A method for forming a metallic mirror surface on a receiving surface is shown. The method comprises the steps of: cleaning the underlay surface; spraying on the receiving surface an activating treatment agent solution wherein the activating treatment agent solution contains a hydrochloric acid solution including about 10 cc to about 44 cc of hydrochloric acid, about 1.5 g to about 5 g of stannous chloride and about 0.001 g to about 0.005 g of a precious metal salt of at least one of a silver nitrate, palladium chloride, gold chloride and platinum chloride per 1 liter of water for use as an activating treatment agent for forming a metallic mirror surface on a receiving surface which is treated with the hydrochloric acid solution as an activating treatment agent solution; and separately spraying concurrently on the underlay surface a reacting metal salt and a reducing agent to form the metallic mirror surface.