I know that 3D printed parts can be coated in metal by painting them with conductive paint (graphite or copper seems to be usual) and then electroplating them in a commercial copper or nickel bath. The disadvantage of this process is that it does not coat insides very well, because those are not reached by the electric field.
I know that in the industry for plating ABS-parts with chrome and other metals, there is a process used where first the ABS is etched, then seeded with electroless catalytic palladium and then there are various options, for example electroless nickel or chrome.
I tried to etch both FDM printed ABS and ABS-like resin prints in NaOH, then after rinsing, dropped them in a commercial palladium activator and, after rinsing again, then in an electroless nickel bath, without any effect.
Does anyone have an idea on how to metal plate 3D printed parts (by electroless plating, meaning no electricity involved) and can shed some light on the chemicals used? I would prefer to mix them myself.