Chapter 2 Section 2 China's Ancient Porcelain and Its Chemical Achievements

Porcelain is developed on the basis of the production experience of white pottery, imprinted hard pottery and glazed pottery. The technological processes such as raw material selection, washing and refining, processing mud, casting and kiln firing are all borrowed from various The pottery process, or basically the same.However, there is an essential difference between porcelain and these three types of pottery, that is, there has been a leap forward and breakthrough in raw material selection and firing technology.So what are the conditions to be regarded as porcelain?Although there is no complete agreement on this issue so far, there are several recognized items: First, the matrix material should be white china clay. The main components of this clay are feldspar and quartz. It has a high content of AlO, The basic oxide content is low, and the FeO content is extremely low (generally below 2%), which is different from clay, so the porcelain body is white.Second, it must be fired at a high temperature. Generally, the firing temperature of ancient Chinese porcelain is 1150-1300°C, and the carcass is basically sintered.However, the composition of porcelain clay produced in various places is different, and the firing temperature is also not the same, so it mainly depends on whether it is sintered.Third, a layer of glass enamel is applied to the surface.Fourth, the water absorption rate of the utensils after firing is less than 1%.This is related to the firing temperature. The higher the temperature, the higher the degree of sintering of the carcass, and the lower the water absorption of course.Fifth, the carcass is hard and the wall is thin. When knocked, it will make a crisp metallic sound, which is very pleasant, and it seems translucent when viewed against the sun.The first three chemical factors are the most basic of these conditions.It can be seen that the invention of white pottery, hard pottery, and glazed pottery prepared material and technical conditions for the creation of porcelain in these most basic aspects.

Of course, the emergence of porcelain also has a process.Celadon ware appeared in the Shang Dynasty.The carcass composition of this kind of utensils is quite different, some of them are close to china clay, the iron content is less than 3%, the carcass color is grayish white, light yellow, gray green or light brown, and the firing temperature is generally as high as 1200 ℃. The carcass is basically sintered, and the section often shows shell luster, and the water absorption is also quite low. The combination of lime glaze and carcass is quite firm.These characteristics show that the green glaze ware basically meets the conditions of porcelain, and has already reflected the requirements of porcelain in essence, but the whiteness of the body and the uniformity and transparency of the glaze still need to be improved. Therefore, some ceramic historians tend to call it This kind of blue-glazed ware is "primitive porcelain".

The original porcelain developed to the Eastern Han Dynasty and gradually evolved into real porcelain.The glaze of this early porcelain is still a simple lime glaze, and there is no artificial colorant added, and it is still blue (fired in a reducing atmosphere), so it is called celadon. In 1924, early celadon porcelain fired during the Eastern Han Dynasty and Emperor Shi was unearthed in Leigutai, Xinyang, Henan.Since then, many celadon wares from the Eastern Han, Three Kingdoms, and Jin Dynasties have been unearthed in tombs all over the country.Among them, the celadon tiger son unearthed from the Eastern Wu tomb in Zhaotugang, Nanjing, and the celadon sheep unearthed from another Eastern Wu tomb in Qingliangshan, Nanjing are regarded as superior works of celadon in the Han and Jin Dynasties.However, the celadon wares of this period were mainly Ming wares, which had not yet entered the homes of the common people.The research results on Han and Jin porcelains show that compared with the original porcelain, the porcelain making technology has made two major advances: first, the relative content of acidic and neutral oxides SiO and AlO in the porcelain clay raw materials of the carcass has increased, and the relative content of alkaline oxides has increased. CaO, MgO, KO and NaO are all relatively reduced, which requires the firing temperature of celadon at least above 1200°C, so the vitrification degree of the fetal bone is improved, the texture is harder and less deformed; second, The color of celadon glaze is relatively pure, which requires that the content of iron (FeO) in celadon lime glaze should be controlled between 1 and 3%, and the temperature and ventilation of the kiln must be strictly controlled.If the iron content is too high or the ventilation rate is too large, more iron will be in the state of FeO, which will make the glaze color turn yellow or even dark brown.This shows that the porcelain workers of the Jin Dynasty had rich experience and strict control over the selection of porcelain clay and glaze.

