In article , Winston
writes
Hi all,

I want to build up a magnetic core using a few hundred feet of 0.023"
diameter ER70-S6 MIG filler wire. To limit eddy current, I need to make
the wire non-conductive to low voltage (ca. 5.0V AC @ 60Hz) up to 100
degrees F (38 C).
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.

--
Chris Holford