I spent around 6 hours stamping bleach onto this t-shirt on Wednesday. It was an op-shop find originally that had a slight but large fade (maybe from the sun) mark on one arm - it was only visible if you really looked but because the fabric was a solid brown once I knew it was there it sort of jumped out at me. So I thought I'd try fading it deliberately. I assembled an assortment of plastic lids of various sizes (vegemite jar, coffee jar, mouthwash bottle, toothpaste tube etc) and sanded the edges on a sheet of sandpaper so they were smooth, level and had a bit of "tooth" for the bleach to cling to. I opened several windows in case the bleach fumes got too much for me. I put some old sheeting on the ironing board and between the back/front of the t-shirt. I poured a small amount of neat bleach onto a sponge sitting on a plate so I had a stamping pad. Then I smoothed a small area of the t-shirt and stamped a few circles. I waited a minute or two until they were the colour I wanted and then dried the bleach with the iron. I did small areas at a time.
The bleach fumes weren't a problem - I used a lot less bleach than would be used to clean benches, floors etc so the fumes were minimal. Once I had finished I rinsed the t-shirt by hand in cold water, then rinsed in water to which I had added a product intended to remove chlorine from tap water to use in fish aquariums as this was a tip I had read somewhere and I thought it sounded "sensible". Then I washed the t-shirt in the normal way with the next load of clothes. The circles aren't visible on the inside of the t-shirt so I doubt very much that the entire thickness of the fabric has been affected by the bleach - I'll let you know if the whole thing falls apart while I'm in the middle of the supermarket or something :-)