I saw somewhere in the net a cool way to 'paint' on t-shirts : you lay objects on them, and then spray them with 50 % bleach and 50 % water until it looks good. Then quick rinse and wash. I tried on a bunch of (mostly old) shirts, and this is my favorite so far. To make the lines even stronger, I hand stitched with a contrasting yellow yarn.
More pictures of this project (lazily enough) uploaded to my Crafts folder. More to be uploaded soon!