OBA is the abbreviation for “Optical Brightning Agents” or optical brighteners.

Optical brighteners are additives that are used by paper manufacturers to make a paper look white and luminous.

To make a paper look white, it is important to add substances that shift the invisible ultraviolet spectrum between 320 and 400 nanometers into the visible range from 400 nanometers onwards. The paper is thereby bluish or fluoresces in areas that are just visible to the human eye so that our eyes perceive that as a brighter, bluish white. Color measurements are so easily corrupted by optical brighteners, for example, created profiles could be yellowish, because the meter is trying to correct the blue cast of the paper.

Many “white” papers have optical brighteners in it. Sometimes, the brightening effect will weaken over a relatively short period of several years, as the whiteness of the paper will vanish over time.