A barium swallow is a diagnostic procedure for the esophagus and the stomach where a patient swallows barium sulphate, which blocks x-rays, and then is subjected to flouroscopy. The material coats the esophagus, allowing it to be seen as a hollow tube. It is usually used with sodium bicarbonate, which creates gas when swallowed, which doesn't block x-rays at all and shows as white areas.
The test involves exposure to a fair amount of radiation, and should be avoided in pregnant women and children. As the barium sulphate will irritate tissues outside of the digestive tract, it should also be a avoided if a tear is suspected.