Should Direct Hand Contact with the Glaze Be Avoided to Prevent Corrosion by Hand Sweat in the Maintenance of Qing Dynasty Black Glaze Kiln-Changed Porcelain?
Introduction
The Qing Dynasty witnessed the pinnacle of Chinese ceramic craftsmanship, and black glaze kiln-changed porcelain, with its unique and unpredictable color variations and exquisite textures, stands out as a precious treasure in the history of Chinese ceramics. These artworks not only embody the superb skills of ancient craftsmen but also carry profound cultural connotations, making them highly sought after by collectors and cultural heritage enthusiasts worldwide. However, due to the passage of time, the physical and chemical properties of Qing Dynasty black glaze kiln-changed porcelain have become relatively fragile, and scientific and reasonable maintenance is crucial to ensure their long-term preservation. Among the numerous maintenance issues, a common concern is whether direct hand contact with the glaze should be avoided to prevent corrosion by hand sweat. This article will systematically explore this question, combining the material characteristics of Qing Dynasty black glaze kiln-changed porcelain, the chemical composition of hand sweat, relevant case studies, and practical maintenance skills, aiming to provide comprehensive and scientific guidance for the preservation of these precious cultural relics.
Core Analysis: Why Hand Sweat Poses a Threat to Qing Dynasty Black Glaze Kiln-Changed Porcelain
To understand the impact of hand sweat on Qing Dynasty black glaze kiln-changed porcelain, it is necessary to first analyze the chemical composition of hand sweat and the material properties of the porcelain's glaze. Hand sweat is a complex mixture containing water, electrolytes (such as sodium chloride, potassium chloride, calcium ions, and magnesium ions), organic substances (such as lactic acid, urea, and amino acids), and microorganisms. Under normal circumstances, the pH value of hand sweat ranges from 4.5 to 7.5, showing weak acidity or neutrality, but when the body is in a state of fatigue, excitement, or high temperature, the acidity of hand sweat will increase, and the concentration of various components will also rise.
The glaze of Qing Dynasty black glaze kiln-changed porcelain is mainly composed of silicates, along with metal oxides (such as iron oxide, copper oxide, and manganese oxide) that produce kiln-changing effects. Although the glaze is relatively dense after high-temperature firing, it is not completely impermeable. After hundreds of years of natural aging, microcracks (known as "crazing") often appear on the surface of the glaze, and the glaze layer may also have slight porosity. When hand sweat comes into contact with the glaze surface, the water in the sweat will penetrate into the microcracks and pores, and the electrolytes and organic acids in the sweat will undergo chemical reactions with the components in the glaze.
On one hand, the chloride ions in sweat can react with metal oxides in the glaze to form soluble chloride salts. These salts will expand when they absorb moisture and crystallize when they dry, which will further expand the microcracks on the glaze surface, leading to the peeling of the glaze layer over time. On the other hand, organic acids such as lactic acid in sweat can corrode the silicate structure of the glaze, reducing the hardness and gloss of the glaze surface. In addition, microorganisms in hand sweat can multiply on the glaze surface, producing metabolic products that further accelerate the corrosion of the glaze. For black glaze kiln-changed porcelain, the unique kiln-changing color is formed by the specific distribution and oxidation state of metal oxides in the glaze. Corrosion by hand sweat will alter the content and distribution of these metal oxides, thereby damaging the unique aesthetic effect of the kiln change.
It should be noted that the degree of damage caused by hand sweat to the glaze is related to the frequency and duration of contact, as well as the state of the glaze itself. For porcelain with intact glaze and no obvious crazing, occasional short-term contact may not cause obvious damage, but long-term or frequent direct hand contact will undoubtedly accumulate damage, which is irreversible. For porcelain with already damaged glaze or obvious crazing, the corrosive effect of hand sweat will be more significant, and even a single contact may accelerate the deterioration of the porcelain.
Case Evidence: Damage Caused by Hand Sweat to Qing Dynasty Black Glaze Kiln-Changed Porcelain
There are many cases in the field of cultural relic preservation that prove the corrosive effect of hand sweat on ancient porcelain, including Qing Dynasty black glaze kiln-changed porcelain. One typical case is the "Yaozhou Kiln Black Glaze Kiln-Changed Bowl" collected by a regional museum in China. Before the 1990s, due to the lack of scientific maintenance awareness, the staff often took the bowl directly with their hands for display and research, and did not clean the glaze surface in a timely manner. After more than 20 years, obvious changes appeared on the glaze surface of the bowl: the original bright kiln-changing color faded, the glaze surface became dull, and a large number of fine cracks and small peeling spots appeared. Through scientific detection, the researchers found that the chloride ion content on the glaze surface was significantly higher than that of the same type of well-preserved porcelain, and lactic acid and urea residues were also detected. These substances are exactly the main components of hand sweat, which confirms that the damage to the bowl's glaze is closely related to long-term direct hand contact.
