Author: Nona D. Dronova, D.Sc., Professor

Abstract

This study presents an in-depth examination of a monochrome Chinese porcelain vase with an experimental speckled glaze commissioned by the Yongzheng Emperor (1723–1735), produced at the Imperial Kilns of Jingdezhen (景德镇官窑). The glaze, known in contemporary Chinese terminology as 仿古玉釉 (“imitation of ancient jade glaze”) and referred to in Western literature as quail-egg glaze, represents one of the rare and innovative surface treatments developed during this period.

Through macroscopic and microscopic analysis, including high-magnification imaging of the base mark, the widest section of the body, and the unglazed footrim, the research reconstructs the likely technological process used to achieve the distinctive “quail-egg” speckled effect. The findings highlight the exceptional level of craftsmanship in Imperial Jingdezhen production under Yongzheng’s reign, where glaze chemistry and firing techniques were manipulated to imitate the mineral inclusions and textural depth of ancient jade artefacts.

The vase’s technical, morphological, and artistic attributes support its attribution to the early 18th-century Imperial workshops and its classification as a significant example of Yongzheng-period experimentation in monochrome glazes.

Quail-Egg Glaze Vase (仿古玉釉)

Expert Catalogue Entry and Technological Analysis

1. Introduction

The reign of the Yongzheng Emperor (1723–1735) marked a pivotal period in the history of Chinese porcelain, characterised by deliberate experiments with colour, texture, and glaze technology. It is well-documented that the emperor himself, possessing refined artistic taste and a deep appreciation for the aesthetics of antiquity, personally commissioned the Imperial Kilns at Jingdezhen (景德镇官窑) to develop new glaze formulas imitating natural materials such as jade, agate, chalcedony, malachite, coral, and bronze.

In the Qing Gong Dang’an (Qing Dynasty Court Archives), written orders have been preserved in which the emperor demanded that craftsmen reproduce the “breath of antiquity” in contemporary vessels—making new vases appear as if they were artefacts that had endured the passage of centuries. From these directives emerged rare glazes such as 仿古玉釉 (imitation of ancient jade), 茶叶末釉 (tea-dust glaze), 郎窑红 (Lang red), as well as experimental speckled finishes referred to in Western literature as spotted glaze or quail-egg glaze.

The vase with quail-egg glaze presented here is a striking example of these experiments: it combines a refined monochrome base with a complex reactive surface pattern, creating the illusion of natural stone texture.

2. Reconstruction of Glaze Technology

Based on microscopic analysis of the provided fragments and technical descriptions of Yongzheng-period glazes, the following reconstruction of the glaze manufacturing process is proposed:

2.1. Porcelain body

• Material — fine white porcelain composed of kaolin, feldspar, and quartz.

• Preparation — wheel-throwing, light surface trimming, and preliminary drying.

2.2. Base glaze (background)

• Composition — high-fired lead–lime silicate glaze with minimal pigment content.

• Colour — greyish-white with a beige undertone.

• Firing — first high-temperature firing in an oxidising atmosphere at 1250–1280 °C.

2.3. Decorative pigmentation (spots)

• Pigments — iron oxides (Fe₂O₃) with possible addition of manganese dioxide (MnO₂) for a purplish hue and traces of copper oxide (CuO) for warm tonal shifts.

• Application method:

  • fine spraying of pigment solution through a sieve, or

  • droplet application using a brush with diluted pigment suspension, allowing the drop to spread on the surface, forming a halo.

2.4. Concentric spreading effect

• Occurs when the pigmented drop comes into contact with a still-wet glaze layer.

• Due to differences in surface tension and density, components separate into concentric zones: dark centre — lighter halo — semi-transparent edge.

2.5. Second firing

• Temperature — 1180–1200 °C (slightly lower to preserve the spot definition).

• Atmosphere — variable, with short reducing phases producing a rich range of brown-to-violet tones.

2.6. Final finishing

• Inspection for uniform gloss.

• Retouching of the base mark if partially covered by glaze, or cleaning the unglazed footrim.

📌 Key technological feature — imitation of natural mineral inclusions in stone (nephrite spotting). This was achieved using a reactive pigment mixture capable of colour shifts depending on micro-atmospheric conditions during firing. This explains the complex palette—from near-black centres to pale yellow halos—visible under magnification.

3. Microscopic Analysis

3.1. Micro-analysis of the base mark

• Coverage — the glaze fully coats the impressed seal mark, preserving crisp line definition.

• Gloss and smoothness — mirror-like surface without orange peel texture or bubble breaks, indicating high-temperature self-levelling of the melt.

• Colour variation — darker tone in the recesses of the mark due to local pigment concentration and light–shadow interplay.

• Technological note — the mark was applied before glazing, typical of genuine imperial wares from the Yongzheng period.

3.2. Micro-analysis of glaze at the widest part of the vase

• Spot morphology — three-zone structure (dark core — brown halo — light fringe) indicative of Fe²⁺/Fe³⁺ phase transitions under variable firing atmospheres.

• Transitional zones — soft gradient between background and spots, with a visible “coffee-ring effect” at the drop periphery.

• Phase separation — presence of microcrystals along phase boundaries (exsolution) in the glassy matrix.

• Glaze flow behaviour — fine, unbroken flow striations confirm optimal melt viscosity and precise firing control.

• Absence of defects — no micro-pits, bubble breaks, or devitrified matte areas.

4. Attribution and Significance

This vase represents a rare example of imperial monochrome 仿古玉釉 with the quail-egg effect, produced at the Jingdezhen Imperial Kilns during the Yongzheng reign. The combination of technological, morphological, and artistic features confirms both authenticity and the exceptional quality of the piece.

5. Catalogue Number

YZ-QUAIL-EGG-VS-026-CN

6. References

1. Tsao Ching-jih. Chronicles of Ceramic Industry.

2. The Complete Treasures of the Palace Museum: Monochrome Porcelain.

3. Pierson, Stacey. Imperial Chinese Ceramics. London, 2009.

4. Valenstein, S. A Handbook of Chinese Ceramics. Metropolitan Museum of Art, New York.

5. Dronova, N. D. What You Need to Know About Antique Chinese Porcelain [Что надо знать о старинном китайском фарфоре]. Moscow: OOO “Tipografiya KEM”, 2016, p. 238. DOI: 10.5281/zenodo.16794377. ISBN 978-5-9908782-6-6.