Since then, the raw materials and processing of the porcelain body have not changed much, and the energy of generations of porcelain workers is mainly devoted to the improvement of enamel, glaze color and painting technology, and they are constantly introducing new ones. Chinese ancient porcelain is famous both at home and abroad for its delicate texture, lustrous glaze, and rich colors, and is praised and appreciated by people from all walks of life; and because of its long history, it reflects from a certain aspect the development of social economy, culture, and art in various periods of ancient China. achievement and has thus been meticulously studied by historians, sociologists and archaeologists.Ceramic scientists and chemical historians, while appreciating these art treasures, pay more attention to the quality of porcelain body, the composition of glazes, the raw materials and processing of colorants, the causes of brilliant colors, the control of kiln temperature and atmosphere and its influence on glaze colors. The mechanism of influence, that is, the chemical connotation in the porcelain making process, because it reflects the chemical achievements of ancient China from another aspect.Moreover, strengthening the physical and chemical research on ancient porcelain is also crucial to inheriting and carrying forward the fine tradition of Chinese porcelain making technology and developing modern porcelain products.

Chinese porcelain glazes have appeared since primitive porcelain, and high-temperature lime glazes have been used for a long time.According to the analysis results of the chemical composition of high-temperature glazes in past dynasties, since most of them contain AlO very high, generally 10-15%, it can be judged that the glaze is mainly made of lime and white clay.It is said that Ru Kiln in the Song Dynasty actually used agate instead of porcelain clay to make glaze, and agate was quite pure quartz.The firing temperature of this type of lime glaze needs to be about 1000°C.In the Liao Dynasty and the Southern Song Dynasty, lime-alkali glaze appeared in the black glazed porcelain of Guantun Kiln in Liaoyang (gang Gang) and celadon of Longquan Kiln, that is, plant ash (rich in KCO) was added to the glaze. Its characteristic is that it has a high viscosity at high temperature and is not easy to flow glaze, so the glaze layer can be thicker.Therefore, in traditional Chinese high-temperature glazes, the alkaline components are mainly CaO, KO and NaO, the neutral oxides are AlO, and the acidic components are SiO.In the Ming Dynasty, some low-temperature glazes appeared in Chinese porcelain.One is the traditional lead glaze, which is the main body of Chinese low-temperature glaze; the other is the low-temperature glaze that replaces yellow dan as a flux with tooth salt (actually the main component is KNO), such as some Chenghua glazes. yellow glaze.However, low-temperature glaze has low hardness, is easy to wear and scratches, and has poor chemical stability. It is easily corroded by water, carbon dioxide gas and acid mist in the air, and halo phenomenon occurs, so it is not widely used.

Among the high-temperature color glazes of ancient Chinese porcelain, green glaze, red glaze, black glaze and blue glaze occupy the main positions, while white glaze is an important basis for obtaining various gorgeous glaze colors.The whiteness is very high, and the color will be bright and pure only after adding coloring agent.Around the time of the Tang Dynasty, the level of craftsmanship of white glaze in my country was very high and reached a mature stage. At that time, the white porcelain of Xingzhou (now Xingtai, Hebei) and Dayi Kiln of Sichuan were famous for their cleanness and luster. The texture is excellent, the iron content in the glaze is very low (less than 1%), and the elutriation process must have been rigorous.This created conditions for the development of various colored glazes and painted porcelain after the Tang Dynasty.

