mostly co-deposited with nickel (like the stabilizers). surfactants, to keep the deposited layer hydrophilic in order to reduce pitting and staining. accelerators, such as certain sulfur compounds, to counteract the reduction of plating rate caused by complexing agents. They are usually co-deposited and may cause discoloration. Surface activation Because of the autocatalytic character of the reaction, the surface to be plated must be activated by making it hydrophilic, then ensuring that it consists of a metal with catalytic activity. If the substrate is not made of one of those metals, then a thin layer of one of them must be deposited first, by some other process. If the substrate is a metal that is more electropositive than nickel, such as iron and aluminum, an initial nickel film will be created spontaneously by a redox reaction with the bath, such as: (s) + (aq) → (s) + (aq) 2 (s) + 3 (aq) → 3 (s) + 2 (aq) For metals that are less electropositive than nickel, such as copper, the initial nickel layer can be created by immersing a piece of a more electropositive metal, such as zinc, electrically connected to the substrate, thus creating a shorted Galvanic cell. On substrates that are not metallic but are electrically conductive, such as graphite, the initial layer can be created by briefly running an electrical current through it and the bath, as in electroplating. If the substrate is not conductive, such as ABS and other plastics, one can use an activating bath containing a noble metal salt, like palladium chloride or silver nitrate, and a suitable reducing agent. Activation is done with a weak acid etch, nickel strike, or a proprietary solution, if the substrate is non-metallic. After-plating treatment After plating, an anti-oxidation or anti-tarnish chemical coating, such as phosphate or chromate, is applied, followed by rinsing with water and dried to prevent staining. Baking may be necessary to improve the hardness and adhesion of the plating, anneal any internal stresses, and expel trapped hydrogen that may make it brittle. Variants The processes for electroless nickel-phosphorus plating can be modified by substituting cobalt for nickel, wholly or partially, with relatively little changes. Other nickel-phosphorus alloys can be created with suitable baths, such as nickel-zinc-phosphorus. Composites by codeposition Electroless nickel-phosphorus plating can produce composite materials consisting of minute solid particles embedded in the nickel-phosphorus coat. The general procedure is to suspend the particles