A Method for the Measurement and Specification of Process Ink Transparency.

Laboratory proofs of the SWOP/NAPIM standard reference inks were made over the black portion of a standard opacity chart at a range of film thicknesses normally used in offset printing. Colorimetric measurements of the original black bar as well as the same area after overprinting were made with a spectrophotometer and the overall color difference (Delta E) calculated using the non-overprinted black as a reference. A graph of Delta E* versus ink film thickness was made and the inverse slope of the linear regression line is taken as a measure of transparency of the ink. This method was originally developed at FOGRA in 1984. Its practical application was confirmed in conjunction with NAPIM and the test method finalized during the ISO TC130 WG3/4 revision of ISO 2846.