The fringes produced by ordinary glass are mainly due to the uneven mixtures, corrosion of refractories (mainly introducing Al), and agitation in the manufacture of glass products.
Therefore, optical glass should start from these aspects, the purity of raw materials is more than 99%, impurities are less than 100,000 parts, as well as the size of raw materials, weighing has high requirements. Ceramics or platinum are used as refractories in melting furnaces. Generally, only pouring, rolling, cylinder breaking and liquid forming methods are used to effectively prevent the agitation of glass in the process of forming.
In addition, the structure of the furnace is different from that of the daily glass furnace. It is divided into melting pool (charging), regulating pool (adjusting melting atmosphere), refining pool (clarifying), homogenizing pool (mixing). The daily output of the large furnace is only 5 tons.