The authoritative public forum
  for Metal Finishing since 1989
-----

Blackening of iron piece washes off

Please tell me why blackening of iron washed off while washing, which is done in hot caustic solution. Please give response as soon as possible.
Thanks in advance.

Ajay aggarwal
- Panchkula, Haryana, India
2003

---

We'd like to help you, Ajay, but you do provide any detail whatsoever, making it nearly impossible.

But further, this is your fifth question, on a fifth topic, and it's getting a little silly that you want to complete every one of your postings in ten seconds while leaving us to struggle with every possible scenario for every possible question instead of you taking the time to detail your situation :-)

The Metal Finishing Guidebook says that the temperature must be reduced to 255 °F to blacken cast iron and malleable iron, but it's impossible to know whether the temperature or the composition of blackening solution, or something else is the problem when we have nothing to go on except "hot caustic solution". Please provide all the details you know: what type of part, what kind of iron, more details on blackening process, does it happen to some parts or all parts, did it formerly work correctly, what is the washing procedure which is washing off the blackening (Immersion, scrubbing, scotch brighting? Detergent, solvent, plain water?). Thanks!

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003