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Need to blacken or discolor cast iron

September 5, 2008

I have a cast iron part I need to make black or discolor. After the part is discolored or blacken I am going to saw the part in half. The color only needs to be dark enough for a vision system to detect the difference between the black side and the cut side.
I am going to cut and grind the rest of the surface off but the finish can not dramatically effect the thickness.
Ideally I am looking for a system that does not need heat, rinse the part after wards, non toxic, and takes no longer that 1~2 minutes.
Thank you

Bob De Rose
Mfg Engineer - Muskegon, MI, USA

Cold black oxide may suffice for the stated need. However, it takes more than one rinse, takes longer than 2 minutes and is mildly toxic in most formulations.

James Watts
- Navarre, Florida
September 10, 2008

Try tannin solution(2o gm tannic acid [on eBay or Amazon]/19 mll phosphoric acid/1 lit water-simple DIY rust converter [on eBay or Amazon] ).It must be wax or clearcoated. Hope it helps and good luck!

Goran Budija
- Cerovski vrh Croatia
September 15, 2008