Anatomy of a Roller
What does the surface of a roller look like?x_white
If you look under a microscope at a new roller surface it looks very uneven, full of fingers and ridges and gorges, almost like saw tooth mountain ranges. This roughness is created when the roller is made and the rubber stretches and breaks around the grinding wheel. The “mountains” add enormous surface area to a roller—and they move. When looking at them under a microscope you can see the ridges. This rough surface carries ink and water, and the constant agitating motion of the fingers keeps the ink and water in a uniform emulsion.
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Contrary to what some people think, rollers do not have pores. Pores are holes surrounded by a rigid surface. The surface of a roller is continuous ridges and valleys and entirely flexible.

Nap
From our normal perspective this rough surface of a good roller is called the nap. A good nap is essential for good printing. You can test for sufficient nap by pushing your index finger away from you down the axis of the roller. If the roller catches your finger, it has nap and will print well.
Some rubber compounds have very little nap. If a roller is smooth out of the box, it’s a defective roller for offset.

Glaze

With use, rollers tend to get glazed, which means the mountains become filled and sealed with particles from the many inks and solutions that the roller is subject to.
Rollers that have no nap or are glazed will not be able to keep the ink and water uniformly emulsified. This can cause ink and water inbalance, color variation, and other problems. Think of it as trying to paint with a new brush as compared to an old dried paintbrush. The old paintbrush cannot possibly lay down a smooth layer of paint. Remember this the next time you are struggling with a glazed roller that is causing printing problems.
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