Copper-Red Peachbloom Glaze of the Kangxi Period: Green Moss-Like Flecks and X-Ray Fluorescence Analysis of a Scholar's Brush Washer

Object: Chinese porcelain brush washer, attributed to the Kangxi period (1662–1722), Qing dynasty. Abstract This study presents a non-destructive elemental investigation of a small Chinese porcelain brush washer associated with the scholar’s desk tradition and attributed to the Kangxi period (1662–1722). Particular attention is given to its copper-red peachbloom glaze (豇豆红, jiangdouhong), characterized by red areas, greenish transitions, and distinctive moss-like or lichen-like flecks. Portable X-ray fluorescence spectroscopy (pXRF) was employed to examine a red decorative area and the base of the vessel. The red area exhibited a copper concentration of 7,360 ppm, compared with 585 ppm in the analyzed base area, corresponding to approximately 12.6-fold copper enrichment. The red area also contained sulfur (2,550 ppm), arsenic (60 ppm), and tin (153 ppm). These findings are discussed in relation to published investigations of historical Chinese copper-red glazes, particularly the study by Sun Jing and colleagues (1991) on the coloration mechanisms of peachbloom glaze and a 2025 investigation of copper-red pigment recipes published in the Journal of the European Ceramic Society. The results demonstrate a pronounced elemental heterogeneity between the decorative red surface and the base. The observed enrichment in copper provides an experimental basis for examining the relationship between copper-bearing glaze technology and the characteristic red-green visual effects of Kangxi-period peachbloom porcelain. Keywords: Kangxi period; peachbloom glaze; jiangdouhong; copper-red glaze; underglaze copper; green moss-like flecks; scholar’s brush washer; portable X-ray fluorescence; Chinese porcelain; archaeometry. 1. Introduction The Kangxi reign (1662–1722) represents a significant period in the technological and artistic development of Chinese porcelain. During this era, the imperial kilns at Jingdezhen achieved remarkable refinement in the production of high-fired copper-red glazes. Among the most distinctive varieties is peachbloom, known in Chinese as 豇豆红 (jiangdouhong), a glaze celebrated for its subtle pinkish-red coloration, deeper crimson areas, greenish transitions, and small moss-like spots. These visual characteristics are especially associated with small porcelain objects intended for the scholar’s desk, including water vessels, brush washers, and other implements used in calligraphy and painting. The Metropolitan Museum of Art preserves several Kangxi-period brush washers decorated with peachbloom glaze. One example, accession number 29.100.352, exhibits the characteristic combination of reddish and greenish surface effects. The coexistence of red and green coloration is therefore a documented feature of this historical ceramic tradition. The present study examines the elemental composition of a small brush washer displaying comparable visual characteristics. The investigation focuses on the relationship between copper concentration, red coloration, and the formation of green moss-like or lichen-like flecks. 2. Description of the Object The investigated object is a small Chinese porcelain brush washer associated with the material culture of the scholar’s desk and attributed to the Kangxi period. Its decorative surface displays several characteristic features: Pinkish-red and deeper copper-red areas. Greenish transitions between the red regions. Irregular green spots resembling moss or lichen. A grey base exhibiting a network of glaze crackles. The combination of red and green areas within a single decorative system is particularly significant. In Chinese ceramic literature, the green formations characteristic of peachbloom glaze are described as 绿苔点 (lütaidian), literally “green moss-like spots.” These features are central to the technological interpretation of the vessel. Figure 1. General view of the Kangxi-period brush washer. [Author’s photograph to be inserted.] Figure 2. Copper-red surface with green moss-like flecks and transitional areas. [Author’s macrophotograph to be inserted.] Figure 3. Grey base showing glaze crackling. [Author’s photograph to be inserted.] 3. Analytical Methodology The elemental composition of the vessel was investigated using portable X-ray fluorescence spectroscopy (pXRF), a non-destructive analytical technique. The measurements were recorded in analytical report No. 940487, dated 28 October 2026. Instrumental parameters: Analytical mode: Geochem (3-Beam) Extra. Acquisition time: 45 seconds per measurement. Sampling procedure: in situ, non-destructive. Measurement No. 19: red decorative area (miska kras). Measurement No. 20: base of the vessel (miska niz). Elemental concentrations are reported according to the instrument output, using parts per million (ppm) and percentages. The measurements represent the elemental response of the analyzed surface regions under the specified instrumental conditions. 