The varnish I used is intended for oven-drying at 140 to 150 degrees Celsius. I don't have an oven large enough to fit this coil, so I heated it by applying roughly 20A of direct current to the high voltage winding. I monitored the temperature by measuring the resistance change of the wire.
If you know the temperature coefficient of the wire, this isn't particularly hard to do! You can do it easily by applying a constant voltage roughly of the wanted amperage and then calculating the resistance via voltage and resulting amperage, then feedback to adjust voltage.
It's fairly popular in a wide range of applications, mostly either machines with too much current or too large areas to reasonably measure temperature or parts that are too small (vape coils for example can be used in a temperature coefficient mode).
I can't even...