I started making Piezo prints in 2001 - first using Sundance inks, as I recall, then PiezoTone and now K7 . My prints still look great. Back then the entire focus was on the inks, with emphasis placed on 100% pigment composition for maximum longevity. Paper issues were not initially addressed. Then we learned that atmospheric conditions can detrimentally affect the paper, bringing about a different mode of failure. This is, I assume, why some people spray their prints. I have not experienced paper failure with the two mat papers I use, Photo Rag and Innova Smooth Cotton. Quite possibly, my thinking is stuck in 2001.
Can somebody please illuminate my understanding of the pro and con arguments associated with protective spray on mat papers? (I think we're talking about an aerosol after-treatment, not the in-line Gloss Optimizer.) If the spray is a varnish, don't we know from museum oil painting experience that varnish darkens or becomes opaque with time? What is considered the current best practice, and why?