This tutorial, such as it is, could easily be called How to create seamless tile repeats with Gimp. If you do a google search for Gimp seamless, you will find lots of tutorials. Because of that, I won't do a detailed tutorial. This is a follow-up of my review of A Field Guide to Fabric Design.
The main difficulty I had with Gimp and creating a seamless repeat is a problem filter*.
Don't use this filter:
Filters - Map - Make Seamless
The resulting image doesn't make an attractive repeat. It overlaps the repeat with transparencies.
Instead the offset tool, which is similar to Photoshop, is located:
Layers - Transform - Offset
Finding this tool made all the difference. Conversely, I played around with the select tool and moving layers around to accomplish the same thing. The offset tool works best with the design repeat located far from the image borders and in the center of your image. For more complex repeats, manually selecting parts of the image, copy-paste into a new image and moving them in layers works better.**
I started my experiment with a vector line drawing made in Inkscape and exported as a PNG file.
Gimp has a handy tool that allows you to test your repeat located here.
Filters - Map - Small tiles
This is how my repeat looks now.
The repeat could use a bit more work, but I think you get the idea. A Field Guide to Fabric Design has information on how to improve your repeat and also how to create a whole collection around this one design.
This video demonstrates better than I can explain how to create a seamless repeat in Gimp.
Of course, the real challenge is matching up the colors with Pantone.
* I tried to take screenshots of all of this but my print screen button wasn't cooperating.
** One of these days I may create a tutorial for this, but it is a bit more involved. My trial video demo took about 20 minutes.