Here is a video I recorded the other day. It's basically an example of using dye to test a leak in a light niche gasket. The leak is in the upper right corner of the gasket the black dye instantly gets drawn in where the leak is at.
[youtube:13nv499v]nhtCP431X9Q[/youtube:13nv499v]
[youtube:13nv499v]nhtCP431X9Q[/youtube:13nv499v]