Color Separations and Trapping

Trapping is a solution to a very annoying problem that arises in professional printing. Specifically, misalignment occurs when two colors overlap each other. This can result in an unpleasant visual effect and the colors not appearing correctly in the finished project. Look at the graphic below, where the blue circle is overlapping with the red circle. This is a classic example of where trapping is needed. 

There are tools that can assist you in fixing this problem. In the Pathfinder menu, on the very last part of the window, you will see a button for trapping. First, select the items that need trapping and select the trapping option.  

The menu opens and you are given several options. The top setting, "Thickness," is what you need to be concerned with. This will be a variable setting and it is best to consult with the specific print shop to get the optimum setting. Don't just put in what you believe to be the optimum setting. You could be wrong and the print job might turn out botched. 

After you enter the suggested setting, click the "OK" button at right to apply this setting. In the graphic below, which was blown up at 400%, you can see that there is a thin white line separating the two colors from the graphic at top. This should solve any misalignment problems that might occur in the printing process. Again, it is very important for you to give the ideal trapping setting from the print shop. These days trapping is almost always done automatically at the print shop by special software, (thankfully) making it unnecessary for manual manipulation of the color plates.