What's in a capacitor?

 Whilst ratching in the cupboards, I found a capacitor that one of my predecessors had cut open. I've always been too compliant to wreck things!

I teach capacitors as two metal plates with a gap between usually filled with an insulator. Here we should have two aluminium foil strips with paper in between that has been soaked in an electrolyte. Now if you roll that up, you'd have the aluminium shorting as the strips touched each other and so a second paper strip makes a four layer stack to be rolled. It doesn't look like this one has survived intact. 

There are good pictures and diagrams here.