Upon the light sensitivity of copper halides

[Raghu Kuvempunagar]

Came across this interesting discussion with many interesting examples on a Copper halide based process, critical details are missing though:

Lomography - A Wild Adventure Into Cupric-Solarizations with Quinn Balazs

We had a chat with Lomographer Quinn Balazs a.k.a. qbalazs who explained the intriguing and laborious work on cupric-solarizations. This developing and printing technique is a difficult challenge that Quinn was brave enough to take!

www.lomography.com

 

[AntonKL]

Somewhat alkaline solutions of certain compounds (which typically act as complexing agents for Cu2+, not as reducing agents) will develop cuprous halide crystals by triggering disproportionation of Cu1+ in the exposed areas, concurrently the CuCl/Br also reacts with the alkali to form yellow cuprous oxide or hydroxide. See https://patents.google.com/patent/US4427762A/en for some 80 examples.

I think this might also be the case with the pyrogallol developer he uses, and then either the pyro directly reacts to form some dye or maybe he tones the fixed out print with ferricyanide (but the color doesn't really match and prints developed this way are hard to fix/wash sufficiently without some fading)