An x-ray only shows density. 2 equally dense objects will look the same regardless of chemical composition. What you're​ likely seeing is computer enhanced ima

An x-ray only shows density. 2 equally dense objects will look the same regardless of chemical composition. What you're​ likely seeing is computer enhanced images, which may be giving you a false sense of the capabilities of x-rays. There are explosives with densities fairly similar to paper. A block of those explosives, and a block of paper would look very similar on an x-ray.