Black Oxiding problems and questions

A. Hi, Alireza.

We have dozens of threads about black oxiding on the site, so you can search the site for each of your questions, and then post a follow-up on closely-related if the answers were unclear of didn't cover your situation. It would take an unfocused book-length thread here before your questions are fully answered in depth, and all I can offer here is a brief introduction ...

0. What do you mean by 'needles'; surely not hypodermic needles? Knitting or crochet needles maybe? Please give us some idea of their size, function, and production rate. Thanks.

1. I assume you are saying that when the solution is not in use, and you allow it to cool down, it hardens and crystallizes? I expect this is true, but I would not add any ingredients to try to solubilize the deposits. Rather, arrange better insulation and scheduling so that you can afford to keep the solution hot, and make sure you always wear protective gear when using it or restoring it to service.

2. I agree that black oxide can be, and usually is, done without potassium cyanide.

3. Yes, stainless steel can be black oxided but black oxide is a conversion coating, i.e., the metal itself is a part of the coating. So, actually, not only must formulation and operating conditions be slightly different for stainless steel than plain steel, those conditions will vary even from one steel to another, as gunsmiths will tell you. I don't know exactly what must be done for generic black oxiding of stainless steel as most shops use proprietary solutions for that purpose.

Regards,