4. Experimental Results 4.1. Elemental Composition Table 1. Comparative pXRF results for the red decorative area and the base of the brush washer Element Red area, No. 19 Base, No. 20 Cu (ppm) 7,360 585 Fe (ppm) 8,270 4,200 S (ppm) 2,550 4,640 As (ppm) 60 ND, <8 Sn (ppm) 153 62 Pb (ppm) 11 21 Ca (%) 11.21 2.897 K (%) 1.569 3.318 Si (%) 27.93 33.91 Al (%) 7.04 5.81 Mn (ppm) 414 697 Zn (ppm) 77 172 ND = not detected above the reported instrumental detection threshold. 4.2. Copper Enrichment in the Red Area The most significant analytical observation is the pronounced copper enrichment of the red decorative region. The measured copper concentrations are: Red decorative area: 7,360 ppm (0.736%). Base: 585 ppm (0.0585%). The concentration ratio is: 7,360 / 585 = 12.58. Thus, the red decorative area exhibits approximately 12.6 times the copper concentration recorded at the base. This substantial difference demonstrates a localized enrichment of copper in the red decorative region. The result establishes a direct analytical relationship between the visually red area and elevated copper content, consistent with the use of copper-bearing materials in historical red-glaze technology. 4.3. Associated Elements In addition to copper, the red decorative area contains sulfur, arsenic, and tin. The principal concentrations are: Copper (Cu): 7,360 ppm. Sulfur (S): 2,550 ppm. Arsenic (As): 60 ppm. Tin (Sn): 153 ppm. The presence of these elements is particularly relevant to studies of historical Chinese copper-red pigments and glazes, in which copper-bearing particles associated with sulfur and arsenic have been investigated. Another notable feature is the calcium concentration of 11.21% in the red area, compared with 2.897% at the base. The differences in calcium, potassium, silicon, and aluminum reflect compositional heterogeneity between the investigated ceramic surfaces. 5. Coloration Mechanisms of Red and Green Peachbloom Areas 5.1. The Study by Sun Jing and Colleagues (1991) A particularly relevant scientific publication is the Chinese study: Sun Jing, Chen Xianqiu, Ruan Meiling, and Zhao Dafeng. 桃花片铜红釉的着色机理 (Coloration Mechanism of Peachbloom Copper-Red Glaze). Journal of the Chinese Ceramic Society, 1991, No. 6, pp. 549–555. The authors investigated three characteristic regions of peachbloom glaze: Red areas. Green moss-like spots. Red areas exhibiting greenish coloration. Their investigation identified distinct mechanisms associated with the different visual regions. The red coloration was attributed to finely dispersed metallic copper particles smaller than 2 μm. The green moss-like spots were associated with localized enrichment of Cu²⁺ ions within the glassy glaze matrix. Greenish transitional regions were associated with numerous microscopic particles containing copper sulfide. These findings are highly relevant to the interpretation of the investigated brush washer. Its visual structure — comprising red fields, green transitions, and moss-like flecks — corresponds to the principal color regions examined in the 1991 study. The publication therefore provides a scientific framework for understanding the complex red-green appearance of historical peachbloom glazes. 5.2. Copper and Reduction Firing The development of copper-red coloration in high-fired ceramic glazes is closely associated with oxidation-reduction processes during firing. Under reducing conditions, copper can form metallic particles that contribute to red coloration. Local differences in copper oxidation state, particle distribution, and the surrounding glassy matrix can produce variations in color. The resulting decorative surface may contain red, pink, and green regions within a single glaze system. In peachbloom technology, the distribution of copper through the glaze thickness is also important. Historical examples may exhibit a complex multilayer arrangement involving transparent glaze and copper-bearing material. The final visual effect develops through interactions among glaze composition, firing atmosphere, temperature, and copper distribution. 6. Comparison with Historical Copper-Red Pigment Research A recent study published in the Journal of the European Ceramic Society provides an additional technological context: A New Interpretation on the Recipe and Technological Origin of 14–18th Century Chinese Copper Red Paint. DOI: 10.1016/j.jeurceramsoc.2025.117535. The researchers examined 27 historical Chinese ceramic samples containing underglaze copper-red decoration and selected copper-red glaze materials. The analytical methods included scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), electron probe microanalysis with wavelength-dispersive spectroscopy (EPMA-WDS), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The study identified copper-bearing microphases involving sul