Microstructural Analysis Protocol – Yongzheng Monochrome Matte Turquoise Glaze

Nona Dronova, D.Sc., ProfessorORCID: https://orcid.org/0009-0007-4867-9074 Abstract This study presents a comprehensive examination of two Yongzheng-period porcelain vases covered in a monochrome matte turquoise glaze, representing the imperial Ru-type revival tradition of the early 18th century. The analysis includes high-magnification optical microscopy, colorimetry with CIE LCh and HSV coordinates, and comparative study with museum-held Ru-type examples. The findings confirm that both vases share identical glaze formulation and chromatic characteristics, aligning with known imperial workshop practices under Superintendent Tang Ying. Keywords: Yongzheng, Ru-type, turquoise glaze, monochrome porcelain, Qing dynasty, colorimetry, microstructure, imperial porcelain 1. Introduction Monochrome glazes of the Yongzheng period (1723–1735) reflect a refined revival of classic Song-dynasty Ru ware aesthetics. The turquoise-blue matte glaze discussed here belongs to this revival, characterized by a delicate satin surface, subtle optical depth, and chromatic restraint. The two examined vases differ in form—a double-gourd and a pear-shaped vase with flared mouth—but exhibit identical glaze properties. 2. Materials and Methods Objects: Two porcelain vases, Yongzheng mark and period, monochrome matte turquoise glaze. Microscopy: High-resolution optical micrographs at various points on the glaze surface and impressed reign marks. Colorimetry: RGB values extracted from glaze-only pixel masks; conversion to HSV and CIE LCh coordinates. Comparative Research: Cross-referenced with collections of the National Palace Museum, Taipei; the Metropolitan Museum of Art, New York; the British Museum; and the Baur Foundation, Geneva. 3. Microstructural Analysis Crystalline Texture: Fine-grained microcrystalline matrix producing a diffuse, “snow-like” reflection. This is due to controlled crystallization in the Pb–Si glassy phase during cooling. Surface Gloss: Satin lustre, silk-like tactile feel; uniform light scattering without specular highlights. Chromatic Homogeneity: Even turquoise-blue tone, no pigment segregation or mottling. Interaction with Impressed Mark: Glaze flows evenly into incised seal strokes, preserving sharpness and avoiding pooling; optimal viscosity at firing temperature. Absence of Crackle: No visible crackle network; glaze is monolithic and stress-free. Optical Depth: Subtle depth effect from light scattering on microcrystals and the porcelain body interface. Object: Two Yongzheng-period porcelain vases with monochrome matte turquoise glaze (Ru-type revival).Method: Optical microscopy, high-magnification imaging of glaze surface and impressed mark. 3.1. Crystalline Texture Under magnification, the glaze reveals a fine-grained microcrystalline matrix, producing a diffuse “snow-like” reflection. This effect results from controlled crystallization within the Pb–Si glassy phase during cooling. 3.2. Surface Gloss The glaze exhibits a satin lustre rather than a high gloss, producing a silk-like tactile sensation. Light scattering is uniform, with no specular highlights except on microscopic protrusions. 3.3. Chromatic Homogeneity The turquoise-blue tone is evenly distributed, with no visible pigment segregation, mottling, or streaking. This indicates consistent pigment dispersion and firing stability. 3.4. Interaction with Impressed Mark Microscopy of the base seal mark shows that the glaze flows evenly into the incised strokes, maintaining sharp edges without pooling or excessive thickening. This is evidence of optimal glaze viscosity and controlled kiln temperature. 3.5. Absence of Crackle No crackle network is visible at high magnification; the glaze appears monolithic and free from stress-induced fissures, a hallmark of high-quality imperial wares. 3.6. Optical Depth The glaze layer demonstrates subtle optical depth, likely due to light scattering from embedded microcrystals and the underlying porcelain body. This contributes to the characteristic soft, velvety appearance. 4.Coloration & Color Coordinates Method. Color sampled instrumentally from glaze-only pixels (mask excluding background and seal recess). Two reporting swatches are provided: the objective measurement and an adjusted “daylight visual” for reader context. Swatches & coordinates (identical for both vases): Measured Standard: RGB (118, 146, 156); HSV H 195.8° / S 24.4% / V 61.2%; LCh L 58.8 / C 11.3 / h 228.7°. Daylight Visual (approx.): RGB (123, 170, 187); HSV H 195.9° / S 34.2% / V 73.3%; LCh L 66.9 / C 17.9 / h 230.2°. Equivalence of the two vases. Color difference between the two objects is within perceptual tolerance (visually indistinguishable in normal viewing); both present the same turquoise-blue hue (H ≈ 196–230° depending on model) with low-to-moderate chroma and satin reflectance. Visual descriptors. Matte/satin, silk-like