It’s aaaaall in the process! What we don’t see is the glass substrate lying on the chair, being exposed to UV light (Sun). Sandwiched within is the acidified and chemically coated paper with the desired negative for another Van Dyke print that he is currently dodging (as seen in the image above).
Burning and dodging are photographic printing techniques to improving and improvising on the tonal range of an image. It is done manually during the exposure time of the image to a UV light source or/and even during the dark room printing process. Burning increases exposure to areas that need to be darker whereas dodging is the technique to be followed in order to decreases light from entering areas that need to be lighter.
For this image, Tashi continued to cover the area that needs to be lighter (dodging) at intervals of 2 minutes for a total of 10 minutes. After which he let the image expose evenly for about 10 more minutes. The first trial was not completely a success because the dodged area had turned a bit foggy (this was maybe due to the quality of paper).