For me, it's (c)
No doubt you've already noticed the spirals are of flat strips of gold. Goldsmiths still make gold wire for jewellery by cutting thin strips off of a flat thin sheet of gold, with snippers. If you've ever done any metalwork like that, you'll remember how the offcut curls because of the shape of the snipper blades. Curling the offcut round a stick as you go would keep the metalwork tidy, and the end result would the the spiral shape as we see it in those pictures.
After that, you straighten out the spiral and then work it down to the diameter you want the wire to be. Seemples!
For example:
http://www.engravingschool.com/private/gold-wire.htmAnd here's a video of someone doing that:
https://www.youtube.com/watch?v=Z_w-bnDOHoc