If you have not already read Máirín's nice tutorial about Grungy Brushes, published recently on the Red Hat Magazine, go and read it now before continue reading this. I skip here a lot of steps and present only part of the workflow.
I will explore a more simplified (and probably not that good looking) way to do it, using only vector graphics for path generation.
- Fire Inkscape, of course, this is the tool we will use
- Draw a rectangle, al large as you want. I made it red only for visual feedback in the next step.
- Switch to the calligraphic tool and draw randomly until you cover the rectangle but leave a lot of gaps, we will use only the gaps. Make sure you have one single path, otherwise select the paths and do a union (Path > Union).
- Select the the chaotic path and the rectangle and perform a difference (Path > Difference). After that break it (Path > Break Apart).
- Optionally, if the blobs are too big make them smaller using inset (Path > Inset) and if they are too complex simplify (Path > Simplify).
- Now, just as Máirín did, use the Align and Distribute dialog to move them around.
- And go wild with a lot of crazy shapes:
- As shown in the tutorial, export as PNG, import into GIMP, flatten image, convert to grayscale and save as brush (.gbr).
I think at another possible approach which would not use a rectangle and difference, but the bucket fill from the Inkscape development branch, but for now I will limit to tips and tricks about the stable version.
If you didn't read the tutorial before, I hope I got you interested, so go read it now!