Coudray explains how following time-honored recommendations for pairing halftone line coutns can lead to undesirable printed results.
The screen-printing industry is full of fascinating production recommendations and procedures that are based on common practice. But when we examine them closely, many accepted methods turn out to be entirely false or seriously flawed.
One of the production issues that areas containing the most misinformation has to do with halftone line count-to-mesh-count ratios. There are all sorts of ideas floating around out there. The two most common ratios I hear recommended to printers are to use either 3.5 or 4 times the mesh count to the halftone line count. This month's column will explore in depth the various components and how they interplay. By the time I am finished, you'll understand that precise prediction of ratios is impossible.
To begin, let's establish the basic scenario. Assume we have a specific halftone frequency that we would like to work with--say 65 lines/in. Using the most common recommendations and rounding to the nearest common mesh count, the suggested meshes to use for line count would either be 230 threads/in. (227.5) at a ratio of 3.5 times the line count or 255-265 threads/in. (260) using the ratio of 4 times the line count. These would be the minimum mesh count values to use. Higher thread counts would further reduce the possibility of moiré, but here we'll just focus on the recommendations.
Halftone line count
Now let's turn our attention to the halftone line count. We must consider two essential factors when it comes to line count: the real area the dot is covering and the effect of angling on the actual frequency of halftone dots.
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