The Process

The Process

First of all the most important: For the whole blacking process and the later quality of the blacked components the accurate pre-treatment is essential. 


Ensure components are adequately degreased and free of scale, oxide and other contaminate. Only metallic and chemically pure surfaces guarantee a high quality result. If the surfaces are contaminated by oil or emulsion you will not achieve a good return.

For the treatment of difficult or extremely oil contaminated parts it may be necessary to degrease them with our NU-BLAK® No. 626 hot degreaser at 80°C. Other methods like electrochemical degreasing, ultrasonic or acid pickle are also possible.

Unquestioned the best pre-treatment is sand blasting or to blast with glass or diamond etc.- provided that the surfaces are qualified for (except for fitting parts!).

A special note for case-hardened objects. They are often covered by a cured coat and require a special treatment to avoid problems (sand blasting, acid pickling, hot degreasing etc.).

Intermediate Treatment

After each step – except for dewatering – rinse the components adequately to prevent carryover contamination and product wastage. Our highly efficient filtration system in a closed circuit enables an economically water consumption. The contamination of the waste water is very low and in any case below the limit values.


To reduce the pH-value it is recommended to apply our Conditioner NU-Blak® No. 551.For some specific processes – like sand blasting for example – the conditioning is not necessary. In no case using the conditioner is harmful and part of the standard process sequence.

Main Treatment

At this point our NU-BLAK® No. 181 Blackener comes into operation. Immersing of the pre-treated parts in a solution consisting 1 part of blackener and 3 parts of water for max. 1 minute will start the blacking process.

The duration of the blacking process depends on the temperature of the blackener and the characteristics of the base material. The temperature of the blackener is important. Above 22°C the process takes about 30 seconds. Below 22°C the blacking will take a little longer. Accurate blacking at a temperature less than 16°C is not possible!

Dewatering – Oiling – Sealing

Conventionally the parts (without after treatment by cold corrosion preventative) are cured with hot air or in oven at 120°C.

Using our dewatering oils a drying in oven is no more necessary. The water based corrosion preventatives will dewater the capillaries of the surface. The immediate effect is a corrosion protection reached by air drying.

Different options are available:

NU-BLAK® 833 M


a medium viscous oil for permanent corrosion protection

NU-BLAK® 841 H


a viscous oil for improved corrosion protection

NU-BLAK® 925


A sealer, mixable and water based, commonly used where surfaces free of oil are required (like in sorting plants etc.)

and a synthetic resin sealer is available for immersion or spray.

After drying period a resistant to corrosion coat remains. Dry-mat with NU-BLAK® No. 925 or light-oily with NU-BLAK® 833 M and NU-BLAK® 841 H. 

Diagram of the blacking process using our NU-BLAK® Cold Blacking system:

A typical line would be configured as follows:

Additional informations: Arrangement for the safe and improved handling of small plants with different chemicals:

The following modification will considerably improve the efficiency of the system: 

Tank No. 1 –> Cold Degreaser NU-BLAK® 716

The degreasing will be more effective while the liquids are in motion. You can achieve this by using a simple, corrosion resistant pump. Air pressure techniques are unqualified because of the production of high quantities of soapily foam.

Suitable conditions you can also reach by using methods like ultra-sonic, vibration or pneumatically mixers. 

It is recommended to heat the degreaser solution by immersion heaters or heat mats. This will increase the quality and the flow rate. It is important to keep the solution at a temperature of min. 20°C. A temperature of about 30°C for example will accelerate proceedings significant. A temperature control strip is included. To ensure a constant temperature especially in the wintertime an external heater beneath the tank is a good choice. Using inoxydable steel tank instead of the plastic tank you will need a hotplate or an immersion heater to reach higher temperatures. 

Longer immersion times will improve the degreasing results as well. 20 minutes are a good standard value. To achieve better results and reduce the consumption of chemicals the components should be cleaned separately. Never apply a cleaner containing ingredients like phosphates or acids for the pre-treatment.

alternative / additional:

Tank No. 1 –> Hot degreaser NU-BLAK® 626

Inside of a inox-tank the temperature should held at 80°C (by immersion heater and thermostat). This will reduce the time of the treatment and increase the quality of the degreasing in any case. Longer immersion times improve the quality. In this connection 10 minutes are a standard value. 

Tank No. 2 – 4 – 6 –> Water for rinsing

The adequate rinsing with crystal clear water is very important. Incoming water should be directed to the bottom of the tank to avoid foam formation.

Either using our filter system with a closed circuit or add fresh water continuous. In this case apply the overfall to discharge the used rinsing water to sewer.

Another improvement of the rinsing process you can reach by setting the bath in motion by aerate oil free compressed-air through a perforated pipe in the tank. 

Tank No. 3 –> Conditioner NU-BLAK® 551

Manual movement will assist the already short conditioning procedure – for larger components supported by a corrosion resistance pump. The treatment time for the conditioning takes between 30 seconds and 1 minute.

Note: This step is not recommended for the treatment of material 1020-4140-1018, HSS, ground surfaces and hard metals.

Tank No. 5 –> Blackener NU-BLAK® 181

Keep the solution temperature at room temperature (about 20° C). Especially in the wintertime you can reach this with the supplied warming mats or a warming bath. The provided control strip allows monitoring the temperature.

The treatment of higher quantities require uninterrupted filtration. The filter will remove depositions of iron-phosphate. The best results you will achieve with our filter pump BFB and/or with one of our filter plants (vide equipment). For the best results additional airflow circulates the blackener. This avoids sedimentation and will remove carryover. 

Foam formation and contamination of the blackener you can remove with our coal filter plant. It is important to apply this filter medium only sometimes when it is necessary. In no case install this filter permanent!

Application time: 30 seconds to 1 minute is a standard value (a warmer bath gives a faster reaction)

Tank No. 7 –> Hot water for rinsing (optional)

Such a tank is suitable to heat up to about 80°C with an immersion heater for example. Immersion components after the blacking process for about 1 minute. The effect is a reduction of the immersion time in the dewatering oil from 20 to ca. 5 minutes and the time to air dry form 45 to ca. 10 minutes.

Tank No. 8 –> Dewatering oil NU-BLAK® 833 M or NU-BLAK® 841 H

Normally the oil No. 833 M is absolutely sufficient. Only if a very high corrosion resistance is required the oil No. 841 H is the better choice.

While the dewatering process water concentrates on the bottom. Using our plants with water collection features to drain the water through a tap or positioning the parts on a metal sheet to avoid direct contact to the water. You can also work with our water based sealers No. 925. 

Additional Information

  • For complete immersion and the possibility of movement it is recommended to keep up the filling quantity. 
  • All tanks should be equipped with tights-fitting lids.
  • Attention should be paid to the concentration of the bath. Keep concentrates ready for refreshing.
  • Blacking the components separately or place them on a rack for the best results.
  • Usage of charging baskets depends on the nature of the parts – in any case you have to prevent carry over.
  • For the treatment with oil a separate charging basket is recommended!

Please take also notice of our manuals, application and safety data sheets and our trouble shooting guide.