material science in a can

The other day I decided to be lazy and unhealthy and so I went to fix myself some canned food. What I saw inside the can, other than the food, were the patches on the internal wall.

On lamp post, yes. But I had never seen such patches inside a can before. Those are actually grains of polycrystalline material, such as steel. Anyway I don't really like material science.

Next time when you are waiting for the green man at the road crossing, don't hug the pole but instead take a look at the light pole/post. You will see similar patches.