Four things on broken glass: 1) it produces more straight lines and not so much round bits, 2) before breaking it yourself cover one side with contact paper so that it doesn't explode everywhere (you can get clear contact paper which is a plastic really), 3) different glass produces different effects - plate glass (drinking glasses, mirrors, old houses have this, glass shelves are usually of this type, and some tabletops) breaks in mostly big chunks or in striations; tempered glass (like a patio door and double-paned windows) breaks into a million little bits - it will have a printed logo in a corner; and laminated glass (your car windshield and most commercial windows like at retail stores) is two sheets of glass glued together so breaking one pane might not break the other pane - look at the side edges and you can see easily, 4) the more lead in the glass (the edge will be green) the more crystalline it is and therefore prone to straight-line breakage - it also has that nice "ping" sound like in fine stemware. Ceramics break in big chunks and powder. Hard plastics break straight-line, similar to glass, and soft plastics break ragged-edge similar to paper but a CD cover works pretty well. Rusted metal is always good.

What you want is a good mix of big and small, straight and round so I might walk around the streets and look for potholes or broken concrete and photograph that. Or maybe find a mud puddle. You could always search the internet but who knows what you will find or how long that will take. Getting back to paper, fold it up and rip it up into small and big chunks then rearrange everything to fit but leave some gaps. Cheese slices are also good for this. If you have the means, take a flat pan and freeze a thin amount of water to make something like a pane of glass, then break the edges up with a big wooden spoon (don't hit it too hard or it will go everywhere just push on it), then photograph before it melts or sketch it if you're fast enough. Food coloring or Kool-Aid (don't know if they have that in Germany) can help you see things better. Chocolate also works pretty well with this method (since it's a solid at room temperature and easier to photograph but the chunks are not quite right). Take a candy bar, melt it into something thin, then freeze, then break it up. Magic Shell is liquid at room temperature so I don't recommend that - plus I don't know if they have that in Germany.

Well, anyways, those are some ideas. I guess you know why I call myself the mad scientist