This technical report is applicable to the determination of the withstand characteristics of ceramic and glass insulators to be used outdoors and exposed to polluted atmospheres, on d.c. systems with voltages from ±1 000 V up to ±600 kV. These tests are not directly applicable to insulators made of organic materials, to composite insulators, to greased insulators or to special types of insulators (insulators with semiconductive glaze or covered with any organic insulating material). This report presents procedures for artificial pollution tests applicable to d.c. overhead-line insulators, substation insulators and traction line insulators. It may also be applied to bushings with suitable precautions to avoid internal damage and to hollow insulators intended for use in other apparatus. In applying these procedures to apparatus incorporating hollow insulators, the relevant technical committees should consider their effect on the internal equipment and the special precautions which may be necessary. NOTE - For largest objects such as large wall bushings and transducers, a high spread of test results has been experienced.