PURPOSE: To enable the production of pressed lens even in normal atmosphere preventing the fusion of the lens to a mold and the reduction of even a PbO- containing raw material, by coating the surface of a glass material having low transition temperature with an SiO 2 film, placing the glass in a mold and hot-pressing the glass.
CONSTITUTION: The surface of a glass having a transition temperature lower than that of SiO 2 and preformed to a form capable of giving the form of finished lens by hot-pressing is coated with an SiO 2 layer having a thickness of 50W2,000Å e.g. by vacuum evaporation. The glass material is placed in a mold and hot-pressed by heating the material and the mold at a temperature above the softening point of the glass and ≤900°C. The SiO 2 coating layer on the glass surface prevents the fusion of the glass to the mold during compression molding and prevents the reduction of the glass even is the glass contains PbO. The molding can be carried out in normal atmosphere as well as in a neutral gas or reducing gas. It is not necessary to use a mold made of an expensive material.