The coloring agent of celadon glaze is iron oxide, which is an inherent impurity in the glaze at the beginning, and it is of course difficult to control the color tone after firing.After the Tang Dynasty, porcelain workers have gradually been able to adjust the iron content in the glaze by adding ocher based on white glaze based on experience.The coloring effect of green glaze is produced by the dissolved FeO in the glaze, so the pure and bright color quality mainly depends on the ratio of FeO/FeO in the glaze. Obviously, the higher the ratio, the brighter the turquoise, and the lower the ratio, yellowing.Therefore, the complete maturity of green glaze lies in the strong reduction of the firing atmosphere in the kiln.The celadon porcelain of Zhejiang Longquan Kiln in the Song Dynasty had a bright glaze and was as transparent as a mirror. Its representative works, the pink celadon ware and the plum celadon ware, were as verdant as plums in color and luster, reaching the pinnacle of the beauty of celadon glaze color.

At the beginning, the high-temperature red glaze probably used malachite [CuCO·Cu(OH)] or bile alum (CuSO·5HO) as the coloring agent. Colloidal copper presents a red color.The Jun Kiln Porcelain of the Song Dynasty was the forerunner of the red copper glaze ware.However, the appearance of Jun porcelain is not completely red, but the glaze color on the back and bottom is a fluorescent blue with different shades. Therefore, viewed from the whole body, the glaze color of this kind of red glaze porcelain is as beautiful as the sunset in the blue sky.According to scientific tests in recent years, the appearance of this peculiar opalescent phenomenon and elegant blue luster is due to the suspension of numerous spherical, SiO-rich glass dispersed phases in the transparent glaze layer.Since the particle size of the dispersed phase is between 40-200nm, which is much smaller than the wavelength of visible light, it will more strongly reflect short-wavelength blue-violet light, thus presenting a beautiful blue opalescence.The chemical composition of this glaze is characterized by low AlO content, high SiO content, and 0.5-0.95% PO, indicating that apatite may have been added to the glaze.In the Yuan Dynasty, the porcelain kilns in Jingdezhen, Jiangxi Province initially fired red glaze wares, but only small utensils such as plates and bowls.In the Yongle and Xuande years of the Ming Dynasty (AD 1403-1435), Jingdezhen finally produced bright red copper-red glaze ware with a deep and moist glaze layer, which is very lovely. There are "ruby red", "ji red" and "ji red". and other names.It is extremely difficult to fire this kind of porcelain. Not only must the firing atmosphere be strictly controlled, but also the proportion of copper ingredients must be very appropriate. Therefore, there were very few craftsmen who mastered this technology at that time, so after Jiajing , The technique of copper red glaze was once lost.It was not until the late years of Emperor Kangxi of the Qing Dynasty that this craft was restored. The red glaze ware fired was called "Langyaohong", which was more pleasing to the eye than the red glaze of the Ming Dynasty. The traces of bleeding are like dripping blood, so it is also known as "chicken blood red" or "pig liver red".

The coloring agent of high-temperature black glaze is iron oxide, and the iron content in the glaze can be as high as 5-6% (calculated as FeO).Iron oxide is in the state of FeO in a high-temperature reducing atmosphere, so the glaze layer is black or caramel.This kind of glaze also often contains traces of other colored metal oxides, such as MnO, CoO, CuO, CrO, etc., which may be introduced from iron ore powder, and they will also have a certain impact on the glaze color.Of course, pure black glaze does not make people feel pleasing to the eye, but there is a type of "crystallized glaze" that has aroused great interest among ceramicists at home and abroad.For example, the so-called "oil drop spot glaze" and "rabbit hair spot glaze" fired in Jianyang kiln in Fujian Province in the Song Dynasty are quite famous and outstanding representatives of this kind of black glaze, and they are a wonderful work among Song porcelains.On the surface of the oil drop glaze, there are many silver-gray round beads that look like oil drops and have metallic luster, much like the twinkling stars in the night sky, so the Japanese call this glaze "Tianmu glaze".There are silver-gray filaments on the surface of the rabbit hair spot glaze, some are like feathers, some are like branches, some are like clumps of rabbit fur, and some are radial needles, which is very unique and interesting.According to scientific tests in recent years, the iron content of "oil drop" and "rabbit hair" is about 10 times larger than that of the surrounding vitreous body.Observed under a microscope, these small "oil droplets" and fine "rabbit hairs" are actually composed of a group of dense granular or fibrous hematite (FeO) and a small amount of magnetite (FeO) small crystals, so ceramic technology experts Our preliminary judgment is that the formation of "oil droplets" and "rabbit hairs" is due to the effect of crystallization of iron oxide in these places when the enamel is cooled after firing.As for the different shapes of "oil droplets" and "rabbit hairs", this is related to the degree of supersaturation of iron oxide and the cooling speed of the kiln temperature.

