The type of coating employed for the production of stitching wire is usually an electrolytic deposit of zinc.
However, there are alternative coatings of copper, tin or a hot dipped alloy of zinc and tin.
The essentials of a good coating are that it should be very smooth and adherent, as any loose coating quickly blocks the stitching head guides.
There is always a compromise between producing a wire which is clean enough to eliminate marking the work piece, but at the same time has sufficient residual lubrication to help the wire through the stitching head.
c) Coating Thickness
The coating offers a degree of corrosion resistance. However, too much coating leads to flaking and blocking of guides.