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The Principle Of Lead Glass

Jun 17, 2021

Glass is composed of different proportions of a certain alkali metal silicate (sodium silicate or potassium silicate) mixed with one or more calcium and lead silicates, with addition of barium, aluminum, manganese, magnesium, etc. A molten homogeneous mixture. 

There are many varieties of glass according to its composition (for example, Bohemia glass, crown glass, lead crystal glass, lead oxide glass, Strass lead glass). These different types of glass are amorphous (amorphous) and all are transparent. Crown glass is the manufacturing material of traditional optical lenses. The ingredients are silicon, soda and lime, of which 60%~70% is silicon dioxide, and the rest is calcium oxide. Mainly used to make bottles, flat glass and optical glass. The most important characteristics of optical glass are refractive index n, dispersion (expressed as the reciprocal of Abbe number V) and specific gravity SG. Nd = the speed of helium light in vacuum/the speed of helium light in optical media. Vd=(nd-1)/(nf-nc) ”In the formula, the c and f lines are red and blue, and the wavelengths are 486nm and 656nm. The higher the value of V, the lower the dispersion. SG is the ratio of the weight of an object of equal volume to the weight of water. Optical glass with Abbe number>50 is usually called crown glass, and optical glass with Abbe number<50 is called flint glass, but not all optical glasses are classified according to this, the most commonly used is the 6-digit marking method , The first 3 digits represent the fractional part of the refractive index, and the last 3 digits represent the Abbe number. For example, the crown glass logo for glasses is 523590. The widely used optical glass in the market is mainly three kinds of materials: glasses crown glass, flint glass and crown glass. Crown glass has a refractive index of 1.523 and an Abbe number of 59. It is mainly used in the far vision zone of single-lens, double-lens and multifocal lenses. Flint glass, with high refractive index (approximately 1.580~1.690), large dispersion (small Abbe number, approximately 30~40), it is mainly used to make sub-pieces of fusion bifocals and high number lenses (high refractive index can make The thickness of the lens becomes thinner despite the increase in its weight). Crown glass, refractive index 1.541~1.616, Abbe number 55~59, mainly used to make sub-pieces of fusion bifocals. The same medium has different refractive indexes for various colors. Take crown glass as an example. Its refractive index for red light is 1.513, the refractive index for orange light is 1.514, and the refractive index for yellow light is 1.517. The refractive index of light is 1.519, the refractive index of blue light is 1.528, and the refractive index of violet light is 1.532. When light passes through glass, it cannot pass through 100%. For a piece of glass, part of the light is reflected when it passes through the front and back surfaces, so only 80 to 90% of the incident light passes through. The amount of reflected light is related to the refractive index of the lens. Taking ordinary crown glass as an example (refractive index is 1.5), the reflected light on the front surface of the lens is 4%, and the reflected light on the back surface is 3.8%. Regardless of light absorption, the light transmittance of crown glass is only 92.2%.