Brushes for Smudges
Custom brushes are essential for achieving that smudged, misprinted look. You can download some nice premade brushes from http://www.surfstation.lu/13.html. To load these new brushes into your Photoshop brushes palette, go to your brushes window (choose Window, Show Brushes) and click on the arrow in the top-right corner of the window. From the options menu that appears, select Load Brushes. Then simply locate your newly downloaded brushes file and click on it. Your new brush patterns appear at the bottom of your brushes palette. (You might need to scroll down to find them.)
To create your own custom brushes, start with a 30x30-pixel document. Next, create a pattern in that document. You can use noise filters, draw lines yourself, or use any combination thereof. Once you get a pattern you think you like (you won't really know until you use it), open your brushes window and click on the arrow in the top-right corner. From the options menu that appears, choose Define Brush. Your newly created brush pattern now appears at the bottom of your brushes palette. Experiment with creating brushes until you get some that you like.
After you've selected the desired brush from your brushes palette by clicking on it, it's time to paint. Click on the pencil tool, and select a foreground color. For lo-fi grunge purposes, merely dab the brush; don't actually paint with it. You're trying to create a corrosive effect, not draw a line. You can create either an ink smudge or a misprint.
To create an ink smudge, match your pencil color to the color of the text you want to smudge. Next, create a new layer for your smudges, making sure your smudge layer is above your text layer. Next, click your pencil near the edges of your text. This might take some trial and error, but when you do it correctly, it appears as if a printing press has smeared some extra ink while printing your text. This is one way to begin "eroding" the sterile digitality of computer-based design.
To create a misprint effect, match your pencil color to the background color of your page. Next, create a layer for your misprint effects, and place your misprint layer above the other layers of your design that you want to effect. Then, click your pencil on an area that you want to seem misprinted. It should look as if the page's background is showing through your design, as if the "printing" in that particular area got worn off or didn't quite take.
These brush techniques are subtle, and they might not seem to make much difference. But God is in the details. Your visitors won't notice exactly what you've done, but they will notice that your site looks differentless digital and more physical.