellow in Japan, and in resolving the issue of the origin of overglaze enameling, providing the missing step that actually led to the first development of the technique in Arita in the 1630s. Furthermore, it has shown that the Raman shift of the Pb mode of the A2O’ lattice is greatly affected by the firing temperature for enamel decoration, and that this specific characteristic of Naples Yellow, along with its elemental composition, can help determine its area of origin and period of manufacture.

Phase and compositional analysis of a Sèvres soft paste porcelain plate from 1781, with a review of early porcelain techniques

Optical microscopy, X-ray diffraction, X-ray fluorescence and scanning electron microscopy analyses were carried out on a typical Sevres soft (frit) porcelain plate from 1781 in order to determine the chemical and mineralogical composition as well as the microstructure of its ceramic body, glaze, overglaze decoration and gilding. The body is rich in SiO 2 (73 mass%), CaO (16) and alkali oxide (8) and shows acicular wollastonite and tridymite crystals embedded in a glassy matrix consisting of SiO 2 (75), K 2 O (12) and CaO (9). The 50–90 µm thick, transparent lead glaze (40.9 PbO) contains 47.6 SiO 2 , 6.5 K 2 O and 3.5 CaO and shows a 35–75 µm thick reaction zone (50 SiO 2 , 30 PbO, 14 CaO) towards the body. The maximum thickness of the different paints is 50 µm, with 15 µm as mean thickness of the individual paint stroke. Two blue colours, for the dentil comb and the flower painting, are chemically distinct (colouring CoO in the dental rim 7, in the flower’s blue 2 mass%) and contain many As- and Pb-rich globules and dendrites. Pseudohexagonal shaped platelets of Pb–Sb–Sn triple oxide crystals, embedded in a colourless glassy matrix, generate the opacity and the colour of the yellow paints. Opaque olive green colours are created by the combination of such yellow crystals with a bluish, Cu and Co bearing glassy matrix. The opaque red overglaze enamel is a mechanical mix of yellow Pb–Sb oxide crystals with an iron-rich (16 Fe 2 O 3 ) Pb–silica glass. Purple is very homogeneous and shows tiny drops of pure gold (max. diam. 0.5 µm) in a glassy matrix (47 PbO, 46 SiO 2 , 5 K 2 O). Violet is a mechanical blend of flower’s blue and purple. The pure (99.5 Au, 0.5 Fe 2 O 3 ) gilt consists of several folded gold particles. The results of this study are only broadly consistent with the archival documented 18 th century technologies. The compositional dissimilarities of the studied enamels suggest that each colour was independently fritted. Consequently, the original colour recipes written down by Hellot in 1753 must have been modified in the 30 years since then.

湿式合成法で作製したAl固溶ヘマタイト粒子の分散凝集状態が粉末と赤絵の色調に及ぼす影響

湿式合成法で作製したAl固溶ヘマタイト粒子の分散凝集状態が粉末と赤絵の色調に及ぼす影響

Well-Dispersed α-Fe2O3 Particles for Lead-Free Red Overglaze Enamels through Hydrothermal Treatment.

The traditional Japanese overglaze ceramic, akae porcelain, typically known for Kakiemon-style wares, has been prized around the world for over 400 years. The red color of akae porcelain provides an attractive contrast to white porcelain. In recent years, because the use of leaded frit in making akae has been restricted by law owing to the effects of lead on human health and the environment, lead-free glass frit mixtures for overglaze ceramic wares have been developed in various porcelain production areas throughout Japan. However, current lead-free frit for red overglaze enamels produces a color that is duller than that of conventional leaded frit. Therefore, the development of red pigments that are suitable for use with lead-free frit is strongly desired. In this study, we used a hydrothermal process to prepare nanosized iron oxide and oxyhydroxide powders, which showed good particle dispersion in molten lead-free frit. The precursor paste was prepared by reacting iron nitrate with ammonium hydrogen carbonate and heated in a sealed vessel at 80–150 °C. The sample powder prepared at 90 °C was almost monophasic α-Fe2O3 (hematite) and exhibited the brightest red color (highest L*, a*, and b* values). This powder featured primary particles of ∼15 nm in diameter that aggregated to form secondary spherical particles of ∼100 nm in diameter. This powder was mixed with lead-free frit and applied as a red paint to a porcelain test piece. The resultant akae showed a bright red color with high L*, a*, and b* values that exceeded the values of akae prepared using conventional hematite powder. Microscopic analysis revealed that the hematite particles were well dispersed in the resultant glass layer, indicating that the hematite powders have good dispersibility in molten frit.

Controlling the Color of Lead-Free Red Overglaze Enamels and a Process for Preparing High-Quality Red Paints.

Akae porcelain, an artistic Japanese traditional overglaze ceramic typically known for Kakiemon-style ware, has fascinated porcelain lovers around the world for over 400 years because of the graceful red color displayed by akae that matches so well with white porcelain bodies. In this work, we clarified the factors that control the color of akae and those that are conventionally controlled by artisans based on empirical experience. Inspired by a recent particle-design method, we also developed a practical facile process to prepare red paints that yields high-quality akae. Various akae samples were prepared from a combination of lead-free alkali borosilicate glass frits with different particle sizes and hematite powders with differing dispersibilities. Polarized light microscopy, scanning electron microscopy, and transmission electron microscopy analyses indicate that considering only the dispersibility of hematite powders is not sufficient, but the frit-particle size must be controlled to obtain high-quality akae with a high reflectance value for ≥580 nm visible light. In addition, we developed a process for preparing high-quality red paints that uses a large-particle frit powder and a strongly aggregated-hematite powder, both of which are easily obtainable. The red paint composed of frit, hematite, and the solvent is mixed until the paint is drying. By adding more solvent and repeating this process three times, we obtained high-quality akae with a higher reflectance value than for the akae prepared from a frit with submicron-sized particles and weakly aggregated-hematite powder. On the basis of transmission electron microscopic observations, we consider the red paint to consist of a core/shell-like composite structure of frit and hematite, forming a three-dimensional network in the akae glass layer. The good dispersibility of these particles leads to high-quality akae.

