Here is a prime example why insulator manufactures moved away from Aluminum alloy hardware. As you can see in this shot, the caps encouraged "carbon tracking." This is a fancy way of saying that the hardware slowly "pulled" the current over the length of the porcelain during times of humid weather and rain until a path to the ground was completed. More and more of these aluminum based suspensions as well as line posts which were sold in the 1960's and 70's are being swapped out due to pole fires caused by flash overs. This was just another learning curve that had to be experienced before it could be discovered.