Black oxidation: short & clear
Chemically blackening metal in 5 steps.
By default, you work with five steps: cleaning (degreaser) → rinsing → blacks → rinsing → sealing.
Only with difficult steel do you add an activation + extra rinsing step (then it is 7 steps).
These 5 steps are based on bare, unrusted and unpainted metal. Is there rust, old paint or mill scale? First remove blacks.
5 standard steps
1. Cleaning (degreaser)
Goal: all oil, coolant, grease and rust inhibitor gone. Residues disturb blackening (spots, poor coverage).
Use a water-based, alkaline degreaser and follow the steps in the manual.
After degreasing, drain briefly.
- A soda solution (sodium carbonate) in warm water.
- Easy to obtain: St. Marc (soda cleaner), Dasty Degreaser.
2. Rinse
Rinse very well cold – no residue from the degreaser should remain.
30–60 s in clean, running water (not under the tap). This prevents degreaser from running to the next step.
3. Blacks
Dip for 2–4 min at room temperature in Electrolyte Black Oxide or Black Oxide Ultra. For stainless steel you use: Verzinkshop Black Stainless Steel Oxide.
Guideline concentration: 10–15% in water (read the manual for the correct mixing ratio).
Move parts lightly or stir the bath gently so that the parts come into contact with fresh liquid for an even result.
4. Rinse (cold)
Again 30–60 s in clean, running water to remove residues from the black bath.
5. Sealing / preservation
Immediately after rinsing, dip in a sealer for a few minutes. The black layer is porous and sucks up the sealer. This provides more rust protection and affects the appearance of the black.
- Verzinkshop DeepSeal (oil-based): water displacement; Suitable for indoor and outdoor use.
- Verzinkshop Acrylic Sealer (water-based): very thin, without structure.
The final depth of the black can continue to develop for several hours while the sealer absorbs.
7 steps in “hard-to-blacken” steel
Some types of steel are difficult to blacken. Then add an activation after step 2, followed by an extra flush. Then you continue with blacks (step 3).
Metals that can be difficult to blacken: chrome steel (chromium-molybdenum), tool steel, bearing steel (chrome steel), spring steel (high-carbon), gray cast iron, hot-rolled steel with mill scale, laser/plasma-cut steel.
6) Activation
Makes the surface “fresh” and reactive again.
Use Verzinkshop Metal Activator at room temperature, then rinse well.
Practical alternatives:
- Phosphoric acid solution: 5–10% v/v phosphoric acid in water, dip at room temperature for 1–2 minutes, then rinse thoroughly. (Wear PPE.)
- Deruster: dip briefly, then rinse well.
- Citric acid solution: for light oxide/film, short dipping, rinse well.
For hazardous substances, always use PPE (gloves, goggles, etc.), ventilation and test on a test piece first.
7) Rinsing (cold)
After the activator, rinse thoroughly and then proceed to steps 3–5 (rinse blacks → → seal).
Practical tips
- Clean operation: keep racks/baskets clean and drain parts briefly between steps. Then spray them over the bath you just used with a plant sprayer, so that most of it runs back into your own container and you take less with you to the next step.
- Water quality: change rinse water in time.
- Movement: light movement during step 3 prevents stains.
- Recovery is easy: damage can be re-blackened and sealed locally — without visible transition (unlike paint).