Bleedout 
The action of an entrapped liquid penetrant in surfacing from discontinuities to form indications.

Blotting
The action of the developer in soaking up the penetrant from the discontinuity to accelerate bleedout.

Contrast
The difference in visibility (brightness or coloration) between an indication and the background.

Dwell time
The total time that the penetrant or emulsifier is in contact with the test surface, including the time required for application and the drain time.

Developing time
The elapsed time between the application of the developer and the examination of the part.

Emulsifier
A liquid that interacts with an oily substance to make it water-washable.

Emulsification time
The time that an emulsifier is permitted to remain on the part to combine with the surface penetrant prior to removal. Also called emulsification dwell time.

Footcandle (fc)
The illumination on a surface, 1 ft2 in area, on which is uniformly distributed a flux of 1 lm (lumen). It equals 10.76 lm/m2.