Sorry for my ignorance! But what is the problem/intention here? Why you have to test 20 materials instead of simply take the CuSn8 alloy like Panerai did?
Have you tried to find a cheaper material which has a similar oxidation/color behavior?
CuSn8 isnt only a combination of copper and tinn. There are much more materials used, given endless possible CuSn8 combinations. Nobody knows, which exact combination of copper, tinn, phosphor, nickel, zink, iron, plumb and undefined other materials Panerai used for the 382 cases.
Definition CuSn8:
tinn (Zinn, Sn) possible percentage from 7.5 to 8.5 %
phosphor (Phosphor, P) possible percentage from 0.01 to 0.4 %
nickel (Nickel, Ni) possible percentage from 0 to 0.2 %
zink (Zink, Zn) possible percentage from 0 to 0.2 %
iron (Eisen, Fe) possible percentage from 0 to 0.1 %
plumb (Blei, Pb) possible percentage from 0 to 0.02 %
other materials (undefined) possible percentage from 0 to 0.2 %
and finally: copper (Kupfer, Cu) filled up the rest to 100%.
So, a little drop more or less from each material will bring an other color of the bronze and their oxidation, the color of the patina.
Ok, I am not a chemist, but I hope I forgot nothing