I have some of the older Azo that I bought from an individual. (Grades 1 through 4). I print on both the older and the newer paper. The older paper has a luminescence that the new paper does not possess. (Not that the new paper is bad by any means). Michael Smith indicated that Azo had been through several reformulations in the time that he has used it. Some of the older paper had Cadium as an ingredient of the emulsion.