Abstract: A dye is incorporated into the pressure medium used to test a vessel for pressure leaks. The dye is preferably fluorescent, and the vessel is preferably inspected using a light source which causes the dye to fluoresce. The pressure medium can vary widely, for example, air, other gas, water, or petroleum based pressure mediums can be used. When the pressure medium is gaseous, the dye is preferably atomized and introduced into the vessel along with the pressure medium. The site of any leaks is easily detected because of marking by the dye. The process eliminates the need for submerging the pressurized vessel or observing the vessel for pressure decay. The dyes used may remain within the vessel after the test procedure and have utility as a long term leak detection tool. Apparatus and leak detection methods are disclosed.