Another case involves a private collector who purchased a "Jian Kiln Black Glaze Hare's Fur Tea Bowl" from the Qing Dynasty. The collector was fond of the tea bowl and often held it in his hand to appreciate it, even using it to make tea occasionally. After only three years, the "hare's fur" pattern on the glaze surface of the tea bowl became blurred, the glaze color turned yellow, and small rust-like spots appeared. The collector sent the tea bowl to a professional cultural relic restoration institution for inspection. The results showed that the pH value of the glaze surface had decreased, and a large number of metal chloride and lactate crystals were detected in the microcracks of the glaze. The restoration expert pointed out that the main cause of the damage was the long-term contact of the tea bowl with the collector's hand sweat, and the tea water further accelerated the corrosion process. Although the tea bowl was repaired later, the original appearance and value of the cultural relic had been irreversibly damaged.
In contrast, a "Lang Kiln Black Glaze Kiln-Changed Vase" from the Qing Dynasty collected by the Palace Museum has been well preserved. The Palace Museum has strict regulations on the handling of cultural relics: all staff must wear clean cotton gloves when touching the porcelain, and direct hand contact with the glaze surface is strictly prohibited. At the same time, the display environment of the vase is strictly controlled, with constant temperature and humidity, and regular scientific cleaning and maintenance. After hundreds of years, the glaze surface of the vase is still bright, the kiln-changing color is intact, and there is no obvious corrosion or damage. This case fully shows that avoiding direct hand contact with the glaze surface is an important measure to ensure the long-term preservation of Qing Dynasty black glaze kiln-changed porcelain.
Practical Skills: Scientific Maintenance of Qing Dynasty Black Glaze Kiln-Changed Porcelain
Based on the above analysis and cases, it is clear that avoiding direct hand contact with the glaze surface is an essential part of the scientific maintenance of Qing Dynasty black glaze kiln-changed porcelain. In addition to this, there are many other practical maintenance skills that need to be mastered to ensure the safe preservation of these precious cultural relics.
First, in terms of handling, in addition to wearing clean cotton gloves (cotton gloves have good air permeability and can prevent sweat from penetrating, and avoid scratching the glaze surface), it is also necessary to hold the porcelain correctly. For bowls, plates, and other flat porcelain, they should be held from the bottom or the edge of the base; for vases, jars, and other three-dimensional porcelain, they should be held from the body and the bottom at the same time to avoid applying excessive force to a single part, which may cause the porcelain to break or the glaze to peel. It is strictly prohibited to lift the porcelain by its ears, handles, or other fragile parts.
Second, in terms of storage environment, the temperature and humidity should be kept stable. The suitable temperature for storing Qing Dynasty black glaze kiln-changed porcelain is 18-25°C, and the relative humidity is 50-60%. Sudden changes in temperature and humidity will cause thermal expansion and contraction of the porcelain, leading to cracks in the glaze and the body. Therefore, the storage location should avoid direct sunlight, proximity to heating equipment, air conditioners, and windows (to prevent rain and dust). It is recommended to place a hygrometer in the storage area to monitor the humidity at any time, and use a humidifier or dehumidifier to adjust the humidity when necessary.
Third, in terms of cleaning, if there is dust or dirt on the glaze surface, it should be cleaned in a timely manner, but violent cleaning is strictly prohibited. The correct cleaning method is: first, use a soft brush (such as a goat hair brush) to gently brush off the dust on the surface; then, soak a soft cotton cloth in deionized water or distilled water (avoid using tap water, which contains impurities and may leave water stains), wring it out until it is half dry, and gently wipe the glaze surface along the texture of the glaze; finally, use a dry soft cotton cloth to wipe the glaze surface dry. It is strictly prohibited to use chemical cleaning agents (such as detergent, bleach, and acid-base cleaners), which will severely corrode the glaze surface. If the dirt is difficult to remove, it is recommended to ask professional cultural relic restoration personnel for processing.
Fourth, in terms of display, when displaying Qing Dynasty black glaze kiln-changed porcelain, it should be placed on a stable and non-slip display stand to avoid collision and falling. The display stand should be made of soft materials (such as felt, foam) to prevent scratching the base of the porcelain. At the same time, the display area should be well-ventilated, and the number of people visiting should be properly controlled to avoid excessive carbon dioxide concentration and humidity in the air, which will affect the preservation of the porcelain. It is also necessary to avoid displaying the porcelain in a place with heavy oil fume, dust, or chemical pollution (such as kitchens, laboratories).
Conclusion
Qing Dynasty black glaze kiln-changed porcelain is a precious part of Chinese cultural heritage, and its scientific maintenance is crucial to inherit and carry forward Chinese traditional culture. Regarding the question of whether direct hand contact with the glaze should be avoided, the answer is undoubtedly yes. Hand sweat contains a variety of corrosive components, which can react with the glaze of the porcelain, causing damage such as fading of the glaze color, dullness of the glaze surface, cracks, and peeling. A large number of practical cases have fully proved the harmfulness of direct hand contact with the glaze surface.
To ensure the long-term preservation of Qing Dynasty black glaze kiln-changed porcelain, in addition to avoiding direct hand contact with the glaze surface (wearing cotton gloves when handling), it is also necessary to pay attention to the correct handling methods, stable storage environment, scientific cleaning methods, and reasonable display methods. Only by combining these maintenance measures can we effectively slow down the aging and deterioration process of the porcelain and keep these precious cultural relics intact for a long time.
In the process of protecting and inheriting cultural relics, every small detail may affect the life of the cultural relics. Therefore, we should establish a scientific awareness of cultural relic preservation, abide by scientific maintenance methods, and let these precious works of art from the Qing Dynasty continue to shine with their unique charm in the long river of history.