The high-temperature blue glaze only appeared in the Yuan Dynasty. The coloring agent is CoO, and the coloring agent used is black cobalt mineral powder, which is called "pearl material" and "painting bowl green" in China.At the beginning, all porcelain kilns in my country used domestic pearl material, which was a kind of cobalt-containing pyrolusite.After Yongle and Xuande in the Ming Dynasty, blue and white materials such as "Sumaliqing" and "Huhuiqing" were introduced from abroad successively. They are a kind of cobalt ore containing iron and nickel.Due to the influence of MnO and FeO-NiO, the two blue glazes have different hues, the former is elegant and the latter is rich and colorful.To burn this kind of blue glaze well, it is very important to control the atmosphere in the kiln. After the glaze starts to melt, a reducing atmosphere must be created, and it needs to be neutral in the later stage.A sapphire blue-glazed gold colored bowl of the Yuan Dynasty was unearthed in Baoding, which is a fine piece of this type of porcelain.

The book "Tiangong Kaiwu" has detailed records on the porcelain glaze technology of the Ming Dynasty (Figure 1-5). Low-temperature color glazes for porcelain products are rarely used, and the main colors are green, yellow, red and purple. The low-temperature green glaze mainly inherits the traditional lead glaze with copper as the coloring agent.Since the Song Dynasty, there have been special commercial copper flowers (the copper flowers produced in Beijing in the Qing Dynasty are a kind of gray black powder, the main components are CuO and CuO, and there are a small amount of metallic copper, SiO, FeO, AlO, the total copper content About 96%, of which CuO accounts for 79%) instead of malachite ore.In addition, during the Chenghua period of the Ming Dynasty (AD 1465-1487), a kind of malachite green porcelain appeared, called "Fa Cui Porcelain", which also used copper flowers as the colorant, but used nitrate as the flux.The patina glaze fired with this kind of glaze can reach the degree of emerald green, which is similar to peacock feathers, green and elegant, and very pleasing.It is obviously developed from "Fahua pottery".At the beginning, a kind of daily-use glazed pottery with special decorative effect and unique local style was popular in southern Shanxi.Among them, those colored with copper flowers are called "facui", and those colored with blue and white materials are called "falan", commonly known as "fahua ware". The coloring agent of low-temperature yellow glaze is mainly alum red, so it is called "iron yellow". The FeO content in the glaze is about 4%. It is fired in a strong oxidizing atmosphere at a firing temperature of 800-900°C.However, it was not until the low-temperature yellow glaze fired during the Hongzhi period of the Ming Dynasty (1488-1505 A.D.) that its hue showed a true pure yellow, reaching the highest level of low-temperature yellow glaze in history.Some of them belong to tooth enamel.After Kangxi, antimony yellow glaze with SbO as the coloring agent appeared again, but this variety was introduced from abroad. The purple low-temperature glaze appeared very late, and did not appear on the "plain three-color" until the Guangxu period of the Qing Dynasty (1875-1908 A.D.).Its main coloring agent is manganese oxide, while trace amounts of iron and cobalt play the role of toning.According to the formula of Jingdezhen in modern times, this kind of manganese-containing coloring agent is called "Qingzhu", which is also a kind of cobalt-containing pyrolusite, which is produced in Ganzhou, Jiangxi Province, and is a black lump. The coloring agent of my country's traditional low-temperature red glaze is "aluminum red".The raw material for making vitriol red is vitriol, namely ferrous sulfate (FeSO·7HO).After roasting and rinsing green alum, a very fine "aluminum red" powder FeO can be obtained. The color is vermilion, very gorgeous, and the price is cheap.The alum red glaze in the Jiajing period is divided into two layers, the lower layer is high-temperature lime glaze, and the upper layer is lead glaze colored with alum red, containing about 10% FeO, and the alum red particles are suspended on the surface of the upper glaze layer, so this red color is FeO is what gives the color, not Fe dissolved in the glaze. After the 20th year of Kangxi in the Qing