What are the key steps to obtain maximum longevity (centuries) of pt/pd prints? I know what these are for silver, but have no idea of pt/pd. What are papers one can use to achieve maximum longevity? Pt, and for the most part, Pd, are impervious to chemical reaction. So, longevity depends much on the choice of paper. I've heard that Bergger Cot 320 is good. Are there warm colored papers that meet this criteria?