Gradients can allow for the illusion of 3D objects, and because Illustrator uses vectors, the objects and gradients you create can be scaled up or down without loss of quality. Thus, Illustrator is a great tool for product design and mockups, and can be used in place of, or in conjunction with 3D software.

In this Illustrator tutorial, you’ll learn how to use gradients in Illustrator to create a pair of iPod Nanos, and how you can quickly create a variety of other objects using these techniques.
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design.creativefan.com/using-gradients-in-illustrator-to-create-an-ipod-nano/