Just mix the RIT dye according to directions. For clothing & stuff it's supposed to be pretty hot. For tinting clear plastic parts, I let it cool some. I usually dip a piece of scrap to make sure it's not too hot. When the temp's OK, dip the part in for a minute or so, pull it out & see if it's as dark as you want it. If not, dip it again & as many times as needed. When you get it the shade you want, rinse it in water & let it dry. It's done. I've done some canopies before as well as tinting some 6" clear styrene domes for some Major Matt Mason scratchbuilt space vehicles I've done. Just remember, it's easier to make it darker if it's too light, but once it's too dark, it can't be reversed.