Also called the intrinsic reflectance factor, it is measured on a stack of the same paper, often 10 or more sheets, so the backing behind the stack has no influence. Brightness, whiteness and color are reported on R-infinity unless a single-sheet value is specified. Together with R0 it is the input for printing opacity and for the Kubelka-Munk scattering and absorption coefficients.
Your pad was only six sheets of 48 gram, that isn't R-infinity; keep adding sheets until the reading stops moving.
Also heard as
- R∞
- intrinsic reflectance factor
- pad reading
Do not mix it up with
- R0: R0 is a single sheet over a black cavity; R-infinity is an opaque stack of the same paper.
Related terms
R0
Reflectance factor of one sheet measured over a black cavity, the starting point for every opacity calculation.
Printing opacity
Opacity calculated as single-sheet reflectance over black divided by the reflectance of an opaque pad of the same paper.
Kubelka-Munk theory
Two-flux light model linking a sheet's reflectance and opacity to its scattering and absorption coefficients.
Pad
Lab talk for a stack of sheets thick enough to be opaque, used for R-infinity, brightness and color readings.
Reflectance factor
How much light a sample sends back compared with an ideal white diffuser lit and viewed the same way.