I have not seen this type of grip with twisted wire applied in a diamond pattern over a leather wrap.
The ones I've seen, have the wire applied in a simple spiral pattern.
The book "The Master Bladesmith- Advanced studies in steel " by Jim Hrisoulas has a chapter where he describes how to make this grip in detail. The ends of twisted wire are not soldered, but tucked into holes on the ends of the wooden core. Bolsters of sheet metal are then press fit over the grip ends.
You can't solder metal after it's applied to wood, horn or leather. When I make a knife hilt, all the metal filligree work is done first. The wooden handle is fitted to the metal parts and attached with rivets or glue.
Best regards
Rolfkt