This standard specifies the test method for determining the time-dependent hardening effect of rubber due to low-temperature crystallization using hardness measurement. The method is applicable to raw rubber, unvulcanized rubber, and vulcanized rubber, particularly materials such as chloroprene rubber and natural rubber that exhibit a significant tendency to crystallize at low temperatures, but it is not suitable for materials that crystallize rapidly. To perform the test, the specimen must be placed in a constant-temperature low-temperature test chamber that provides a stable low-temperature environment. At specified time intervals, the change in hardness is measured within a very short period using a rubber hardness tester (such as a Shore hardness tester or an International Rubber Hardness Degree tester). The degree of crystallization is characterized by the increase in hardness.