I was never able to find the welding rods that John says to use in his coil design so I have cut up coat hangers in there and they work just fine. What I need to know is, are there any core materials that I can use that are not magnetic but will still have the same effect as a full metal core? The issue is that an air core is nowhere near as strong as a metal core, and I do not want the magnets to be attracted to my core while still retaining the power of a metal core vs an air core. Anyone know this?