Black oxide finishing

I tried to coat index ring with black oxide. Without using medicine, with some tea bags and vinegar.

Extracted by boiling thoroughly.

It was a liquid which is near to black rather than brown.

Because I didn't know how much time I should dip it at, I soaked it for 24 hours as a test.

12 hours later, color of the liquid was changed from black to brown.

24 hours later...it is dark gray rather than black.