Patterns in Illustrator have a great number of uses and with all of those generous designers out there on the internet, we have many unique designs to put to use in our own projects. All of these resources that can be found around the internet are great, but have you ever come across one that you really loved the design, but really wish you could alter it just a little bit?
I'm sure that alot of people already know about this, but in case you didn't know, there is a way to change a pattern in Illustrator without having to completely re-do it. Whether you would like to change the color of a pattern or just alter it a bit, here is a quick tip on how to edit an existing pattern swatch in Illustrator:
Step 1: Pull up the pattern that you wish to alter (we'll use one of the default patterns that ships with Illustrator).
Step 2: Click and drag the pattern onto your artboard.
Step 3: Ungroup the pattern by either hitting ctrl+shift+G or going to Object > Ungroup.
Step 4: Make whatever changes you want (here, we just changed the colors)
Step 5: Select the entire thing and go to Edit > Define Pattern. Name your pattern whatever you like and we're done.
There are a few important notes on altering an existing seamless pattern:
First is, you need to make sure that the perimiter of the design remains the same or else the pattern will not fit together.
In Illustrator the pattern is defined by an unfilled, unstroked box that sits behind all of the elements (see image below). This box determines what bit of the design actually shows up when you finally make it a pattern. If you ever have trouble with the pattern not filling in properly once you have defined it, chances are it is because the bounding box isn't set up properly.
To reset the portion of the pattern that will be used:
1: Re-draw an new square using the rectangle tool. Make sure that the new square fits within where the old one was.
2: Make sure that it doesn't have any fill or stroke color.
3: Send it to the very back of the design. Either hit ctrl + shift + [ OR Object > arrange > send to back.
4: (Optional) With the square still selected, add some crop marks by going to Filter > Create > Crop Marks. This isn't necessary, but it helps you keep a handle on where your pattern will be cropped.
5: Select the whole thing and go to Edit > Define Pattern
Name your pattern and you are done. These steps could also be used to create your own pattern. Just do steps 1-4 and then fill in the area inside the box with your pattern.
I remember when I first found out you could alter an existing pattern in Illustrator I was very excited. So, hopefully this little quick tip helps some of you out there.