The first photo shows the coil of Litz wire and the two end protruding out from under the Alnico magnet. The second photo shows the same pickup after wax "potting".

This is actually my second pickup having this design. I have my first in one of my guitars (the first guitar I built), and I'm "trying it out". The signal is a little weak and treble, since I have to turn my amp up almost to half to get a good loud sound. The treble is not too bad, but it is excessive - no one would want it like that. So, in this second attempt I have used wax potting and a metal case. I expect it will be better. How much better, we shall see.

Hmmm, I guess if it is wax potted it is not an "air coil", but a "wax coil".

I've received the Litz wire that I'd ordered. I haven't decided exactly what experiment I want to perform. Time will tell. https://www.electronics-tutorials.ws/inductor/parallel-inductors.html

What is the configuration - strands and gauge?

I've just assembled and tested my second functioning pickup - and it is much like the first, only the signal is somewhat more powerful. This is with 500 winds of 7/44 gauge. It's taking more wire than I expected. I think I will jump to trying a 20/44 configuration.

Litz Wire, 24 AWG Unserved Single Build, 25/38 Stranding, 2 oz Spool, 100 feet

Heavy Duty! 😀