surface; uniform coverage; no crackle; soft optical depth due to sub-micron scattering centers. Mechanism of Color (Ru-type revival) The observed turquoise-blue is consistent with a Ru-type revival glaze on porcelain under carefully controlled, slightly reducing conditions: Color genesis. A low-iron feldspathic glaze (Fe mostly as Fe²⁺) yields a bluish celadon tone. The hue direction toward blue (not green) is intensified by sub-micron bubbles and fine microcrystals that back-scatter short wavelengths, producing the characteristic soft, cool “sky-after-rain” appearance. Optical structure. The glaze shows a microcrystalline/snowy texture that diffuses specular light (satin gloss) and creates shallow optical depth—exactly what your micrographs illustrate. Processing. Thick, even application and high-fire maturation on a white porcelain body; the glaze flows cleanly around the impressed six-character seal with no pooling (optimal viscosity, steady kiln soak). The iron-washed footrim is another expected imperial workshop detail. Diagnostic outcome: Taken together—tone (LCh coordinates above), satin microcrystalline surface, reduction celadon optics, impressed under-glaze reign mark, and dressed foot—the glazes align with Yongzheng Ru-type (Song revival) monochromes, not with later low-fire copper–lead turquoise enamels. How to cite in the paper (ready-to-paste) Colorimetry statement.“Color of the matte turquoise glaze (both vases) measured from glaze-only masks: RGB 118/146/156; HSV H 195.8°, S 24.4%, V 61.2%; LCh L 58.8, C 11.3, h 228.7°. For reader visualization under diffuse daylight we provide an adjusted swatch, RGB 123/170/187 (HSV H 195.9°, S 34.2%, V 73.3%; LCh L 66.9, C 17.9, h 230.2°). The two vessels are chromatically equivalent within perceptual tolerance.” Ru-type mechanism note.“The turquoise-blue derives from a low-iron, reduction-fired feldspathic glaze exhibiting sub-micron bubble/crystal scattering (satin lustre). This Song-revival Ru-type formulation on porcelain was favored under Yongzheng; diagnostic workshop details include an iron-washed foot and an impressed six-character reign mark cleanly enveloped by the glaze.” Typological Context – Ru-type Revival under Yongzheng The turquoise-blue glaze corresponds to a Ru-type revival glaze on porcelain under slightly reducing conditions: Color Genesis: Low-iron feldspathic glaze (Fe mostly as Fe²⁺) yields bluish celadon tone, shifted toward blue by sub-micron bubbles and microcrystals that scatter short wavelengths. Optical Structure: Microcrystalline “snowy” texture diffuses light, creating the satin appearance. Workshop Details: Thick, even application; clean coverage of impressed seal; iron-washed unglazed foot typical of imperial Jingdezhen manufacture under Tang Ying. 5. Comparative Examples Museum Comparison — Baur Collection, Geneva This glaze closely corresponds to examples in the Baur Collection (Monochrome-Glazed Porcelain of the Qing Dynasty, Vol. 3), notably: Nos. A301, A316, A317 — dishes and bowls with lobed rims and identical pale turquoise glaze. The Baur catalogue notes that such glaze types trace their origins to early Ming and Liao technologies but achieve technical perfection under the Qianlong reign. Collector Alfred Baur (1865–1951) was among the first to systematically collect Qing monochrome glazes as a fully-fledged aesthetic category, rather than as utilitarian wares. In his inventory, such dishes are described as “soft turquoise glaze with satin finish”. Form and Function The lobed rim (moulded to simulate floral petals) derives from Song-dynasty ceramic traditions and was actively revived in the 18th century. This form was used for both monochrome-glazed wares and cobalt-decorated pieces, depending on intended use—ritual, tea service, or purely decorative. Typological Context — Ru-type Revival under Yongzheng (1723–1735) 1) Historical & workshop setting The Yongzheng court launched a program of reviving Song aesthetics, including Ru ware’s “heavenly blue” (tianqing) ideal. At Jingdezhen the initiative was run through the Imperial Household Department: Nian Xiyao served as superintendent, while Tang Ying was dispatched to Jingdezhen in 1728 as resident manager/assistant, working closely with potters and refining monochrome glazes for the throne. BrillВикипедия 2) What “Ru-type” means in Qing terms “Ru-type” in the 18th century denotes high-fired feldspathic celadon on a white porcelain body, engineered to evoke Northern Song Ru ware’s calm blue-green surface. Museum records for Yongzheng pieces describe: porcelain with celadon (Ru-type) glaze, slip or iron-wash on the footrim, and an underglaze cobalt seal mark—all imperial workshop hallmarks. asia.si.eduSong Ru itself is famed for a cool sky-blue glaze and refined forms; the Yongzheng “Ru-type” consciously imitates this look in porcelain rather than in the original stoneware body. theme.npm.edu.twChristie’s Materi