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Bluing is a metal finishing process that provides some protection from corrosion. In this process, manufacturers and metalworkers create a thin layer of iron oxide on the surface of steel products. This limits opportunities for corrosion and keeps the steel in good condition, although it may require regular oiling and other maintenance. Bluing can be used on weapons, tools, and other steel products. It does not work with metals that do not contain iron, as the necessary chemical reaction cannot occur.
Several techniques are in widespread use. These include cold processes where technicians spread compounds on the steel, hot bluing, and fuming or rust bluing, which facilitates the slow development of a layer of iron oxide. Cold methods are the least effective, while fuming yields high quality results but can be time consuming and expensive, which tends to make it less desirable, except for costly equipment that may benefit from the extra protection.
All of these processes trigger the controlled oxidation of the metal. This chemical reaction facilitates the formation of iron oxide, which will gradually spread across the surface of the metal and create an extremely thin layer of material. The underlying steel should remain in good condition as long as the surface is well kept. Hardness and other characteristics are dependent on the manufacturing processes used to make the steel, and can vary between products.
As the name suggests, bluing adds a faint blue tint to the finished product. In addition to protecting the steel from corrosion, it can resist some scratches and surface abrasions. Regular cleaning and oiling help keep the surface looking clean and even. Maintenance of the finish is important, as once the iron oxide starts to scratch or flake, the underlying metal can be vulnerable to rust. It is also possible to remove bluing, if the finish is not desirable.
Firms that use bluing in their processing may offer several finishes to their customers. People can choose unfinished metal if they want to apply finishes on their own, or can select between several oxidized coatings. It is also possible to send equipment out for maintenance and restoration to remove and replace the finish if it becomes worn and less effective. Some companies specialize in the handling of antiques and other unique items that may require extra care in the refinishing process.
Home bluing kits are available for people who want to finish steel parts at home or restore equipment that needs a new finish. It is important to work with clean equipment at all times, and to control the process carefully to get the desired effect. Once a finish has been applied, regular maintenance can help it last longer.