Manufacturing method and apparatus of optical material

A manufacturing method of an optical material, the method comprising:

• blending an inorganic compound (a) containing at least one of a sulfur atom and a selenium atom and a compound (b) represented by a following formula (I) in a tank, the compound (a) and the compound (b) being blended at a ratio of 1 mass % or more and 50 mass % or less of the compound (a) and 50 mass % or more and 99 mass % or less of the compound (b) relative to a total mass of a mixture of the compound (a) and the compound (b);
• mixing a compound (c) containing at least one thiol (SH) group;
• preliminarily polymerizing at least the compound (a) and the compound (b) by blending and polymerizing the compounds in the tank;
• cooling the compounds;
• and
• deaerating the compounds, wherein
• the compound (c) is mixed during any one of the preliminary polymerizing, the cooling and the deaerating,
• a viscosity of the obtained composition is measured during at least one of the preliminarily polymerizing, the cooling and the deaerating, and when the viscosity reaches a predetermined value, a control is performed to terminate an ongoing one of the preliminarily polymerizing, the cooling and the deaerating and start a succeeding one of the preliminarily polymerizing, the cooling and the deaerating,
• when the control is performed during the preliminarily polymerizing, the control is performed so that the viscosity is kept at or lower than the predetermined value, and
• when the control is performed during the cooling after the control is performed in the preliminarily polymerizing, the cooling is terminated when the viscosity reaches a second predetermined value that is larger than the predetermined value
• (m represents an integer of 0 to 4, and n represents an integer of 0 to 2).