Dynasty (1681 A.D.), another kind of golden red glaze appeared in Jingdezhen porcelain.The formula of this golden-red material was introduced from the West.It is a purple-red stannate gold (AuSnO SnO 4HO) that is reduced by dissolving SnCl or metal tin into the aqua regia solution of gold.This red color is the coloring effect of colloidal gold in the glaze layer. Before the Song Dynasty, the fine art decoration on Chinese porcelain paid attention to engraving, scratching and printing, which was relatively monotonous.Since the Cizhou kiln in the Northern Song Dynasty invented the use of a brush dipped in pigment to paint on the glaze, it has created a new realm for the artistic processing of porcelain (Figure 1-6). Color painting has actually appeared since the Tang Dynasty.At that time Changsha Wazaping kiln had underglaze paintings in brown, red, green and other colors, but at that time it was only a few.Cizhou kiln porcelain is a kind of underglaze black color, which is painted with iron ore powder.Although there are a lot of output and works, they are only popular in some porcelain kilns in some parts of the north. Because the patterns and stripes of paintings are black or sauce-colored, they are not very colorful, and the works are mainly medium and low-end daily necessities such as porcelain pillows and bottles. Still not considered a work of art.It was not until the underglaze blue and white and underglaze red porcelains came out that they caused a sensation. Chinese porcelain painting can be roughly divided into two categories: underglaze color and overglaze color.The underglaze color is that the porcelain worker uses a brush to dip the very finely ground color material (colorant), and draws the pattern on the dry porcelain body or the plain porcelain that has been baked at a low temperature of about 800 ℃, and then hangs it. Lime or feldspar glaze slurry is fired at a kiln temperature of 1100-1300°C.The color materials used are ocher, blue and white materials or copper ore powder, etc., and do not need to be mixed with glaze.This kind of color painting is a major innovation of Yuan Dynasty porcelain.Among them, blue and white porcelain is the most outstanding and far-reaching, followed by underglaze red porcelain.Blue-and-white porcelain uses blue-and-white materials as coloring agents to depict various patterns, even figures of flowers and birds, and then fires them in a reducing atmosphere after being glazed.This kind of colored porcelain with white ground and blue flowers has a fresh style and rich colors. The ancients praised it as "blue and white flowers are quiet" and "the five colors are too gorgeous, so fresh and elegant, while the blue and white flowers are more colorful and elegant".Underglaze red porcelain is still painted on the plain body with malachite powder or copper flower pigment, and then covered with transparent lime glaze. It is still fired in a strong reducing atmosphere just like the above-mentioned red glaze, so it appears under the glaze. Colloidal copper-colored red decorations and paintings are one of the major inventions of the Jingdezhen porcelain kiln that flourished during the Yuan and Ming dynasties.However, firing is extremely difficult. Among the works that have survived so far, there are very few pure and bright colors. Overglaze color is developed on the basis of underglaze color technology.From the "Doucai" of the Ming Dynasty (a kind of painted porcelain that combines the underglaze color and the overglaze color, echoing each other, and competing for splendor) to the Kangxi five colors, the Qing three generations of pastels and enamel colors, the patterns are constantly refurbished. There are many varieties and the progress is rapid.With this kind of color painting, the simple color glazed porcelain products took a backseat, so that some famous historical kilns, such as Zhejiang Longquan kiln and Hangzhou official kiln, which were famous for firing monochrome glaze, fell into a state of depression. .Therefore, the birth of glazed porcelain is another important milestone in the development history of China's porcelain industry. The overglaze color is to first mix the fine powder of colored minerals with a low-temperature glaze matrix (called "glaze fruit" in modern times) composed of dental salt-huangdan-quartz stone newly invented at that time, and mix them