Black Oxide Finish: The Complete Guide

In this guide, you will find all information about black oxide finish. It will help you choose best materials, applications, checking quality and best material to coat. So, before starting your next black oxide finishing operations, read this guide.

What Is Black Oxide Finished?

A black oxide finish is a surface finish where a metal undergoes a chemical coating process in iron oxide.  The process protects the surface from corrosion, improves the aesthetics of the surface, or even reduces the metal’s light reflection.

Hot Black Oxide

Hot black oxide is a process of coating parts by immersing them in a boiling aqueous solution of salts.  This type of black oxide coating accommodates the highest temperatures compared to all the other black oxides. In short, the procedure involves submerging the material into an oxidizing salt bath at a very high temperature.

Performing this procedure requires the expertise of a well-trained company and personnel. The whole process of hot oxide coating involves cleaning the part, water rinsing it, pickling, rinsing in the water again. Thereafter, black oxidizing, water rinsing again, drying, and then lastly treating it. This process is also known as hot blackening.

Hot Black Oxide
Mid-Temperature Black Oxide

Mid-Temperature Black Oxide

Mild temperature black oxide has the same technique as hot black oxide. The only difference is the temperature at which the part blackens. It follows the same steps which include, cleaning the part, water rinsing it, pickling, rinsing in the water again, black oxidizing, water rinsing again, drying, and then lastly treating it. Mild temperature black oxide does not emit caustic fumes and this is mainly due to it being below its boiling point.

Cold Black Oxide

The cold black oxide process is almost similar to the hot black oxide procedure but only differs where the temperatures are involved. Normally, the cold black oxide coating can take place at room temperatures. Furthermore, the cold black oxide process does not include the oxide conversion.

The cold black oxide procedure uses deposited copper selenium to coat the part. Usually, the process involves a phosphoric acid solution that has selenium and copper compounds. Additionally, the cold black oxide procedure is quite easy compared to hot black oxide, and compared to the traditional black oxide coating, this is quite soft.

Cold Black Oxide
Material Suitable For Black Oxide Coating

Material Suitable For Black Oxide Coating

The black oxide coating is commonly used on metal parts. Non-ferrous metals are most suited for the black oxide coating process but you can use the black oxide finish on ferrous metals. The following are the materials suitable for black oxide coating;

  1. Zinc
  2. Cast iron
  3. Copper
  4. Nickel
  5. Stainless steel
  6. Brass
  7. Silver solder
  8. Cadmium
  9. Copper-based alloys
  10. Powdered metals

Benefits Of Black Oxide Coating

Benefits Of Black Oxide Coating
Benefits Of Black Oxide Coating

Black oxide coating involves adding a layer to a part to protect it and to add to it some properties. The following is a list of benefits of black oxide coating;

  • Black oxide coating protects the material from corrosion. Some metals attract rust when they come into contact with water so coating them with black oxide prevents the rust.
  • It improves the aesthetics of the metal. Some metals are plain and bare but when the coating is added to them they become more appealing and beautiful.
  • Black oxide reduces the metal’s light reflection. Some products are completely affected by light reflection affecting their results. The black oxide coating completely minimizes the light reflection.
  • Black oxide coating can also add to the thickness of the metal. Adding to the metal’s thickness also increases its strength.
  • Through the coating, things like screwdrivers maintain their sharpness. This is an important factor since the sharpness of such things is very essential. Some coatings can reduce the sharpness of metal hence reducing their effectiveness.
  • It helps reduce friction. The black oxide coating includes either oil or wax which minimizes friction or even removes friction completely.
  • Black oxide coating gives the metal water-resisting properties. This is a very important factor since water can lead to rust. The oil or wax in it is the reason for the water resisting property.
  • Black oxide coating helps increase the lifespan of metal. It is corrosion resistant as well as water resistant and because of this, it can last very long.

Black Oxide Finish Process

Black Oxide Finish Process
Black Oxide Finish Process

The black oxide finishing process involves five major steps. Some of these steps include cleaning, rinsing, black oxide application, rinsing again, and finally after-finish treatment. There are some additional processes such as pickling and alkaline descaling.  You should include these processes if the parts to be finished have rust on them.

There are different types of black oxide finishing processes and they all have different formulations.  They follow the same steps but they have different temperature tolerances. Additionally, the hot black oxide process and the mild temperature have the same technique, the difference is the temperature at which blackening is done.

Normally, the hot black oxide finish process is done at high temperatures but the cold black oxide finish requires room temperature. Furthermore, the cold black oxide process does not include the oxide conversion.

Again, the cold black oxide procedure uses deposited copper selenium to coat the part. The process involves a phosphoric acid solution that has selenium and copper compounds. For the hot black oxide finish, the procedure involves submerging the material into an oxidizing salt bath at a very high temperature. Below is a detailed explanation of the black oxide finish process;

  • Cleaning – clean the part in an alkaline solution to degrease it and ensure it is free from any contamination
  • First rinsing – rinse the cleaned part with distilled water
  • Pickling – you only pass the part through this step if it has rust. You use acid to clean the part to remove the rust.
  • Second rinsing – after removing the rust or any stains you clean the part with distilled water again.

Only do the second rinsing if the parts have gone through pickling.

