This tool allows you to darken the tones of the colors in an image.
Click on Burn on the Tools bar.
In the "Burn Options" dialog select a size and shape for the brush (see Brushes).
Choose the tonal range on which to concentrate from the following:
Highlights concentrates on the lighter tones, making them darker, but also affects the darker tones.
Midtones concentrates on all tones, making them darker, apart from the very light or dark.
Shadows concentrates on the darker tones, making them darker, but also affects other tones.
Adjust the value in Exposure to change the amount of tonal darkening you want to allow. A higher value results in a greater darkening over the tonal range chosen.
Proceed to drag the Burn pointer over the areas you want to change.
See: