In article , Winston writes
Snip
I suspect that the insulating coating doesn't have to be perfect. Just a thin layer of oxide would do the trick -after all the contact area between the bundled wires is quite small. I noticed in the 'JP Transformer' book that someone kindly posted the URL for that one method used was to phosphate coat the iron. So just use one of the phosphoric acid 'rust treatments' to give a thin coat of phosphate.