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Re: Darkening cast iron? *LINK* *PIC*
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Darkening cast iron? ()

Gary Smyth
There is a chemiical by epi electrical products #404 https://www.epi.com/contact/

Never tried it. Only found by search on Google.

Muriatic acid gives a rust to black variation but not pure black.

The Blackening Process: Ultra-Blak 404

For the longest-lasting, deepest, and cleanest black finishes, we recommend the following blackening process. Please read all safety data sheets and technical data sheets prior to beginning a project.
1. Clean

Soils such as cutting oils, coolants, lubricants, and rust inhibitors must be removed from the metal workpiece. Soils can inhibit the blackening process and negatively affect coating adhesion and appearance. Thoroughly clean and degrease the parts prior to beginning the blackening process.
Recommended Cleaning Products:

E-Kleen SR 102-E emulsifies oils and cleans difficult-to-clean metalworking fluids and carbonaceous smut.
E-Kleen SR 102 floats oils, cleans difficult-to-clean metalworking fluids and carbonaceous smut, and results in a longer-lasting clean.
E-Kleen SR 196 is a low-caustic cleaner that floats the oil, resulting in a longer-lasting clean. It's effective up to 210º F.

2. Rinse

After cleaning the metal parts, rinse them in cold, overflowing tap water; it’s necessary to rinse the parts to remove residual cleaning solution. Parts carrying over un-rinsed film of alkaline cleaning solution would quickly contaminate the subsequent chemicals in use, resulting in a spotty or non-adherent black finish.

Immerse the parts to be blackened for 30–60 seconds.
3. Activate

Activate the metal parts in hydrochloric acid (50% by volume) for 30–60 seconds.
4. Rinse

Rinse in cold, overflowing tap water for 30–60 seconds.
5. Blacken

Immerse the parts in a boiling solution of Ultra-Blak 404 until a deep black color develops. Required immersion times may vary from 5–10 minutes, depending upon the mass, type, and surface condition of parts.
If Ultra-Blak 404 isn't quite what you’re looking for, consider these similar products:

Insta-Blak 333 is an easy-to-run, room-temperature blackening process that saves energy.
Ultra-Blak 404-L is the liquid version of Ultra-Blak 404, which makes it safer to add to a blackening tank.

6. Rinse

Rinse in cold, overflowing tap water for 30–60 seconds to remove residual blackening solution and ensure sealant will not be contaminated.
7. Seal

Seal the black-oxide finish by immersing the still-wet parts in a corrosion-inhibiting and rust-preventative solution. E-Tec corrosion inhibitors are formulated to rapidly displace the residual acidic solution from the preceding rinse and produce long-term corrosion protection. As the E-Tec is absorbed, it enhances the depth of black, which may take several hours.
Recommended Sealing Products:

E-Tec 504 is a solvent-based, water-displacing rust preventer that results in a hard, dry finish.
E-Tec 510 is an economical, water-soluble oil that offers rust protection and contains no solvents.
E-Laq 525 is a water-based lacquer that offers a hard, dry, and corrosion-resistant finish.

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