To subject the surface of a synthetic substance to etching, activation, cleaning treatment with a promotor optionally, and metal plating by chemical reduction and/or, in succession, by electrolysis.

The etching and activation of a synthetic substance substrate are performed by a common operation stage in a first solution comprising at least one inorganic acid-containing etching reagent and an ionogen activator. The etching and activation of the synthetic substance substrate are simultaneously performed in a solution comprising one or more etching reagents, an etching activation wetting agent, and a hydrochloric acid, and noble metal ion-containing activator.