Tang Sancai and glazed pottery are traditionally fired at low temperatures, typically below 1000°C. The body is made from clay, a natural material primarily composed of hydrous lead silicates. This clay forms through the long-term weathering of feldspar rocks in the Earth’s crust. Its unique plasticity allows it to be molded into various shapes when wet, and once fired, it becomes dense and hard. The mineral composition of the clay varies depending on its source, which affects the final color and hardness of the finished piece.
The bodies of Tang Sancai and glazed ceramics are porous and prone to moisture absorption. The higher the porosity, the more likely they are to expand and swell when exposed to water. Many of these items were buried underground for centuries, allowing salts and impurities from groundwater to seep into their pores. When excavated, improper handling and unstable storage conditions can lead to salt crystallization within the ceramic structure. These crystals expand, creating internal pressure that causes the glaze to flake off and the body to crack or crumble.
Before any restoration work begins, it's essential to assess the condition of the artifact carefully. Avoid using harsh chemicals without proper knowledge. A detailed plan should be created based on the degree of damage. If the glaze is firm and the body is dense, two methods can be used: distillation water soaking or pulp paste treatment. For example, soaking the object in distilled water and changing the water every few days can help remove salts. Alternatively, using a pulp paste made from soaked paper can also be effective over several days.
If the glaze is weak and the body is fragile, water washing may not be suitable. Instead, a vacuum infiltration method can be used to reinforce the structure. The right mixture of reinforcing agents should be chosen based on the ceramic’s condition. After reinforcement, the surface should remain clean, without discoloration or shine. Methods such as spraying, brushing, or dropping the solution can be applied carefully, ensuring gradual and even coverage.
Common solutions used for cleaning and strengthening include 3% acetone in methyl ethyl ketone, 5–15% polyvinyl acetate in alcohol, 3% cellulose in alcohol, 2% nitrocellulose in acetone, and 5% polyvinyl alcohol solution. For dirt removal, 2% dilute hydrochloric acid can be used for limestone deposits, ammonium sulfate for gypsum, and 1% hydrofluoric acid for silica. Organic stains like food or smoke can be cleaned with ether, acetone, toluene, or sodium carbonate solutions. All artifacts should be rinsed in distilled water before further treatment.
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