A little late responding. I have been reading about Zeiss Ikon over the holidays, so the thread just caught my eye. Interesting article. I have been reading the Hove books set on Zeiss Ikon (1926-1939 [Tubbs], and 1939-1972 [Berringer/Small]), and now feel I have a much better feel for what Zeiss Ikon was, how they are related to Carl Zeiss, etc. I have a few Zeiss/Zeiss-Ikon cameras and lenses from that time period, and have been a fan for decades, so it was good to get a bit more educated. This article was very detailed specifically on the Tenax (which I do not own). Thanks for posting.