Ink Film Thickness and its Relation to Dot Size in Photo Offset Lithography

The relative ink film thickness of screen tints compared to nearby solid printing areas of two grainless lithographic plates were measured for dot areas from 45% to 95%, using a photometric technique of measuring the relative quantity of ink on a known area of the plate. Four different screen rulings were used - 65 I/in., 150 1/in., 300 1/in. and 500 1/in. It was found that there is no correlation between dot area and ink film thickness for the dot areas from 60% to 95% for the three coarser screens and from 75% to 95% for the 500 1/in. screen. The results do not exclude the possibility of a correlation for dot areas less than 75% for the 500 1/in. screen