So I was driving by an old garage, and stopped to take some photos of the chipped, peeling paint.

Here is one:
Click image for larger version. 

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That I started with by tracing the bitmap in inkscape and moved tings around a bit, then brought the path into gimp to paint. Just playing with this technique, not sure how far I'll go with it. Most of the textures have come from genetica viewer.
Click image for larger version. 

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-Rob A>