Bluing: hot and cold bluing processes

Bluing for metals: excellent non-stick and chemical resistance

Bluing is a particular chemical treatment used to blacken objects made of iron, steel, brass and aluminium, yielding a darker surface colour that tends towards bluish black. The treatment is used to improve the appearance of the metal and guarantee non-stick properties and corrosion protection. Bluing can be carried out either hot or cold. Let’s learn about the two different processes.

Cold bluing: safe and ecological

Cold bluing is an easy way to obtain the desired treatment. It is inexpensive, respects the environment and does not require any particular experience. It is suitable for materials such as iron, copper, zinc, brass, steel and bronze and relies on a chemical conversion process to generate a black oxide that forms a layer of metal up to 3 microns thick. This is therefore a negligible thickness that does not change the size of the object, ensuring a uniform colour over the entire surface.

Hot bluing

This bluing method consists in immersing the metal in boiling water with the addition of substances such as copper sulphate, lead acetate and sodium hyposulphite. Over time, the colour takes on different shades, from blue to grey to black. Once extracted from the water, the object is left to cool to room temperature.

Alternative solutions to bluing (technologically more advanced) also exist, such as the polymer and fluoropolymer coatings of Impreglon’s TempCoat® system (including those in Teflon PTFE, FEP and PFA). These lend the surfaces non-stick properties, corrosion protection, and resistance to chemical agents and high temperatures.

With their characteristics, these processes can be used in industry, ensuring greater wear resistance and easier cleaning.