dye pen alocrom effects

alright there guys
ive been questioned at work in the last few days on the affects of alocroming a component before a penetrant inspection and the affect this can have on the inspection
ive only been qualifyed for 6 months or so and i can only respond with what ive been told which was that alocrom can mask discontinuities but i cant say that i know this is true because im only going on one man opinion could anyone shead any light on this thanks allot guys cheers