Under a long-wave UV lamp, brightened papers glow blue-white while brightener-free sheets stay dull and purplish gray. Labs use it for quick checks on grades that must be free of brightener, such as some food-contact, archival and photo-base papers, and to spot contamination from brightened broke. Uneven glow also reveals size-press streaks and poor mixing.
Hold the reel sample under the black light; if it glows, somebody fed brightened broke into the OBA-free grade.
Also heard as
- blacklight
- UV lamp
Related terms
OBA
Optical brightening agent: a dye that absorbs UV light and re-emits it as blue, making paper look whiter.
Fluorescence
Light a sample emits after absorbing UV, measured in paper as the gap between UV-included and UV-excluded readings.
Broke
Paper made on the machine that will not be sold as is, and is repulped and fed back into the stock.