Amazing test to fine tune bromizing and exposure times of plates by Irving Pobboravsky .
“The three vertical panels were given 10, 13 and 16 seconds bromine. Moving the dark slide incrementally three exposures were given. Starting from the lowest horizontal band, the exposures were 1, 2 and 4 minutes at f/8. Hg-dev’d 168F, 4 minutes. I wanted the background to be solarized blue by overexposure. Light panel faced the back of the sea shell; pointed at the camera. Sea shell lit from the side by a separate light. Using the information in the test plate I chose 13 sec bromizing; 2min exposure for shell and 8 min for background exposure.”