Over the years, I've gotten plenty of emails about how to create a seamless diagonal pattern in Illustrator, so here we go! Illustrator comes with some default pattern brushes, but no diagonal love. Diagonal patterns are a bit more tricky to make than a simple horizontal, or vertical pattern, but with some rock solid alignment, and some manual input into the Transform palette, you'll be making diagonal patterns in no time. Let's get started.
1. Start with a “square” artboard.
It doesn't really matter what size but if you want to follow along, I'm using a 600px x 600px artboard.
2. Create your vertical line.
Again, the size and shape is up to you here.
3. Align your shape to the top right corner
Here we are going to be using the Transform palette to make or shape align exactly to the upper left corner. Select your shape and in the Transform, set the “X” value to 0, and the “Y” value to 600 (or the document size you chose). The middle of your shape should now be aligned exactly to the upper left corner.
4. Rotate 45 degrees.
Next, rotate your shape 45 degrees either using your mouse and holding Shift, or right click, and enter the value in manually.
5. Duplicate your shape and align it to the opposite corner.
Now we need to duplicate or shape, and align it the same way we did above, but to the opposite corner. Again,select your new shape, and using the Transform palette, set your X value to 600 (or the document size you chose) and the Y value to 0. Now your two shapes should be aligned perfectly to opposite corners of the artboard.
6. Make a Blend between the 2 shapes.
Using the Blend tool click on 1 of your shapes, then immediately click on the other to make a blend. Then double click on the Blend tool, and you should see the ‘Blend Options” dialogue box. Set it to “Specified Steps” and then select a number that you think looks good. I recommend making this an odd number. You should have something that resembles the image below.
7. Expand your blend.
Select your new blend, and then go to Object > Expand, then click “OK.”
8. Create a square to crop with.
Select the Rectangle tool, and click once on the artboard. You can now enter in the exact dimensions you want your square to be. Set it to 600 x 600px (or the document size you chose), and click “OK.”
9. Align your square to the artboard.
Select your square, and in the Align palette, make sure you have “Align to Artboard” selected.
Now hit these 2 buttons to align your square exactly on top of the artboard.
Do a Select All (Command/Control + A), and then hit the Crop button in the Pathfinder palette.
Now you have a nice, seamless diagonal pattern that can be put to use.
If you want to add this pattern as a Pattern Swatch, just select it, and then go to Edit, Define Pattern, and it will appear in your swatches palette.