What is blackened steel?

The industrial and stylish look of blackened metal can lead to strikingly distinct contemporary architectural pieces and machine parts. But, metal blackening does not necessarily only mean black. Depending on the process used to blacken the metal, a wide array of colours are possible. Plus, in addition to the aesthetic effects, metal blackening can also improve resistance to corrosion and general wear and tear. With so many different processes that can be used to blacken metal, it can be difficult to know which one is best for your project. This article will explain metal blackening, the different processes used to blacken metal (particularly steel), and the benefits of each.

What are metal blackening and blackened steel?

Metal blackening is the process by which the surface of a metal part is coloured black – whether by chemical reactions or by painting/waxing. The specific process determines the colour of the metal – ranging from light grey to jet black. Metal blackening is typically used to enhance appearance, minimise the reflection of light, and give some resistance to corrosion and wear-and-tear. So, blackened steel is simply steel that has undergone a metal blackening process.

Types of metal blackening processes

Below are some examples of common metal blackening processes:

1) Painting and waxing

Using black paint on metals gives the illusion of chemically treated blackened metal but is accomplished without the chemical processes associated with plating. Like any other painting project, the surface of the part must first be cleaned to prevent any foreign debris from sticking to the surface. Painted metal can have a matte or glossy appearance, and can be done on smooth or textured surfaces. Additionally, using paint is a good way to hide unsightly features like riveted or welded joints. Both wet and spray-type paints offer good corrosion resistance. All this makes painting a cost-effective, economical alternative to plating processes while still achieving beautiful blackened steel finishes within short lead times.

Similarly, no chemical processes are needed when using wax to blacken metals. To use wax to blacken steel, the part must first be heated to approximately 204℃. Then the part is covered in a mixture of wax and oil, resulting in a blackened part with a consistent finish that lasts a long time without significant wear or changes in colour. This makes wax an excellent choice for parts that see a lot of traffic.

2) Chemical conversion (plating)

Chemical conversion processes, otherwise known as plating, involve applying thin layers of metals (like zinc, chromium, or nickel) onto the surface of a substrate metal. The result is a metal part with added resistance to chemical damage and corrosion as well as improved durability and resistance to normal wear and tear. 

There are several different metal plating processes. These include zinc coating (galvanising) and anodising, to name a few. Zinc coating is typically used for steel and is accomplished by dipping the part in a molten pool of zinc for “hot-dip galvanising.” This leaves the steel with a silvery colour. On the other hand, anodising is similar to a different method of galvanising called electro galvanising. But anodising, does not add a layer of new metal. Instead, it involves dipping an aluminium part in a bath of either sulfuric or chromic acid. Through a series of electrochemical reactions, the part is anodised and will be better able to resist corrosion.

While metal plating has the ability to improve certain properties of a metal part, like paint, it can also enhance the overall appearance of the part. Metal plating can be a complex and intensive chemical process that involves more investment and more labour, but its cost can be justified for both small and large batches of parts.

3) Black oxide conversion

Black oxide conversion is a type of plating process but deserves its own section due to its critical relationship with blackened steel. The process is more similar to anodising than galvanising in that the part’s dimensions do not change.  Black oxide conversion involves taking a metal part (typically steel) and immersing it in an alkaline steel blackening solution. The result is a durable coating that will resist colour fading and will not chip, peel, or flake. This makes black oxide conversion an excellent metal blackening process for precision parts that need some corrosion resistance but need to maintain their original dimensions.

Final thoughts

Metal blackening allows manufacturers to not just improve on the aesthetics of a metal part, but also to improve resistance to corrosion and general wear-and-tear. With such a wide variety of metal blackening processes, it can be difficult to know which one is right for you. Ludwick Precision gives a wide range of painting and finishing options for blackening steel such as anodising, zinc plating, and chrome plating, among others. Our team can manage the whole end-to-end process for your project. Contact a representative at Ludwick Precision today to discuss which metal blackening process is best for your design.