When we refer to masks, we’re not talking about the kind you wear to Mardi Gras. Masking in Adobe® Illustrator® is a way to define parts of your artwork as being hidden from view. Rather than having to delete unwanted parts of your art, you can use a vector shape to define an area that acts like a window: Anything that appears within the borders of the shape is visible, and anything that falls outside its boundaries is not visible. The main benefit derived from using masks is that you aren’t deleting anything from your file, and once a mask is created, it’s possible to change the mask or the artwork behind it, as well as reposition the mask to show or hide different parts of your artwork.
When you use masks in a file and are required to make changes, you’ll never have to re-create art that you’ve already deleted. Instead, everything that you create is always in the file, and you simply choose what is or isn’t visible. Additionally, a mask allows you to instantly clip parts of an image or an object. By using a mask, you can do with one click what might take tens of clicks if you use pathfinder functions to chop up and delete parts of objects.
There are three different kinds of masks that you can create in Illustrator, each with its own benefits. A clipping mask allows you to specify a certain vector shape as a mask for other individual or grouped objects. A layer clipping mask allows you to specify a certain vector shape as a mask for all the objects within the same layer. An opacity mask allows you to use the luminance value of any object to create a mask for other individual or grouped objects. As you will see, this last type of mask—one of the most well hidden features of Illustrator—is also the most powerful.
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