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DIY Black Oxide Anodizing Steel

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DIY Black Oxide Anodizing Steel

Hi Guys, this is a new experiment I wanted to share with you, it may be useful :

I am actually on a mod project, & at some stages I had to cut a bunch of black steel screws, the problem is, after you cut steel, you loose that protective layer of black oxide applied during the manufacturing process. After a few days , if you don’t paint the parts, the cutted end, tend to rust :


Painting about a hundred of tiny hex screws is kind of boring to me,  furthermore,  any paint type, needs a primer coat to adhere well to it, then a finish clear coat to protect it from scratches,  I wanted an easy and time saving process to rebuild that oxide layer….

After hours of watching youtube tutorial videos, about anodizing aluminum, stainless steel, parkerizing knives, Nickel plating, black patina on steel ….etc… I found exactly the tutorial I am looking for :


You can check the scientific journal publications here :



The process is quite simple & do not require anything expensive, for instance a black oxide professional  patina kit costs between 30 to  70 USD ,  for this experiment All I need is a household cheap product , Sink & Drain Cleaner  : Caustic Soda ( Sodium Hydroxide ) or NaOH  ( 350 gramms costs about 1.5 $  )




I will not go into the details & chemical reactions, I am not a Chemist  , all the info are in the website I already quoted, to say it simple, it is an Electrolytic treatment of the steel, in a highly Alkaline & hot Solution ( about 90°)  ,  applying a low Voltage ( 2 V to 2.3V )  &  using a sacrificial Steel Rod as a Cathode.

here is my setup :
-Mom’s Gaz Range
- Stainless Steel Bowl   ( important : never use Aluminum , the Alkaline solution will literally eat it )
-wood bar to hold Anode & Cathode
- 50% Caustic Soda deionized water solution -  I put half a bottle ( about 175 Grams NaOH )  in about a liter of water  & it worked fine. ( never add water to caustic soda or any other alkaline or acidic chemical,  the reaction can be dangerous, always  gradually add the chemical to the water so all the released heat is absorbed by the water.)
- Use Gas MAsk & gloves , the fumes are really nasty , & the chemicals irritating, i touched the parts with bare hands after the process, some of my fingerprints are half erased ?

- Thermometer to check Solution temp , I don’t have a suitable one so I just left the solution boiling for a brief moment then turned the gas button at lower state.
- some electric wires
- Anode (+) :  stainless steel preferably , avoid aluminum-Brass- Copper…etc
- Cathode (-) : Must be Steel,  Mild Steel, the kind that rust easily, preferably, grind it to bare steel before using it for better reaction.
- ATX spare power supply
- will use my DIY fan controller to regulate the voltage to 2.2 V  ,  it is possible to use 2 x AA batteries to get about 3 volts, however, the result may be unpleasant,   it is advisable to use a power source that can hold high Amperage & preferably short circuit protected ,  the cores of my circuits are LM350T  Voltage regulators, you can google for  schematics & build your own , there is a lot of possibilities with LM 317 , LM338 , LM350 , they work almost the same :

- All the Parts to Anodize  must be treated with degreaser before operation,   I used  a paint stripper, then a bath of Hydrochloric acid to prep the screws,  then rinsed them with deionized water, they turned fade Light Grey.

Some photos of my setup :



My First Attempt : 

I consider this as a failure, the cage i’ve made to hold the screws is made of galvanized steel grill , for some reason, the cage was getting all the blak oxide to it & not the screws,



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Second Attempt :

I used Crocodile pliers As Anode, & hold just one part to anodize, getting it as close as possible to the cathode & avoiding short circuits as I can , luckily,  power source is short circuit protected.
60 seconds  bath for each part.


Hurrraaaa !!! it worked  ?:




The result is not exactly the same for all the pieces, I was expecting this to happen, I was a bit in a hurry, I didn’t measure the solution temperature, I bet some pieces were getting a lower temp bath then some others  a critical detail I ignored …. I wasn ‘t using a stopwatch to check the immersion time either. some are getting tiny rust spots , may be a bad preparation before the whole process !! 

By the way  I tried to scratch the oxide with my nails  & it is sticking to the bare metal as hell,
I can tell this thing is way more durable than any paint.

