Arrowroot MAY work, but maybe not. It's more for paper, vs canvas. People use gelatin as well for coating paper for photographic work.
Are you using raw, unprimed canvas? That is traditionally coated w/ rabbit skin glue in several coats. The canvas will need to be stretched onto stretcher bars first, just like a painting would, or it will get all wrinkly and uneven if it is brushed w/ any liquid and then allowed to dry on its own w/o some sort of support. Or you could stretch it over some sort of flat board like surface. It will shrink when it gets wet and dries, so it has to be stapled down well all around. I prefer to use ready mixed white gesso from an art supply store and save some poor rabbits lives. You theoretically could use a good latex polymer paint instead for your project. That could be bought from a hardware store and would be cheaper. Anything that comes from an art supply store costs the mint. If you don't care about permanency, any old latex paint will do.The really neat thing about canvas stretched onto stretcher bars is you that don't need to frame it. You simply hang it on the wall and it looks great.
The easiest thing would be to buy some primed canvas. Even Walmart sells them primed and already stretched onto stretcher bars. Kevin is correct when he said that the sensitizer soaked into the canvas, giving you a much weaker image. It also may eat up or stain the canvas over time. You want to have whatever you apply to canvas sit on top of it, not soak into it, unless you are using acrylic, water based ink or watercoulor paints.
Thanks
