Crystal glass, also known as transparent glass, is a special transparent material that can transmit light with some tolerance. Crystal glass is widely used in modern life and has become an indispensable material in various industries.
1. Lead crystal
Lead crystal (lead crystal) is most commonly used for watchmaking, optical instruments and many other delicate products must meet a certain level of transparency requirements are impracticable to use ordinary glass. It is composed of two parts: 1/3% lead oxide (PbO), 2% calcium carbonate (CaC2O4), the remaining part contains traces of other metals such as sodium sulfide or potassium sulfide Na2S or K2SO4 The amount of impurities is less than 1%.
The lead content determines the transparency of crystal, the higher the lead content, the higher the degree of transparency. Lead oxide and sulfide sulfur components are in a solid solution state (the so-called “salt”) in glass crystals, which can effectively block ultraviolet rays to reduce visual interference of light passing through the crystal surface. However, if you need to be able to filter UV or infrared light (such as thin watch crystals), then it should not contain such compounds.
Lead glasses are usually produced by several processes: According to the different chemical composition
A few kinds of lead glass  have a high soda body with an alkali-free formula for optical use. The soda ratio may exceed 90%, the lead content does not exceed 8%. It is low in expansion, has good stress resistance, and high impact point.
Lead borosilicate glass has a high soda body with a sodium-free formula for optical use. The soda ratio maybe 86%, the lead content does not exceed 30%. Low expansion, good stress resistance, and high-temperature resistance.
According to different processes: Harder process (harder process) mainly contains lime water softening methods; Soft window (soft window) mainly in addition to lime as a fluxing agent also added iron oxide Fe2O3 or titanium oxide TiO2 used as reducing agent, is characterized by operation economy and less pollution generally. The main product: Mirror plate glass, mirror plate glass, glass mirror strip, and so on.
According to the different formulas: Lead borosilicate glass is a kind of lead-free crystal glass. Its main component is boric oxide BO2, its other components are usually composed of soda CaO or lime SiO2 with a small number of other ingredients such as potassium oxide KO, copper oxide CuO or aluminum oxide Al2O3.
In addition to the above methods such as compact process (compact process) can also be made into the crystal glass. The main products include an optical lens, industrial lamp cover, and electronic display screen cover; Crystal raw materials take sodium sulfate Na2SO4 instead of calcium carbonate CaCO3 in the raw material for the melting process, which can be made into crystal glass.
2. Quartz watch crystals
Quartz watch crystals are composed of two parts: 1/4% boric oxide (BO3), and 93.75% silica SiO2 in the metal components of other impurities such as Na2S or Ag content <0.01%. Crystal clear pure color and density, stability of physical properties, small expansion coefficient, and low-temperature resistance.
Quartz glass does not contain lead elements that will interfere with ultraviolet light vision is also has very good optical performance (See table for comparison between the performance characteristics of several types). The main raw materials are silicon dioxide sand ground to remove water and other impurities, then need a certain amount of heat treatment after being mixed with boric oxide and other additives.
Quartz glass is made of high-purity quartz sand, using the vacuum melting process to obtain transparent quartz ingot after heat treatment in the state of granular crystal appears, and then by grinding, polishing or cutting into a variety of shapes, sizes, and colors Quartz watch face into watches. Low expansion coefficient (no contraction in hot weather) , Bubble colorless clear, very stable physical properties (quartz glass under normal temperature conditions so long as no operation for more than 25 years has not been broken).
In addition to watch crystals prone to cracking means: First be sure that caused by excessive pressure on the crystal because rubbing against non-metallic objects are likely to cause damage to the glass. Second, if after a long time do not wear watches are usually stored in a drawer or folder outside of the box, it is likely to “freeze”, the air inside of the watch crystal pressure and gradually increase until it broke the window. Thirdly, if you use poor quality paint coatings on the watch face will be easy to peel off or flaking cover, resulting in strong friction due to its own weight slowly but surely damaged by themselves broken.
Quartz glass is a kind of compound substance formed from sand and other raw materials used in optical instruments making glasses, having high light transmission strength, excellent flatness, and transparency. Its main components are processed: Quartz (SiO2) — 92.5%, silicon dioxide 96% boric oxide (BO3.2) — 4.7%. The main characteristics of its excellent optical properties and the low coefficient of thermal expansion, good heat resistance, thermal shock resistance, impact resistance, and other areas are much better than ordinary glass.
Quartz glass in watches to form a compact watch crystal case is the most widely used material in watches, including but not limited to: Watch box or housing itself; Watch cover; Watch face, and so on. Glasses lenses were originally invented by French scientist Blondel · Conduyt in 1752 some German scientist Schott also produced glasses lenses with several different configurations in the same period.
For centuries since ancient times, people had been trying to find a transparent material to replace the conventional milky-white glass, but in vain until the latter half of the 19th century when scientists discovered that melted silica (silicon dioxide) , and the man-made process can be made into a transparent material, this discovery inevitably broke human beings long-term dream:
To make glasses. Since then many people have been trying to improve the optical transmission rate of glasses because there is still some slight interference, but it was not until 1880 by German scientist Otto Schott found boron-containing crystal structure from different angles to see through once again further increased. These discoveries are probably known today as “Schott Glasses”. With the increasing demand for watch crystals, its production capacity is also gradually improving.
Quartz glass is very durable, does not decay nor oxidize, so it is widely used in a variety of watches. Quartz glass can be said to be the world’s first transparent synthetic material if you don’t count diamond which still has “invisible” light transmission properties.