No it does not harden or discolor. It is just a thick starch. So when you wash your project it washes out like the starches you use to iron with. I have been using it for a few years now and it truly does just wash out of cotton fabric. I did a few test project before i went 'live' with it. I know i do have pins in my sewing room... somewhere. but my glue is right here! Try testing it out... that is the best way to get converted. remember to use a tiny amount... and then heat set it by pressing with your iron. it makes quilters magic happen! amazing stuff. Elmer's washable school glue