The Making Process of Liuli (Chinese Colored Glaze)
Liuli, also known as Chinese colored glaze, is a precious traditional Chinese craft with a history of thousands of years. Listed as a national intangible cultural heritage in 2008, its making process is intricate and elaborate, requiring strict control of every step from raw material selection to final polishing. Each piece of Liuli is a combination of manual craftsmanship and natural fusion, taking more than ten days and dozens of procedures to complete. The following details the complete traditional making process of Liuli, showing the wisdom and patience of ancient and modern craftsmen.
1. Raw Material Selection and Preparation: The Foundation of Exquisite Liuli
The quality of Liuli depends first on the selection and preparation of raw materials, which is the premise of ensuring its luster, hardness and color. The main raw materials of traditional Liuli include ganzi soil (a high-quality soil for firing Liuli and porcelain in northern China), quartz sand, feldspar, lead ore, barium ore, and metal oxides for coloring. Among them, ganzi soil is particularly critical—it is usually mined from specific mountainous areas, and only the one with low iron content is selected, because high iron content will make the blank turn red and affect the brightness of the glaze color.
After selection, the raw materials go through several preparation steps. First, the ganzi soil is dried to remove moisture, making it easier to crush and grind. Then, it is mixed with auxiliary materials such as pyrophyllite and cooked tiles (accounting for about 15% of the proportion) to improve the anti-deformation ability of the product during production. Next, the mixed raw materials are crushed into powder as fine as flour, then put into large pools, soaked in water for 7 to 8 days for washing (also called yinni), and finally stirred and kneaded repeatedly—traditionally by stamping with feet or beating with mud forks at least three times—to make the mud uniform and tough, laying a solid foundation for the subsequent molding.
2. Mold Making: Carving the Blueprint of Liuli
Mold making is a key link that determines the shape and detail of Liuli, and it is mainly divided into two common methods: mold forming for daily and architectural Liuli, and lost-wax casting (Pate-de-verre) for exquisite artworks. For mold forming, craftsmen first design the shape and pattern, then carve the mold with wood or stone, and polish the inner surface to ensure that the blank can be smoothly demolded and the details are clear.
Lost-wax casting, the most difficult and delicate method, is often used for complex and exquisite Liuli works. First, craftsmen sculpt the original model, then coat it with silica gel layer by layer to make a negative mold. After the silica gel solidifies (taking 2 to 24 hours depending on the size of the work), the original model is taken out, and melted wax is poured into the negative mold to make a wax model identical to the original design. The wax model is then carefully trimmed to repair burrs and pores, and then coated with refractory gypsum to make a gypsum mold. Finally, the gypsum mold is placed in a steam bucket to melt and drain the wax, forming a hollow mold that can be used for casting—this step is called "dewaxing" and accounts for 30% of the entire process.
3. Blank Forming and Drying: Shaping the Initial Form
For Liuli made by mold forming, the refined mud is pressed or poured into the mold, and then carefully demolded after it takes shape to get the initial blank. For architectural Liuli such as glazed tiles, this step is also called "wenzuo", which focuses on ensuring the standardization and integrity of the blank shape. After forming, the blank must be dried naturally in a cool and ventilated place, and the drying speed must be controlled to avoid cracks caused by uneven heating and cooling. The drying time varies according to the size of the blank, usually taking several days to more than a week, until the moisture content of the blank is completely reduced to a safe range.
4. Glazing and Coloring: Endowing Liuli with Gorgeous Colors
Glazing is the link that gives Liuli its colorful appearance. The glaze of traditional Liuli is mainly made of quartz and lead oxide, which is bright and transparent, and is a traditional formula for Liuli glaze. Craftsmen mix metal oxides (such as iron, copper, cobalt, and manganese) into the glaze as colorants to create different colors—for example, iron oxide for yellow and brown, copper oxide for blue and green, and cobalt oxide for deep blue.
The glazing method varies according to the shape of the blank: for flat or simple-shaped works, the blank is directly dipped into the glaze; for complex or delicate works, the glaze is brushed evenly on the surface with a brush to ensure that the glaze layer is uniform and free of bubbles. After glazing, the blank is air-dried again to avoid glaze flow during firing, which will affect the appearance of the finished product.
5. High-Temperature Firing: The Core of Liuli Making
Firing is the most critical and risky step in the Liuli making process, which directly determines the quality of the finished product. The firing temperature and heating-cooling curve must be strictly controlled—traditional Liuli is usually fired in a gas or electric furnace, with the temperature ranging from 1200℃ to 1400℃, and some complex works even require multiple firings. For lost-wax casting works, the gypsum mold with glaze is put into the furnace, and the temperature is raised gradually to make the Liuli raw material melt and flow into every corner of the mold, fully presenting the details of the design.
The firing process usually takes 15 days or more, and craftsmen need to monitor the temperature change at all times. If the temperature is too high, the Liuli will melt and deform; if it is too low, the glaze will not be fully fused, resulting in dull luster. After firing, the furnace cannot be opened immediately—instead, the temperature is cooled slowly according to a preset curve to release the internal stress of the Liuli, avoiding cracks caused by sudden temperature changes. This slow cooling process is also called "annealing", and some works need to be kept in a heat preservation kiln at 500℃ for four days to ensure stability.
6. Demolding, Polishing and Finishing: Creating the Final Beauty
After the furnace cools down completely, craftsmen open the kiln and demold the Liuli. For lost-wax casting works, the gypsum mold is broken to take out the Liuli blank, which is then cleaned to remove residual gypsum and glaze debris. The next step is polishing, which is a labor-intensive process—craftsmen use sandpaper of different thicknesses to polish the surface of the Liuli repeatedly, from coarse sandpaper to fine sandpaper, until the surface is smooth and bright, showing a gem-like luster.
Finally, craftsmen inspect the finished product carefully, repairing small flaws such as tiny cracks and uneven glaze. For works with complex patterns, they will also carry out secondary processing such as carving and inlaying to enhance the artistic value. Only the works that pass the strict inspection can be regarded as qualified Liuli products.
From raw material selection to final finishing, the making of Liuli goes through dozens of procedures, each of which requires the craftsman’s exquisite skills and full patience. As a carrier of traditional Chinese culture, Liuli not only inherits the ancient craftsmanship but also carries the pursuit of beauty of Chinese people. Every piece of Liuli, with its colorful luster and delicate texture, tells the story of the inheritance and development of this precious craft through thousands of years.