Mastering Opacity Masks in Illustrator

In Part 1 of Behind the Mask, we examined how to make masks in Adobe Illustrator. While masking presents a variety of uses, there is still one aspect I have not yet addressed. There's a little something called an opacity mask. Many designers may have never heard of it.

Opacity Masks

This may seem unrelated to clipping masks at first, but bear with me…
I've heard a few gripes over the years that Illustrator gradients can't go from a color to fully transparent. Some people get frustrated to the point they build files in Photoshop to work around the issue. The truth is, Illustrator can support gradient transparency… it just doesn't do it terribly intuitively.

Opacity masks are located under the transparency palette's flyout menu and will probably make your day. The principles behind opacity masking are the same as clipping masks only with the twist that you can have your masked object fade into transparency.

If you're familiar with layer masks in Photoshop, you'll quickly pick up the benefits of opacity masks.

Creating an opacity mask

1. You don't have to do this part of the process, but if you start by creating a color filled shape on your page, you'll be able to better see your results.



1a. Create an object on top of the previous one and color it blue, for example.

2. Now create your masking object. Here's where opacity masks differ from clipping masks - you'll need to give your masking object a gradient fill from black to white (we'll get to why later). Use the default illustrator gradient swatch for now.



3. Finally, select all the items to be masked and in the transparency flyout menu select "Make Opacity Mask."





4. Done! You should have an object that goes from opaque to fully transparent.



Looking back on your black-to-white gradient fill, anything that was black is completely transparent, and anything white is completely opaque. Not terribly complicated, but there are tons of neat things you can do by tinkering with the options.



I'll say this: It's not the easiest way to get transparent gradients… but it does the trick.

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The real beauty of a mask lies in its ability to be all things: organic, rigid, whatever you choose. You're not conformed to a box or circle, your shapes can be as complex as you'd like, and masks allow you to retain the integrity of any hidden image information - all the while remaining fully editable.

With some practice, you'll be a master of masking in no time.

Anthony Fonseca is a graphic designer in the Greater Toronto Area. You can contact him with questions, comments or invites to masquerade balls by e-mailing him at anthony@5thdesign.com.