The Development History Of Crystal Glass

Crystal glass has a long history. In ancient times, due to the many impurities in the glass raw materials, the melting temperature was not high, the glass did not melt well, and there were a lot of unmelted sand particles, bubbles and other defects. At the same time, the raw materials contained a lot of colored metal ions such as iron, manganese, and titanium. Is opaque or translucent. In the 13th century, the Venetians used quartzite with less impurities and Levant's sodium-containing plant ash to melt them into colorless and transparent glass.

In the 15th century, the quality of raw materials was further improved. Using pure quartz sand and soda ash recrystallized from a boiling aqueous solution of plant ash from the lower reaches of the Ticino River, the transparency of the glass obtained was significantly higher than in the past, similar to crystal, so it was named Cristallo. A kind of soda-calcium crystal, its composition range (mass fraction) is [1] SiO2 70.0%~71.5%, Al2O3 0.8%~1.31%, CaO 4.07%~4.72%, MgO 1.47%~1.66%, K2O 2.84%~4.55% , Na2O 15.2%~16.8%, Fe2O3 0.25%~0.51%, MnO 0.26%~0.51%, SO3 0.19%~0.31%, Cl 0.62%~0.92%, P2O5 0.15%~0.24%, Fe2O3 and MnO are Impurities in mineral raw materials, Cl and P2O5 are impurities in soda ash from plant ash.

The composition of soda lime crystal glass is somewhat similar to that of modern utensil glass. The content of K2O+Na2O is relatively high, and the content of CaO+MgO is relatively low. The glass is easy to melt and is suitable for manual operation. After the 13th century, the Bohemians established more than a dozen glass factories in Bohemia (now Czech) and Silsia. In addition to using high-quality quartz sand as raw materials, they also Forest wood ash containing potassium carbonate, such as wood ash from beeth forests, is used as the raw material to introduce alkaline oxides, so a transparent glass with a higher refractive index, also called crystalex, is made in the literature. Different from Venetian crystal glass, it is called Bohemia Crystalex. Because it uses forest wood ash as the raw material, it is also called Forext Glass. Bohemian crystal glass is made of potassium calcium, containing SiO2 75%~77%, CaO 5%~6%, K2O 15%~17%, the refractive index of the glass is 1.48~1.49, this system is called potassium calcium crystal grass. Later, in order to improve performance, Na2O and a little B2O3 were added to the composition, which was renamed as potassium soda-lime crystal glass. The composition (mass fraction) of this type of crystal glass produced in the Czech Republic is SiO2 75.5%, B2O3 0.2%, CaO 6%, K2O 4.8% , Na2O 12.8%. The main producing area of potassium-calcium and potassium-sodium crystal glass is the town of Nov Bor, 90km away from Prague. The technical indicators of the product are: density 2.444g/cm3, refractive index nD (20℃) of 1.50002, average dispersion ( 20℃) is 830×10-5, linear expansion coefficient is 89.1×10-7℃-1, acid resistance (according to ISO 719 standard, 0.01mol/L HCl at 98℃, the weight loss per unit area of the glass surface) is 1.98 mg/dm2, liquidus temperature 950℃[2].

In the Middle Ages, Bohemian crystal glass manufacturing technology gradually spread to Central and Western Europe. Glass factories in Britain and France mostly used Bohemian potassium-calcium and potassium-soda-lime glass components, which had a relatively high melting temperature and required fine wood as fuel. A large number of forests were cut down. In 1615, the British royal family banned the use of high-quality wood as fuel for glass factories, which affected the production of glass factories. In 1670, the British Ravenscroft discovered that the addition of PbO to the glass composition not only reduced the viscosity and melting temperature of the glass, the glass was easy to melt, the material was long, the shape was convenient, and the gloss of the glass increased, making it more crystal clear, and easy to grind. , Put lead glass into production, called lead crystal. The refractive index, dispersion, and density of lead crystal are higher than those of Cristallo and Crystalex, and the melting, forming, and engraving properties are better than those of Sodium-Calcium and Potassium-Calcium crystals, so they are popularized.

