This was inspired by an afghan I saw on the web five or six years ago. I lost the link and can’t credit the original. I think she’s a Canadian designer and shopkeeper.
There are perhaps a dozen slip-stitch patterns. Some of them are the simplest ones from Barbara Walker books, some I copied from the original blanket, and some I made up as I went along.
I cast on each square with several extra yards of the background color on the other side. I carried the border color up each side so each square was self-bordered.