Koftgari, How is it done?

[Jeff Pringle]

Had it been foil, there would not have been so much left in the middle of the crosses, as the foil will be equally thick all over, but the wire would be thicker in the middle.

Good point, I agree.
I was trying to imagine the whole surface covered in larger pieces of foil, with the design scraped through, but everything seems to point more toward wire, which is the common way of building up designs on these swords anyway.

There, the silver has nearly all gone, but the hilt appears to be covered in an undulating pattern, the high parts where the silver was, and furrows between.

Usually, there is some attempt to erase the crosshatching where it is not holding silver on the surface, more or less effective depending on the craftsmanship. That, plus some rust are more likely than an acid treatment.
Jeff