Interesting technique. Experimenting with custom brushes could lead to better looking results.

Quote Originally Posted by Karro View Post
We select the black first then invert because if we tried to select one of the white regions with the wand tool, we'd miss several of the other white regions when we perform the Stroke action next.
There's no need for this: GIMP has a selection tool that will select all areas of same color. It's the next one to the right from the wand tool on the toolbox. Just click on any white area with this tool and you'll have every white pixel selected.