Inorganic silicate glasses contain compounds of fluorine or sodium fluoride that provide glass silencing. In the process of technological guidance of transparent glass, crystals with a refractive index that differs from the refractive index of glass are isolated and make the glass opaque, which in appearance looks like "solid milk". Unusual crystallization of glass is called zaruhaniem and is characterized by the size (about 100nm, 200nm and 1mkm) of crystals and the number of crystals (about 100,000 PCs.) in 1mm3.