Glasses used in the production of optical devices.
To make glasses for optics, an elaborate and demanding production procedure is required, which will make us understand how much work is behind simple eyeglass lenses.
Optical glass must have high isotropy values (isotropy means that a body, in this case the glass must have the same physical characteristics in every direction) to be transparent, homogeneous, able to support cold working.
It must also be free of defects, even the most invisible such as bubbles or striae.
Le optical properties of glass are defined and determined byrefractive index and the variation of the same index as a function of the different wavelength of the light rays (dispersion).
Because the optical glass has these characteristics it is important the initial mixing phase. This operation of union takes place in furnaces crucible in platinum at 1000 ° C, with further increases in temperature according to the type of glass treated (up to 1800 ° C).
This mass that has been made remains to rest and cool for weeks, sometimes even months to prevent the devertification.
Another technical term that iindicates a change in the physical state of matter. In this way the products that are formed are crystalline and give X-ray diffraction.
The process involves a very slow annealing phase, the resulting glass is crushed and then shaped into standard shapes.
Optical glasses are classified according to the Abbe number, according to the following:
- Crown, glasses with Abbe number greater than 50.
- Among these we have the crown-borosilicates, light, clear and not very dispersive, containing boron, And crown-barium, whose particularities are due to the addition of barium to their composition.
- Flint, very dispersive glasses, with a high refractive index, contain percentages of lead and barium.