Theoretically, it is better to use a sealing solution to protect that layer of oxide, any paint clear coat can do the job, I just left the parts at free air , going to check tomorrow if they get rusty , the sealing coat may be unnecessary, who knows !! ?

Conclusion : this is only a test to check if it is feasible.   & Yes , Anybody can DIY Black Oxide At Home. 
Cheers  ?


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This is the Third attempt with few improvements in the process , the outcome is better :

As a first step, cleaning then  preparation with Hydrochloric acid , it is an activator, the metal surface turn more porous right after that, as a result,  the black layer will stick better  :



Then a quick Rinse with deinonized or distilled water then I  put the parts in the blackening Bath :


I’ve Extended the immersion time to about 5 minutes ,  larger parts may need some more time for thicker black layer , I will redo the big screws later   :

 This is a picture of the preparation & post-treatment stages :


From Right to Left :

1- preparation : Hydrochloric acid bath
2- Cleaning mix :  water & degreaser (to use just  right before & after the immersion process )

3-  Diesel Engine mineral oil  ( this is a temporary sealant to avoid corrosion )
4- Final parts : actually hesitating , I will see later if I'll just dry them from excessive oil, or clean them & paint with clear coat

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To select the best sealing coat , I did a corrosion test , the parts were left in tap water for 24 hours ( there is a more severe test using salty water but I think we do not need this for indoor parts, we are only pc modders afterall,  :


2 screws were left with engine mineral  oil coating, 2 others were cleaned, dried then coated with WD40 , the last ones were cleaned from all chemicals, then submerged in water , here are the results :



that is clear that WD40 is the winner  ?

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A little trick :


If one day you try this experiment, and  after a few minutes from getting the parts out of the blackening bath , you find a salty deposit ( picture above) , do not worry, these are just  caustic soda  crystals, appearing on the surface after the pieces cool down, you can remove them easily using a toothbrush, then clean the parts with any alcohol based cleaner , I used glass cleaner & it worked perfectly,  then apply a sealing coat with WD40 .


:wub: Best Achievement :
Here are some pics of the best pieces today , I’m really satisfied , this is exactly the desired result :



This technique  works great for tools , I black coated my scratched  Dremel chuck , & my Drill Chuck key ,  they turned like brand new :



Still a ton of screws to do, I don’t think I am able to achieve this tomorrow, unfortunately, today my gloves were perforated & I got chemical attacks on the tip of my fingers, now everything I hold make me feel like burns on my fingertips, even my smartphone fingerprint unlock do not recognize me anymore.:unsure:



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Yeah, I missed this thread, otherwise I would have suggested salad tongs or taping a stick to your clip at least. -Also a NIOSH respirator. It takes years to find out you cooked your lungs sometimes, and it's always too late.

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10 hours ago, Cheapskate said:

Yeah, I missed this thread, otherwise I would have suggested salad tongs or taping a stick to your clip at least. -Also a NIOSH respirator. It takes years to find out you cooked your lungs sometimes, and it's always too late.

@Cheapskate thanks for the advice , I bought a pair of thick gloves yesterday, they are perfect for this task ..... 
during the first day of this experiment I was wearing a respirator, second day I wasn't ...I progressively  lost that uncomfortable feeling   , I think I developed  some tolerance to this chemical ... few years ago the same thing happened when I was working with polyester filler, it was smelling too bad, then I started to get familiar with it ?   I don't know if this a natural human body progressive adaptation or just a feeling, all I can say is that the cooked lungs thing you mentioned ... is scaring me out ?

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According to the study, For better scratch & corrosion resistance, a 450° heat treatment for 15 minutes is advisable.

I missed this important step so I had to degrease the parts & put them in the oven with max temp settings ( 20 minutes  , around 300° that is my oven maximum) :




I tried to scratch some of the items  & felt that the oxide layer just became more robust than before the heat treatment

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Best Sealant & final products :

Final Step, best sealant combination I’ve tested is to paint the screws heads with Nitrocellulose Laquer clear coat, which has a good penetration capability, it can anchor to the the Black Oxide magnetite pores underneath,  making the whole surface more resistant  to shock & friction ,
Acrylic clear coat can also be used.
 then the threads were soaked in WD40, I didn’t paint them to not alter their geometry.


Finally , the little soldiers  are ready  :wub: :




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