Refinishing a piece that has discolored during the heating operation is difficult and time consuming. Niobium does not heat color. This is a very hard finish and works well in many applications where a black metal is desirable. The piece must be formed first because heating hardens the metal. The black oxide can be polished, waxed and even engraved and anodized.
Flame coloring Here a torch becomes the artist's brush.
A free painterly approach to the work is necessary as precise effects and color control are difficult. Softly shaded washes of color and some rainbow effects can be generated with a little practice. Almost any torch will do, as the temperatures required are not high. Large soft flames will produce areas of even color. A small hot flame will generate rainbows of color radiating out from a point.