Trace amounts of cadmium were allegedly the secret sauce to both the original Oriental Seagull G and Portriga emulsions. Once that ingredient got banned, these papers were never the same. The ban itself, and its timing, is well documented. Oriental had to comply because so much of its paper was being shipped to Europe, just like how the ban on thorium affected lens glass manufacture. Cadmium was soon highly restricted in the US as well (but ironically, not in batteries, which use far more of it). But specific emulsion formulas were well guarded secrets; and in that respect, all that many of us have to go on is the most probable rumors of the era.