I grabbed a few offcuts of various fabric types to have a play and was disappointed to find the vast majority "bled" when I used the pens directly on them. Using a black laundry pen as an outline, then colouring in, helped a little, but it wasn't as neat as I'd hoped. My drawings needed to be very small indeed in order to fit onto brooches, keyrings and bag charms ... this didn't help the situation! After a bit of a think and a couple of mugs of tea I decided to try using some offcuts of interfacing. As is typical of many crafters, I can't bear to throw anything away, so all my interfacing offcuts are kept in the crafting draw (for that special day when they'll come in handy ... like today!). Hey presto, it worked a treat. The medium interfacing is sturdier than cotton and linen and the weave very close together so there's very minimal bleeding. I'm able to draw the picture in pencil first, outline in the laundry pen and then carefully colour in. Ironing the finished drawing, with protection from a tea towel, seems to set the colours and they didn't seem to run when washed under the tap. All good to go.