Just to add my experience, I've found it much easier to discern the orientation of the outer foil on film caps using TrueRTA spectrum analyzer software on my laptop. The most expensive version of this software (1/24 octave resolution) is only $100, lower resolution versions cost less.
I use the line in connection on the laptop with a simple cable consisting of a mini jack on one end and bare wires for signal and ground on the other, then watch the 60Hz peak on the spectrum analyzer go up or down depending on cap orientation. I also own a Tektronix 20 MHz scope and the TrueRTA method works much better for me.
I use the line in connection on the laptop with a simple cable consisting of a mini jack on one end and bare wires for signal and ground on the other, then watch the 60Hz peak on the spectrum analyzer go up or down depending on cap orientation. I also own a Tektronix 20 MHz scope and the TrueRTA method works much better for me.