Since bodily tissues vary in density, X-rays are effective (thickness). A shadow image of the organ is produced because the quantity of radiation that can travel through each tissue and expose the X-ray-sensitive film varies. For instance, because bones are so dense, the majority of the radiation cannot reach the film. Bones appear white as a result on an X-ray. Less dense tissues, like the lungs, which contain air, permit more X-rays to pass through to the film and appear on the image as grayscale.