This technique enables you to darken a portion of your image. First
expose your print as normal. Then simply hold an opaque object over
everything but the section you wish to darken and turn on the enlarger light
for a few seconds. Quickly move the object back and forth to prevent an edge
from forming. Make test strips of both the main image and the selected
portion to determine the lengths of exposure.
Below is an example of the burning technique.
