I have heard about putting pieces in hot oil but not sure how to
There are a couple of different methods of getting a nice black.
Heating with a torch until the metal goes past blue will give a deep
gray/black. It’s the finishing material that brings out the deep
black. I’ve used old motor oil, shortening, and inexpensive vegetable
oil and achieved blacks with each. As you begin to heat the steel,
start applying the oil thinly with a rag or spray it or use an
inexpensive boar bristle paint brush. It’ll smoke, so have some good
ventilation. As the oil starts to heat, it’ll get thick and change to
a deep golden color, then to brown, and finally to black. There’s a
fine point where it’s black and when it starts to burn off. It may
take you a few layers of heating and oil to build up a nice even rick
deep black. Just like with a cast iron skillet on the stove.
Another finishing method is to get the steel heated to the deep gray/
black. Let it cool, and then spray with a clear acrylic lacquer. It
comes in a gloss, satin or matte. Experiment with the thickness or
number of layers.