Feedstock is supplied in filament form — aka wire — and melted to deposit on the work piece in order to build up either welds in the case of the welder, or 3D ... a metal build plate serves ...

Like most of us, [Clem] wants to 3D print in metal ... used as a step to make a part conductive so you can then plate with another metal. In addition to copper sulfate, you can use copper acetate.