Been meaning to try this for ages. Here's what happens if you hang a damp top over the bath and squirt bleach at it with a syringe:
Hoping I'll wear these a bit more now they're more interesting, and I've strategically aimed the bleach at a couple of stains that wouldn't come out any other way, so they don't look so grubby now either.
I think that if the fabric is dripping wet and the bleach solution weak then it runs more and you get a more blended, patchy effect, which is more subtle. Dryer fabric and neat bleach gives bolder shapes with sharper outlines. With this in mind I think next time I'll use a weak solution to make the colour patchy as a background, and then rinse, let it all dry completely, and use neat bleach to make more precise patterns over that.
One word of warning - gloves. I almost never wear protective gloves because I hate how they feel, but after rinsing these tops out my hands are distinctly sore and I wish I had.
What I forgot to take a photo of was the bathroom wall - luckily tiled - splattered dramatically with the red fabric dye that I also used on the orange one when the bleach didn't show up as much as I wanted. And the syringe full of red liquid on the side of the bath. Thank god no one called round just then.