in an appropriate proportion. , Grind evenly, use oils (such as tung oil, olive oil, persimmon oil) to make a coloring material, dip it with a brush, paint on the fired plain white enamel, and then bake it at a low temperature of 800 ° C to develop color into painted. The glaze color materials used in the Ming and Qing Dynasties mainly include the following: The traditional Chinese red color material is mainly alum red.As mentioned above, during the Kangxi period, golden red material was introduced from the West. Its color tone is similar to that of rouge, so it is also called "carmine" or "magenta". It is mainly used for enamel and pastel. There are two kinds of yellow pigments: iron yellow and antimony yellow.Antimony yellow is used in enamel and pastels, and the formula of this yellow material was introduced from the West. The coloring agent of blue color material is still blue and white material, but its chemical composition is slightly different from that of blue glaze, and it often contains some copper, so the color tone is also different. The coloring elements of purple are cobalt, manganese and gold, which are mainly used in enamel. It is estimated that it is made of gold red material and cobalt blue material. The main coloring elements of black color are iron, manganese, cobalt and copper.This colorant may be formulated with "Called Beads" and "Bronze Flowers".According to its chemical detection, it is found that no nitrate is used in its ingredients, and the loss on ignition is as high as 14-26%. It is estimated that kraft glue was added.This kind of color material is mainly used to outline the outline and veins of the branches and leaves in the picture, as well as to describe the outline pattern of the edge of the porcelain. White color is actually a kind of glass powder.The white color in Kangxi enamel is a kind of arsenic-containing milky white glass powder belonging to the KO-PbO-SiO ternary system, which is called "glass white" in Jingdezhen. The so-called "enamel color" is a kind of overglaze painting technology that was developed around the Kangxi period. It obviously borrowed from the cloisonne technology that emerged in the Ming Dynasty.The color material of this process is called enamel powder. It uses quartz powder and kaolin as the base material, uses yellow dan and borax as the flux, and adds an appropriate amount of colored metal minerals. After grinding, mixing, heating and melting, it is poured into The water is quenched, so that a colored glass mass is formed, which is ground into powder enamel.When used, it is mixed with glue, dipped with a brush to paint on plain white porcelain, and then baked at low temperature to form enamel.However, compared with the cloisonné glaze of the Ming Dynasty, Kangxi enamel has added AsO to the composition, so the color is thicker and the color is crystal clear and moist. In addition, the picture is slightly raised, which increases the three-dimensional effect. At the end of Kangxi period, famille rose appeared in Jingdezhen porcelain.It became popular during the Yongzheng period (1723-1735 A.D.).This kind of color material is mixed with AsO-containing white powder and various traditional colorants. It is used to paint on plain white porcelain. After firing, AsO will opacify the color, so the painted scenery is amazing. People feel opaque, like a thin layer of powder, which is elegant and soft, so "pastel" is also called "soft color".Since the soft color, people have called the arsenic-free traditional pigment and painting as "hard color" or "ancient color". During the Yongzheng period, enamel and pastels reached a fully mature stage.The colors are extraordinarily magnificent and elegant, and the tones are complete and pure. They are specially used to depict flowers and birds, bamboo stones, pine plums, landscapes, figures, etc. on porcelain that is "thin, light, firm, and thin" and as white as snow. The thick and light tones resemble pictures, and are accompanied by extremely exquisite corresponding poems, thus becoming an art treasure combining porcelain making technology with poetry and painting. In the early Qing Dynasty, as the social economy entered a prosperous period, China's porcelain production and porcelain craftsmanship reached a historical peak during the Qianlong period, which became the golden age of ancient Chinese porcelain.