This article presents an overview of a technique that involves the use of an inkjet printer to generate a series of continuous-tone progressive separations that will serve as visual guides on press.
By Joe Raymond
You will not be making a dot-for-dot progressive as in the case of the color key. Instead, the continuous-tone image from the inkjet will be dumbed down by using low resolution on most of the workflow settings needed to make the inkjet pleasing progressive. As a rule of thumb, print the pleasing progressive at 25% of the size of the screen-printed job. This gives a good scale of the visual data to the halftone image at 100%. As your line screen ruling in print goes up, the pleasing progressives from your inkjet may be scaled up to as much at 50% of the screened size. It is also desirable to print the progressives at one of the lower resolutions of the inkjet (for the stock being printed). All of these steps are taken to keep the contrast up and the tone range down in the progressive image, making it more like the halftone result at the screen press. There is no benefit in printing high-resolution, continuous-tone images for the progressives when you will compare them to halftone images on press at relatively low line-screen rulings and with a potentially smaller tone range.
Now open the file in Photoshop. Check immediately that you are viewing the file in CMYK color space. Next, set color management for the print. Remember to avoid high-resolution images and that you must create gray balance in your prints where expected. You will use the same digital file to make films for the screen press.
Decide what the print sequence will be. There are several schools of thought about the right printing sequence, but my recommendation would be to examine each channel independently in Photoshop (Figure 1). Clicking on the individual channels will convert each one to a monochrome (gray) preview image. The color data in the image file will not change.
Visually compare the cyan and magenta channels for percentage of coverage in print. The cyan or magenta channel with the most ink coverage is chosen as the first color in the printing sequence. This decision is based purely on reducing the potential for skipping and stacking in print. Yellow, technically, would be best down first, but most screen printers do not run that way. Yellow generally runs second or third in the screen printing sequence depending on the percent coverage. With very few exceptions, black should always run last.
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