  • Black oxidizing – this is the main process. It involves submerging the part in hot alkaline for about 5 to 40 minutes.
  • Final rinsing – here you use a pressurized water stream to clean the part after the black oxidizing step.
  • You then dry the part, then do an after-finish treatment. The after-finish treatment is an essential part of the whole process. This is because it will improve the aesthetics of the part and add to its corrosion resistance properties.  You can either finish with wax or oil depending on the type of appearance you want.  An oil finish will give the part a glossy finish while a wax finish will give it a matte finish.

Factors To Consider When Choosing Black Oxide Finish

Factors To Consider When Choosing Black Oxide Finish
Factors To Consider When Choosing Black Oxide Finish

Before choosing any product or service, there are certain considerations you have to look into. By doing so you can get the best of what you are looking for. Listed below are the factors to consider before choosing a black oxide finish;

Where to you use the part – different industries use products that have a black oxide finish. So, you need to know where you will utilize the product. On the good side products with a black oxide finish is so versatile meaning you can use them in any industry without any issues.  This means you do not need to stress where you will use the part.

Type of finished part appearance – after the part has gone through all the black oxide finishing process an after-finish is added to it. The after-finish can either have wax or oil in it and they give different results. An oil finish will result in a glossy finish while a wax finish will result in a matte finish.

Longevity of protection – when choosing a black oxide finish, the common question is how long you want the part to last.  A black oxide finish is one of the best finishes when it comes to surface protection.  Though the period of protection might be affected by several factors, it is still one of the best.

The price of the black oxide finish – before choosing any part, you should make sure its price is within your budget.  You should avoid overspending but also ensure the service you get is worth your money’s worth. You can check with different service providers to ensure you get the best quality at a good price.

Limitations Of Black Oxide Coating

Limitations Of Black Oxide Coating
Limitations Of Black Oxide Coating

There are always benefits and limitations to anything. These are the limitations of black oxide coating;

  • In high temperatures, the black oxide coating can wear off easily. This is quite often on products that have gone through the hot black oxide process.
  • Black oxide coating involves a lot of steps. The black residue may come off the fasteners hence requiring wiping down.
  • It is quite easy to rub off a black oxide coat. They require some additional steps to ensure it does not rub off.
  • Black oxide does not offer very high corrosion resistance. This doesn’t mean it does not protect rather it means there is no maximum protection and the part can eventually rust.

Testing Quality Of Black Oxide Finish

Smut Test

You should do this test before the after finishing treatment. It is a black residue test to see if the black coating can come off when you wipe it or if there is any powder residue on the surface.

Relative Humidity Test
Relative Humidity Test

This is a test to check the corrosion resistance ability of the finish. It tests the water resistance of the part that has undergone black oxide finishing in 100% relative humidity.

Visual Test
Visual Test

This is a visual test to see the outward appearance of the finished part. Its main aim is to ensure you have completely covered the part in black. Pre-existing parts deformities should remain the same.

Application Of Black Oxide Finish

Automotive Industry
Automotive Industry

Parts like cans for oil filters and under-the-hood fasteners use the black oxide finish

Medical Industry
Medical Industry

In the medical industry, equipment that is in conditions that are light sensitive use the black oxide finish since it minimizes light reflection.

Military
Military

In the military, you can use the black oxide finish on shotgun shell magazines and gun components.

Electrical Components
Electrical Components

You can use black oxide finish on electrical components such as wire strippers, electrical switches, cutters, and gears for timers.

Hardware Tools
Hardware Tools

There are several tools like bearings, fasteners, springs, shafts, cutting tools, and many more that you can use to assemble parts. Most of these parts are finished using a black oxide finish.

Household And Garden Tools
Household And Garden Tools

Tools such as clipping tools and tree toppers use the black oxide finish.

People Also Ask:

Do Black Oxide Finish Rust?

One of the reasons a black oxide finish is added to a part is because it can be able to make the part resistant to corrosion. Although, there are some instances in which the part can rust even with the black oxide finish.

Is Stainless Steel Better Than Black Oxide?

This might be quite a challenging question since both stainless steel and black oxide have their pros and cons. Black oxide offers a matte look that is less reflective than stainless steel. Additionally, the black oxide coating also gives the part a better grip than stainless steel which is smooth and slippery.

Will Black Oxide Affect Surface Finish?

No, black oxide does not affect the surface of a part. The part will remain the same and there will be no alterations.  If the part had some deformities, it will remain the same and also the surface finish will remain the same.

Can You Restore Black Oxide Finish?

Yes, you can restore a black oxide finish. If you have the desired finish look you can choose one and apply it.  There is a wide range of ways you can restore it.

Is Black Oxide Finish Shiny?

Black oxide finish can either be shiny or matte depending on the after-finish treatment you apply. You can either use oil which results in a shiny surface, or wax which results in a matte look.  Black oxide finish will not change the surface finish, it will remain the same only the color will change.

Is Black Oxide Same As Plating?

Black oxide and plating are not the same. Plating involves adding a layer of metal to the part while black oxide is coating the material in iron oxide.

Is Black Oxide Finish Safe?

Black oxide finish is not safe, it requires a skilled person to handle the process. Some harmful chemicals are hazardous to people as well as the environment.

Related Resources:

Metal Finish

Black Oxide

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