Here you can see the + leaves are clean and smooth. The - leaves are darker and discoloured.
I also noticed the leaves are made of different metals.
Another thing I noticed while unwrapping it, because it still had a little voltage left
the - leaves (buggered ones) were very slightly warm to touch. I thought I can't be feeling it right at first but I compared it to the + leaves and they were stone cold, there was a definite difference.
Anyway it wasn't quite as dramatic as I had hoped with the build up of crap on the leaves but I have a better idea on how they are put together now.