Most of the world's famous crystal glass factories were established around the 18th century. In 1764, Ranaut established a glass factory in a small village in Baccarat, France. It was a small family workshop at the time, producing plate glass, mirrors, and crystal glass imitating Bohemia. When Ravenscroft invented lead glass, Pakistan Cara also makes lead crystal, which contains 24% PbO, which is called full lead crystal. The production of colored crystal glass began in 1830, and later it produced opalescent crystal glass, translucent imitated opal glass and imitation agate glass. Later, green opalescent crystal glass was introduced. Colored and opalized crystal glass became the characteristics of Baccarat. At the Paris Exposition in 1855, Baccarat exhibited a 5.182m (17ft) high crystal glass candlestick and a 7.010m (23ft) crystal glass fountain base; in 1972 at the International Fair in Lisbon, Baccarat exhibited A crystal glass sculpture of the earth and the moon weighing 90.72 kg (200 lbs). Over the past 150 years, although the property rights have changed hands many times and the name of the factory has changed several times, Baccarat’s brand has always been deeply rooted in the hearts of the people. In France and even in Europe, Baccarat is thought of when it comes to lead crystal.

In 1783, George and William's uncle and nephew established a glass factory in Waterford, England, to produce full-lead crystal glass containing 30% PbO. The first British World's Fair was held in London in 1851. The designer Paxton used pig iron to prefabricated beams, columns and roof trusses, and used Watford glass for walls and roofs to create a transparent crystal palace with a length of 563m and a width of 563m. 124.4m, the shape is a stepped cuboid, with a roof on it, the total construction area is 74000m2, the total glass area is close to 9300m2, called the Crystal Palace Exhibition (Crystal Palace Exhibition), opened a new era of glass architecture, in the history of world architecture An important position.

Compared with the historic Venetian and Bohemian glass, Swarovski crystal glass is only more than a hundred years old. The Swarovski company was founded in 1895 by the Czech Daniel Swarovski (Daniel Swarovski) who immigrated from Bohemia to the town of Wattens in Austria. Swarovski manufactures high-lead crystal glass containing 32% PbO. It is particularly famous for using high-lead crystals as imitation diamonds (rhinestones), rubies, sapphires, amethysts, titanium sapphires, Indian rubies, and translucent and opaque opal glasses. Such as white opal, violet opal, aquamarine opal, olivine, tourmaline, topaz, etc. Swarovski created a precedent for applying crystals to fashion, shoes, hats, and watches, and expanded the application range of high-lead glass.

In the 1820s, the Saint Petersburg Royal Glass Factory in Russia produced large-volume vases, jugs, urns and furniture. In 1828, a blue sofa with crystal glass was made for the king of Persia.

Although the people of Chu in the Warring States Period of China have used quartz sand, galena, and barite as raw materials to make decorative glasses such as sword heads, swords, and jade pieces of lead-barium silicate glass, these glasses are translucent or The opaque dark glass is obviously different from modern lead crystal glass. After the Western Han Dynasty, the composition of glass made in China changed from lead barium silicate composition to lead glass composition, and glass with better light transmittance was produced. Ancient literature believed that the appearance of glass was similar to crystal or jade at this time, which served as a substitute for jade. , But from the physical point of view, these glasses can not be called lead crystal glass.

Lead glass developed by China in the 1950s was mainly flint glass for optical glass, which was used as an optical material. Lead glass for radiation protection was developed in the 1960s. It was in the 1970s that Dalian, Shanghai and other utensil factories developed true medium lead (PbO>24%) and high lead (PbO>30%) crystal glass.

In recent years, some well-known traditional ware glass factories in China have basically stopped producing lead crystal glass due to various reasons. There are two types of enterprises that produce crystal glass. One is the large-scale enterprises that produce optical glass and special glass. Optical glass production equipment and technical advantages, the production of lead crystal glass; the other is a joint venture or private enterprise, which uses imported continuous melting electric furnaces to produce high-lead or medium-lead crystal glass.