How Is Authentic Ru Porcelain Made?

"Seventy-two hands touch a single piece before it becomes porcelain" — this ancient Chinese proverb perfectly captures the extraordinary craftsmanship behind authentic Ru Porcelain, the crown jewel of China’s Five Great Kilns. While the full process includes over 100 micro-steps, the 28 critical stages below break down how ordinary clay from Ruzhou, Henan Province, is transformed into the legendary "rain-after-sky" celadon—once reserved exclusively for emperors.

Phase 1: Clay Preparation (Steps 1–10) – The Soul of Ru Porcelain

The unique jade-like texture and sky-blue hue of Ru Porcelain begin with its clay, sourced only from the mineral-rich mountains of Ruzhou. No other region in the world produces clay with the exact mineral composition needed for true Ru ware.

1.       Quarrying & Ore Selection: Master craftsmen hand-pick high-quality kaolin, quartz, and feldspar from local mines. They reject any stone with iron impurities, as these would discolor the final glaze.

2.       Natural Weathering: Raw materials are left outdoors for 4 to 6 months, exposed to sun, rain, and frost. This breaks down their crystalline structure and softens the clay.

3.       Manual Sorting: Each stone is inspected and sorted by color and texture individually, ensuring only the purest materials move forward in production.

4.       Stone Mill Grinding: Stones are crushed into small pieces and ground into fine powder using electric mills .

5.       Washing & Purification: The powder is mixed with spring water and washed repeatedly to remove remaining iron and heavy metals.

6.       Sedimentation: The clay slurry settles in large concrete pools for 6 to 9 months. Heavier particles sink to the bottom, while fine clay particles float to the top—ensuring a smooth, pure base.

7.       Filter Pressing: Hydraulic presses remove excess water, resulting in dense clay cakes with a precise 25% moisture content.

8.       Vacuum Pugging: Clay cakes are fed through a vacuum pug mill to remove 99% of air bubbles. These bubbles would cause cracking during firing.

9.       Hand Kneading: Each piece of clay is kneaded for 15 to 20 minutes. This further eliminates air pockets and aligns the clay particles for consistency.

10.    Aging (Chen Fu): The clay is wrapped in plastic and stored in a cool, dark place for 6 to 12 months to mature. This makes it more malleable and less likely to warp during shaping.

Phase 2: Shaping the Form (Steps 11–16) – Artisan Skill in Every Curve

This phase highlights the artisan’s decades of experience. Even with modern tools, premium Ru Porcelain pieces are still 100% hand-thrown to achieve perfect balance and symmetry.

11.       Design & Modeling: Master designers create original sketches and carve clay prototypes, drawing inspiration from the elegant aesthetics of China’s Song Dynasty (960–1279).

12.       Plaster Mold Making: Molds are created from prototypes for consistent production of popular shapes. Limited-edition pieces, however, remain entirely hand-thrown.

13.       Hand Throwing: The clay is centered on a spinning potter’s wheel. The artisan uses their hands to pull and shape it into the desired form—a skill that requires at least 10 years of practice to master.

14.       Trimming & Footing: Once the clay dries to a "leather-hard" consistency, excess material is trimmed away. The delicate foot ring is then carved—a step so important that a Chinese saying notes, "Three parts throwing, seven parts trimming."

15.       Hand Carving: Intricate patterns are carved into the surface using sharp bamboo tools. These subtle textures will become visible through the translucent glaze.

16.       Slow Air Drying: The unfired clay (called greenware) dries slowly in a shaded, well-ventilated area for 7 to 14 days. Rushing this step causes irreversible cracking.

Phase 3: Bisque Firing (Steps 17–19) – Transforming Clay to Ceramic

The first firing turns fragile wet clay into durable bisque ware, which is ready to absorb the famous Ru glaze.

17.       Low-Temperature Bisque Firing: Dried greenware is loaded into kilns and fired at 800–900°C (1472–1652°F) for 8 to 10 hours. This removes all remaining moisture and organic matter.

18.       Bisque Polishing: After cooling, each piece is hand-sanded with fine sandpaper to create a perfectly smooth surface—critical for an even glaze application.

19.       Rigorous Bisque Inspection: Every piece is inspected under bright LED light. Any with cracks, warping, or surface imperfections are discarded immediately.

Phase 4: The Secret Agate Glaze (Steps 20–24) – The Heart of Ru Porcelain

Ru Porcelain’s famous sky-blue glaze is its most closely guarded secret. Its core ingredient is agate—a precious stone that gives the glaze its distinctive jade-like luster and depth.

20.       Agate & Mineral Preparation: High-quality agate and other rare minerals are collected, sorted, and ground into an extremely fine powder—finer than flour.

21.       Glaze Formulation: The agate powder is mixed with feldspar, quartz, limestone, and other ingredients. The exact recipe is a closely guarded secret, passed down through generations of Ruzhou artisans.

22.       Glaze Slurry Making: Dry ingredients are mixed with spring water and stirred continuously for 4 to 6 hours to create a smooth, uniform glaze slurry.

23.       Dip Glazing: The bisque ware is dipped into the glaze slurry for exactly 2 to 3 seconds, ensuring an even coating 0.5–1mm thick. Premium pieces receive 2 to 3 coats for a richer finish.

24.       Glaze Trimming & Drying: Excess glaze is carefully wiped from the foot ring to prevent sticking during firing. The glazed pieces then dry completely for 24 hours before the final firing.

Phase 5: The Final Firing (Steps 25–28) – Where Magic Happens

This is the most critical and unpredictable stage. Even with perfect preparation, only 20–30% of pieces emerge as first-grade Ru Porcelain.

25.       Sagger Loading with Sesame Seed Nails: Each piece is placed in a protective clay sagger (container) to shield it from direct flames and ash. It is supported by 3 to 5 tiny "sesame seed" nails—leaving only small marks on the bottom, a signature of authentic Ru Porcelain.

26.       High-Temperature Reducing Firing: Saggers are stacked in the kiln, which is heated to 1280–1320°C (2336–2378°F) over 12 to 15 hours. The final 2 to 3 hours are fired in a reducing atmosphere (low oxygen), which converts iron oxides in the glaze to the famous sky-blue color.

27.       Slow Natural Cooling & Crackle Formation: The kiln is sealed and allowed to cool slowly over 3 to 5 days. As the temperature drops, the glaze contracts faster than the clay body, creating delicate crackle patterns—each unique to the piece. Contrary to common belief, these crackles are not defects but the most prized characteristic of genuine Ru ware.

28.       Final Inspection & Grading: The kiln is opened, and every piece is examined by master craftsmen. Only those with perfect glaze color, no defects, and beautiful crackle patterns pass. All imperfect pieces are smashed to prevent them from entering the market—upholding the legacy of Ru Porcelain’s quality.