Currently I use regular clear "varnish" spray (the kind you would use for wood) and it works fine. The problem is that oxygen penetrates paper from behind too: I sprayed the front of a print and placed a piece of clear tape on the back. Many months later the ink behind the tape faded less.
About using pigment: two problems. First, Epson heads don't work with pigment ink (at least not the 1430W which are exactly the same heads I had on an R220 10 years ago). Second, photo paper doesn't work with pigment either. The water evaporates but the pigment is just dry dust on top of the photo paper. This is the reason why my HP K8600 didn't use black for photo paper. If you forced it to (selecting regular paper on the driver), you got the "powder" problem. Pigment black for the HP was something else though.
HP was always far better than Epson when printing black text. My HP 692C printed much better text than my cousin's Epson 440 in 1996. And this was still true in 2006, and still is in 2016.