Chapter 3 Section 3 Independently Created Glass in Ancient China

According to the examination of unearthed cultural relics, from the perspective of the world, there is no doubt that ancient Egypt was the first country to invent glass.The oldest glass objects unearthed there are those from the "predynastic period" of 3400 BC.Quartz sand is abundant along the banks of the Nile, and trona is abundant on the shores of Egyptian lakes near Alexandria. There are many opportunities to use them, and glass will be smelted by accident.For example, when potters mix calcite or dolomite powder with trona into clay and quartz sand powder as pottery slurry (for the sake of beauty), there will be dripping glaze drops in the kiln, that is, glass beads.The basic composition of this glass is obviously NaO-CaO-SiO, the so-called soda-lime glass.In ancient times, the firing technology of this type of glass spread from Egypt to the Mediterranean coast, Persia, the two river basins of West Asia and India, and was introduced to my country around the Han Dynasty.In short, this kind of glass is widely produced and circulated all over the world.

Chinese traditional ancient glass has its own independent development system.In recent decades, some glass tube beads have been discovered from Western Zhou tombs in Henan, Shaanxi, and Shandong. In particular, Hunan Museum has unearthed a large number of ancient tombs from the Warring States and Han Dynasties in Changsha, Hengyang, Changde, and Xiangxiang. The glass of the period is mainly some ritual vessels with Chinese national characteristics, and seals with Chinese literature and moral concepts. Most of them have decorative patterns and patterns with Chinese national decorative characteristics, indicating that they were made by Chinese ancestors.The chemical composition of these glasses is completely different from the glasses in Egypt and other ancient civilizations. They all belong to the PbO-BaO-SiO or PbO-SiO system, that is, the glass using PbO as a flux.If the glass of the Tang and Song Dynasties is tested again, it will be found that the glass of the PbO-KO-SiO system appeared again.In conclusion, a unique glass system using PbO as a flux has been circulating in ancient China.

We speculate that the invention of this lead-based glass came not from the inspiration of pottery, but from experience in metallurgy.Based on the fact that most of the lead-barium glass unearthed by archeology comes from Chu and Hunan, that area has been rich in lead since ancient times, and now it has been found that the mineral used is galena, and this type of method Lead ore is also often associated with barite (BaSO).It can be imagined that during the Western Zhou Dynasty and the Spring and Autumn Period and the Warring States Period, when ceramic crucibles and earthen kettles were used to oxidize and roast this kind of galena, once the lead oxide came into contact with the clay components on the inner wall of the pottery, the container wall would have a high temperature of 800-900 °C. , a layer of moist and bright lead glaze will be formed on the walls of the pot and kettle, so that the craftsmen can get the initial inspiration.This kind of lead glaze fell off after knocking, much like jade, so they gradually and consciously smelted it with lead ore calcined ash mixed with clay and quartz sand, and it became the earliest glass in my country.If the galena used is mixed with intergrown barite, then the resulting glass will naturally contain BaO.

In the Eastern Han Dynasty, in order to make more pure and transparent glass, artificial lead red (PbO) or yellow lead (PbO) was used to make glass.These two kinds of lead oxides are all produced by oxidation of metallic lead, or first made into lead powder [PbCO·Pb(OH)] and then roasted into lead red and yellow lead.Because the BaO component in the ore cannot be reduced into metallic lead in the process of smelting lead, it is impossible for the glass smelted with lead red and yellow lead to contain BaO anymore.Therefore, the lead glass produced thereafter becomes the PbO-SiO system.After the Tang Dynasty, glass of the PbO-KO-SiO system appeared all over the country, that is, the composition of KO was added, which was the result of the progress of the red lead process.Because the original two methods of making lead pellets were not economical or efficient enough, in the Tang Dynasty, a process of combining metallic lead, sulfur, and saltpeter (KNO) to make lead pellets appeared, which greatly improved the production efficiency and was soon popularized. .For example, the alchemy work "Danfang Jingyuan" published in the mid-Tang Dynasty records: "Every catty of lead, two liang of sulfur, and one liang of nitrate are used to make alchemy (Huang Dan). When boiling, add a small piece of sulfur, continue to add a little nitrate, add vinegar after boiling, add a little nitrate and yellow, and the yellow will disappear after boiling. Stir-fry is the end, and it becomes yellow dan." Yellow Dan must contain a large amount of KSO, and the glass sintered with it will of course increase the composition of KO, and change it to a PbO-KO-SiO system.

There is a kind of boron glass in modern high-grade glass, that is, borax is added to the raw material, which belongs to the NaO-CaO-BO-SiO system.In fact, this kind of glass has also been tested in ancient my country.In an alchemy work of the Tang Dynasty, "Jinhua Yuye Dadan", there is an interesting formula of "glazed medicine": "Glass medicine, use half a catty of lead Huanghua (that is, Huangdan), add 2 liang of nitrate, boron [ Sand] two liang, big fire fan to make juice." Unfortunately, this glass recipe was not popularized in our country, and it was lost in the future.Because borax was transported from Tibet to the Central Plains during the Tang Dynasty ("Danfang Jingyuan" records, borax came out of Guozhou. Now Nanchong, Sichuan), the road is difficult and dangerous, and the traffic is inconvenient. Only a few alchemists and medical experts use it occasionally.

Of course, a considerable part of the ancient glassware unearthed in my country, especially after the Han Dynasty, is soda-lime glass.Some of these glass devices are imported from abroad or imported as tributes, and some are manufactured by our country in imitation of foreign countries. In short, its manufacturing technology is not independently created by our country.There are many records in the ancient books of Chinese literature and history about the introduction of glass (called colored glaze before the Tang Dynasty) products from abroad.Yan Shigu of the Tang Dynasty commented on this sentence: "The Great Qin Kingdom produced ten kinds of colored glazes: blue, yellow, black, white, red, red, turquoise, cyanotic, purple, and green." Great Qin generally refers to the Eastern Roman Empire.The glass here should refer to glass."Baopuzi Neipian" written by Ge Hong, a master of alchemy in the Eastern Jin Dynasty, said: "For foreign countries to make water essence bowls, they are actually made of five kinds of ash. Today, there are many people in Jiaotong and Guangxi who have obtained the method and cast them." This artificial "water spirit" (now known as crystal) is of course a colorless glass.This statement further indicates the introduction of glass casting skills.

It should be pointed out that the development of ancient glass technology in China is slow, and the application of glass products is not popular. From the Warring States Period to the Tang and Song Dynasties, it is generally limited to making some decorative glass beads, glass tassels, glass earrings, or making glass instead of jade. Bi, glass grapes, glass gourds and other handicrafts, while ignoring their practical value.After the Ming and Qing Dynasties, there were more workshops and workshops producing glass products, especially in Shandong, which became an area rich in glass, but they could only make small things such as lampshades, cups and bottles, which are collectively called "feeders" as the saying goes.Plate window glass and other large glass shipments are still imported.If we look into the reason why my country's ancient glass technology is backward, it is probably because our country has developed exquisite porcelain-making skills very early.In ancient times, the molding and processing of porcelain was relatively easy and convenient for mass production; porcelain was strong and not easy to break; it would not burst due to sudden heat; its raw materials were simple and cheap; Reduced demand and interest in glass, thus affecting its development and progress.