It's probably worth lining up a fw pieces of card to do at once. Again, here I have done it in contrasting colours to show you more clearly, but it looks lovely in different shades of the same colour too.
I actually prefer this done with thread, as you get more delicate lines, but I've used string in the video to make it clearer.
I have popped a tiny bit of double sided tape at the end of each roller to keep the thread attached. If using fine thread, I use an ink pad, if I'm using string, I use paint as in the video. Another popular thing to do along the same lines as this (no pun intended!!!) is to wrap rubber bands arond your brayer.
I have used contrasting colours here to show you, but the effect looks really nice using shades similar to the background.
You can use your brayer to blend lovely backgrounds with paint. I have used Luna Lights here, but you can use any acrylic paint. The swirls stamp is from Paper Artsy. Scroll down for a video on how to do this.