Preparation of yellowish-red Al-substituted α-Fe2O3 powders and their thermostability in color.

Inspired by the traditional Japanese pigment Fukiya bengala, nanocomposite materials were synthesized using a polymer complex method, comprising Al-substituted α-Fe2O3 (hematite) particles with diameters ranging from 40 to 100 nm and ultrafine Fe-substituted α-Al2O3 (corundum) particles smaller than 10 nm in diameter. The obtained powders exhibited a vivid yellowish-red color and high thermostability, making them attractive as potential overglaze enamels on porcelain. Quantitative color measurements revealed that, when heated to 700, 800, and 900 °C, samples displayed high lightness (L*) and color-opponent dimensions (a* and b*) at 10 mol % Al. For the same particle size samples, L*, a*, and b* values increased with the Al molar ratio, revealing that Al substitution in the hematite structure intrinsically enhances lightness and chroma in hematite color. These samples mostly retained their color upon reheating at 900 °C, indicating their high thermostability. This thermostability should originate from the Al substitution-induced enhancement in lightness and chroma in hematite color, which should counter color fading caused by particle growth. These composite materials are expected to find application in the porcelain industry, cosmetics, and nanotechnology.

X-ray fluorescence applied to overglaze enamel decoration on eighteenth- and nineteenth-century porcelain from central Europe

Technical and chronological aspects of overglaze enamel production at historic porcelain factories in central Europe are discussed based on studies of over 180 objects at various laboratories. Results of analyses on representative objects, carried out primarily with X-ray fluorescence spectroscopy, are presented. Examples of eighteenth- and nineteenth-century decoration by Meissen, Du Paquier, and Hausmaler painters are described in detail. The findings highlight established glaze formulation practices and enhance understanding of the dating of objects based on the detection of zinc in yellow, blue, and green glazes. This study is the first to provide extensive scientific evidence on the composition of nineteenth-century overglaze enamel colors. In particular, the research highlights the frequent co-occurrence of both eighteenth- and nineteenth-century enamel formulations on objects, underscoring the need to examine all overglaze enamel colorants on porcelains before attributing the decoration to a particular time period.

Preparation, microstructure, and color tone of microtubule material composed of hematite/amorphous-silicate nanocomposite from iron oxide of bacterial origin

By heating an amorphous iron oxide produced by Leptothrix ochracea, an iron-oxidizing bacterium species, at 600–1100 °C in air for 2 h, vivid red-colored powdered materials including α-Fe2O3 (hematite) and amorphous silicate with high thermostability were prepared which offer potential for use as overglaze enamels on porcelain. The precise color tone of the materials greatly depends on the heat-treatment temperature. The most strikingly beautiful sample, heat-treated at 800 °C, is light yellowish-red in color (L* = 47.3, a* = 34.1, and b* = 34.6), has a unique microstructure, and does not fade in color even with reheating at 800 °C, which is the firing temperature for overglaze enamel on porcelain. The sample primarily consists of crystalline hematite particles ∼40 nm in diameter with slightly longer axis unit-cell parameters than those of pure hematite. The particles are covered with amorphous silicate phase ∼5 nm in thickness and are intricately interconnected into microtubules with an average diameter of 1.26 μm. The attractive color of this material is due to the following structural features: small particle size (∼40 nm), nanocomposite of hematite and amorphous silicate, and a microtubule structure that inhibits aggregation of individual hematite particles and microtubules.

CHARACTERIZATION OF 18TH‐CENTURY MEISSEN PORCELAIN USING SEM–EDS*

Analytical investigations of fragmented Meissen porcelains well dated to between 1725 and 1763 have been carried out using SEM–EDS. The aim of the analysis was to characterize elements in bodies, glazes and overglaze enamels in order to create a baseline data set of materials used in the manufacture of porcelain at the Meissen factory, Saxony, during the 18th century. Analyses indicate body and glaze compositions to be consistent with a post c.1720–30 date, when a change from a lime‐rich flux to a potassium‐rich flux is documented to have occurred. Overglaze enamel compositions are shown to be consistent with contemporary accounts of enamel preparations at Meissen. Overglaze enamel compositions show that mixtures of pigments, in addition to documented enamel 18th‐century preparations, were in use at Meissen between c. 1725 and 1763.

Analysis of CizhouMonochrome Green Enamels and Lead Glazes From Guantai Kiln in Northern China, Song to Jin Dynasty

ABSTRACTThe composition and microstructure of Cizhou monochrome overglaze enamels, the first known form of overglazed enamels in China, and green lead glazes from Guantai kiln were determined. Although microstructure and thickness of the enamels were very similar to those found for the single layer lead glazes, lead contents were lower. Enamels from the later part of the twelfth century formed a narrower compositional grouping than the lead glazes, indicating that increased control of the technology was attained. The monochrome enamels are thicker and have a composition distinct from that published for later painted enamels from sites other than Guantai. Increased viscosity and decreased values of thermal expansion coefficients were calculated for Guantai enamels relative to the glazes. An attempt to promote adhesion and reduce crawling may have caused the use of lower lead in the enamels relative to the single layer lead glazes.