Three dog skulls from ‘Secrets of Bones’ hosted by Ben Garrod. The first image shows a regular dog skull; this contains both collagen, an organic compound, and calcium phosphate, a mineral compound.

In the images with the red gloves, another skull has been left in an oven for a few days. This has taken out all of the organic compounds, leaving just the mineral compounds. As you can see, this bone is too brittle to be of structural use.

In the images with the blue gloves, a skull has been soaked in formic acid for over a month. This removed the calcium phosphate from the bone but leaves the collagen. The surprising result is a very flexible skull.