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Chemical blackening of metal surfaces

Shiny metals are scarse in the hard day to day practise of railroading. Glittering wheels or pantographs can disturb the visual appearance of your models. So very often there is need to tone them down by making them black. Painting is usually not an option as the objects will usually not only loose their metal appearance, equally disturbing the looks, but will also disturb the current collecting function of the parts. A better way of getting shiny metal black is an electroytical treatment called anodising. This is the common way suppliers of model railroad equipment turn parts black. This method is not so easy for mere mortal model railroaders though. A better accessible method is chemical blackening.

In chemical blackening a chemical solution (duh) is used to treat the metal surface. The surface does not loose its electrical conductivity and it retains its metal appearance. Moreover, moving joins are not impeded. Various metals react differently to chemicals so there are different solutions (literally) for various metals. Above I have pictured the quartet I have and which suffice for almost modelling needs. A bottle will last for years.


Some words of caution: these are serious chemicals and you should treat them accordingly.

  • Wash your hands after use.
  • Rinse tools and containers carefully.
  • Clean up your desk before working with them and after working with them.
  • Make sure that the chemicals do not come into contact with any other metals than the objects that need to be blackened.
  • Do not mix them with other chemicals especially acids. You simply can't tell what will happen.
  • If you or a member of your household swallows it, see a doctor immediately. Do not provoke vomiting without consulting a doctor first.
  • If you get it in your eyes, rinse with water immediately and abundantly and see a doctor.
  • Keep your pets away, especially birds a have a habit of drinking from small containers with water. Remove spills immediately!
  • Chemicals should be disposed of in the correct way according to local regulations.


Dangerous? No, not when handeled with care. I could make a very similar list for working with a hobby knife. Yet, everyone knows that a knife handled with apropriate caution it is a good tool. I only mention this list of rules to make you aware that chemicals need the same amount of caution.


That said, how to work? Well, first degrease the object thoroughly. Wash it with dish washing soap and rinse. Then have it in acetic acid (household vinegar = 8% acetic acid) for half an hour and rinse thoroughly.

Put your object in a plastic container. Add distilled or demineralised water. Do not use tap water as this contains all kinds of chemicals that may disturb the action of the blackening chemicals. Add a few drops of the appropriate blackener. A few drops will do as the bottles contain very concentrated solutions, far too strong for direct operation! Let it work for a night. Remove it from the solution, rinse with tap water and dry. Inspect to see if enough blackening has taken place and if necessary repeat the process. Remember that blackening does not stop immediatetely after rinsing. The black metal surface is a little roughened and still contains a little amount of blackener. The black colour will deepen in the days following the treatment.


  • The metal did blacken but not enough. Add a few more drops of the same blackener and let it soak for another 12 hours.
  • The black layer does not adhere to the metal, you can wipe it off. You made the solution probably too strong. A novice error. Dilute the solution and try again.
  • The metal does not turn black but reddish or brown. You did not choose the right blackener. Clean and try again. In general it is a good thing to choose your most likely blackener and try it out on a inconspicuous spot of your object.
  • The blackening is not even, there are blank spots. You probably did not degrease the object enough. Degrease it again and more thoroughly and redo the blackening.

An example

A friend of mine turned up a pantograph remarking that he wanted to swap it for a darker one. I offered to blacken it.

First I needed to know what kind of metal I had at hand. Well it was obviously not brass neither solder, so two blackeners could be eliminated. I tried steel blackener on a hidden spot but I had no response. It did react to nickel silver blackener so I prepared a bath with the latter. After degreasing the pantograph I dunked it in its bath and let it stand for a night.


I added about 1,5 ml to this solution. Quite enough


The next morning I cleaned, degreased it again and let stand let it soak for another six hours. This is the result