Ed #11 Print It

Ink, Paper, Press

Even with the best design and preparation and the closest look at the proof, problems can still arise with the ink, the paper, the press, or any combination of the three.

Ink density is a big concern. If the ink layer is not dense enough, colors can look washed out and type becomes thin and pale. Too much ink can blur the images and make the type look fat. Getting the density right is the printer’s job and usually, you shouldn’t try to specify it. After a sheet is approved, however, it’s a good idea to write the densities along the color bar, in case you ever decide to reprint the project. Keep in mind, however, that densities and colors will change as the ink dries, so a sheet that is wet will not look the same as a dry one.

The toners used in most digital printing behave differently than conventional inks. After they are applied, toners are typically baked onto the surface at a high temperature. If the temperature is too hot, however, coated papers can blister.

Other common problems include flaking, or picking, and hickies. Caused by overly viscous ink, undried varnish, overly high printing speeds or poor surface strength in the paper, picking pulls off small fragments of the paper’s surface, producing small unprinted white dots on the finished product. While some presses automatically wash away pick-outs, it may be necessary to stop the press and wipe the fibers from the blanket and plate.

Hickies are small white doughnut-shaped imperfections that are most obvious in large areas of solid ink coverage and the shadows of halftones. They are caused by specks of dirt, dust, dried ink or paper fiber on the blanket or plate, which prevent ink from transferring properly. Hickies are difficult to prevent and, because they are caused by loose particles, may appear and disappear at random during the run.

You may also encounter moirés, offsetting, color shifts and gas ghosting. Doubling, caused by a slight second contact between the paper and the blanket, gives each halftone dot a tiny shadow. Scumming, which sometimes appears as a streak running the length of the sheet, is caused when the ink migrates into non-image areas.

While some issues are relatively easy to troubleshoot, the causes of others are not as clear. Dot gain—an expansion of the size of the halftone dot when it is printed—can darken tint areas and images. It can be caused by the printing film or the printing process. There is also optical dot gain, which is produced by light reflecting from the paper stock. Mottling, which makes images appear blotchy and uneven, can be caused by faulty ink transfer, improper ink and water balance, worn blankets or a poor paper surface. Slurring is usually caused by mechanical problems or ink that is too tacky.Mechanical ghosting can be caused by a number of factors, including high humidity in the pressroom and an improperly laid-out form.

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