The trick is getting the iron to just the right temperature. Trial and error is sometimes the only way, but I find it's somewhere in the polyester area. I have a sharpy mark on my iron to note where it is. Also, it takes a lot of pressure and a little bit of time. I also fill a ziplock with ice cubes and I shock the metal/transfer cold when I'm satisfied I've got the toner onto the metal. Like many of these methods in the forum, they're not really time efficient, but for one-offs it works quite well.
