With a black body or light trap behind the specimen, almost no light comes back from the backing, so the reading shows only what the single sheet returns. Low-grammage or weakly scattering sheets give an R0 well below their pad reading. Divided by R-infinity it gives printing opacity, and divided by the reading over an 89 percent backing it gives TAPPI opacity.
R0 dropped a full point on the lightweight trial, so opacity is going to fail before we even read the pad.
Also heard as
- single-sheet reflectance
- R zero
- black-backed reflectance
Related terms
R-infinity
Reflectance factor of a pad so thick that adding more sheets no longer changes the reading.
Black cavity
Light trap placed behind a single sheet so nothing reflects back from the backing during an R0 reading.
TAPPI opacity
Contrast ratio opacity: single-sheet reflectance over black divided by reflectance over an 89 percent white backing.
Printing opacity
Opacity calculated as single-sheet reflectance over black divided by the reflectance of an opaque pad of the same paper.