Originally Posted by ShrekNZ
I think they are referring to polishing using metal polisher NOT wax which will leave a residue probably decreasing the conductivity of the brush tubes.
I thought it was obvious I was referring to metal polishing cream.
Nothing must be left on the surface of either the brush tube or the brush itself.
The objective is to have as much contact between the copper tubes and the brush surface.
This is also one of the reasons that round, tubular brush hoods and brushes perform better than the conventional square ones. It is easier to manufacturer the round tubular brush hoods with tighter tolerances and thus have maximum contact between the brush hoods and the brushes.
This is also the reason that you must pay attention to keep both brush surfaces and brush tubes always clean, so they maintain maximun conductivity with each other while they remain smooth in their in-out movement, without binding.