We use specular gloss standard's calibrated to geometries of
20 - 60 - 85 degrees. We have a gloss black standard for high gloss readings and a matte white used for low gloss readings.
These come from BYK Gardner and are available from Thomas Scientific and Fisher Scientific. Cole-Parmer also carries standards.
They are somewhat expensive and need to be replaced if scratched. Use care when handling.
This is a little tidbit I picked up off the net. Might be usefull.