Nothing to do with ozone but with my third try on the adornment of an initial O.
A pattern of branches this time, with a few leaves (that’s the end of automn after all) and no final cleaning which left all the zinc oxide on the parts eaten by the acid bath, increasing the contrast between the two parts even more than in the two firsts attempts.
In the end, I love it too and I’m not closer to the choice of the pattern to use…