The first step in crack detection after a though cleaning is to spray the dye penetrant on the area of the part to be tested. You want to thoroughly saturate the area with the dye. Next, you let the dye sit for 10 to 30 minutes. The longer the better but you don’t want to be in a situation where the dye dries, then you have to start over.
Next, wipe as much of the dye off as possible, then lightly spray the area with the cleaner and get all the dye off the part. Don’t hose the part with the cleaner but lightly wet it and wipe all visible traces of the dye off.
Here is the cleaned part ready to have the developer applied.