Plain X-ray Chest and Abdomen

In plain x-ray you can recognize the following densities

Air is black : Lung fields are mostly black with branching white blood vessels traversing through to the periphery. Air in bowel is black.

Fat is gray seen in neck, axilla and chest wall. Fat provides contrast in abdomen enabling us to see bowel and other organs.

Liquid and tissues are white (liquid density): Heart and other mediastinal structures, liver, spleen etc appear white. You cannot distinguish cardiac chambers. You can see the aorta distinctly (except the arch), as it is on a different plane than the heart.

Bone is dense

Contrast : Barium, IV contrast etc.

Metal: Bullets, Screws, Metallic tips of catheters etc