This false-coloured image illustrates the drainage of a fluid porous medium. The fluid (chloroform)and the porous medium (crushed silica) have similar refractive indices, so the system appears clear (green) when it is filled with fluid and opaque (black) when the fluid drains away. The fluid is draining away from below. The perimeter of the drained region is a fractal. Note the regions of trapped fluid inside the drained region ­ if you pretend that the porous medium is sandstone, and fluid oil, then you will immediately see a potential application of this research.