Take a close look at the two pictures in Figure 18-1. In the image on the left, the hole in the center is actually a white circle that makes the life preserver appear to have a hole in its center. In Illustrator, white is a color that is really “there” — and it blocks anything behind it. In the second picture, the hole in the center really is a hole, revealing whatever is behind it (in this case, an alarmed passenger noticing just how few life preservers his ship has).
How is this remarkable feat accomplished? If you set the fill color for the white circle to None, just that circle becomes transparent, revealing the gray circle behind it — so that won’t work. The trick is to use compound paths. The Compound Paths command joins two or more paths in such a way that wherever the paths overlap, you get a hole revealing whatever is lurking behind the paths. Incidentally, this is how the holes in letters, such as O and P, are created, so that when you run type over an object, you see the object through the holes.
All you need to create a compound path is two objects — one to serve as a cutting tool and one to serve as a place to put the hole. Then follow these handy do-it-yourself steps (no safety goggles required):
Place the object that you’ll be using to make a hole in front of the object in which you want to cut the hole.
Select both objects with any selection tool.
Choose Object→Compound Path→Make.
Where the paths overlap, you get a see-through area — you know, a hole.
To make the paths behave normally again, select the objects and choose Object→Compound Path→Release.
Perform the same feat by using the Pathfinder palette and selecting the Subtract from Shape Area command from the Shape Modes section. For more details, see Chapter 4.