DIY Steel Blackening with Vinegar – Why the Uneven Finish?

[asto]

Thanks for the informative response Lee.
You know, for me, the vinegar approach was a way to escape the harse chemicals trap eventhough the NaOH + NaNO3 method gives me top results every single time.
Yes, i understand that for two main reasons these parts came with uneven oxide color.
First and foremost must have been poor cleaning as you very rightful say with second the spring steel alloy elements contained in it.
This last one i can not control.
So the parts i am trying to darken are made in a progressive die and the blanks are 0.3mm thin spring steel.
But...trying to mark some of these parts today by etching with FeCl3 which was the left over from a PC board work of the past.
I came across a pleasant surprise.
I accidentally found a new oxidizing method.
That of FeCl3. And this approach is speedy. It blackens the parts almost instanly. I mean several seconds after immersion.
I tried to upload images of these parts yesterday but i failled to locate the upload link or button in this page or elsewhere in the forun. I was looking for the "add an attatchment" icon
but it wasn't there.

Cheers!